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APPENDICES
NCHRP 24-25 Page i Phase II Appendices TABLE OF CONTENTS Appendix A. Risk-Based Methodologies.....................................................................................1 HYRISK....................................................................................................................................1 HYRISK Countermeasures Economic Calculator ..................................................................6 Probabilistic Assessment/Geotechnical/Geologic Materials ................................................12 Risk-Based Cost-Benefit Assessment/Prioritizing Methods................................................13 Risk-based Design Methods ..................................................................................................14 Evaluation of Epistemic Uncertainty ...................................................................................16 References ..............................................................................................................................17 Appendix B. Specific Documents of Special Interest...............................................................19 Plan of Action for Scour Critical Bridges..............................................................................19 Scour Critical Bridges: High-Flow Monitoring and Emergency Procedures ......................23 Scour and Flood Risk at Railway Structures .......................................................................24 Scour Susceptible Bridge Screening Program......................................................................33 Price Elasticity of Demand....................................................................................................33 References ..............................................................................................................................37 Appendix C. Survey Results .....................................................................................................39 Level 1 Survey........................................................................................................................39 Level 2a Survey......................................................................................................................51 Level 2b Survey......................................................................................................................54 Meeting with MD State Highway Administration (MSHA), February 09, 2005................60 Meeting with VDOT on March 09, 2005...............................................................................62 Additional Telephone Conversations with State DOT Officials..........................................64 Specific Survey: Traffic Characteristics versus Rebuilding Time.......................................67 Scour-Related Bridge Failure Databases .............................................................................80 Other Scour-Related Information .........................................................................................91 Management-Related Information........................................................................................99 References ............................................................................................................................102 Appendix D. Annual Probability of Scour Failure and Minimum Performance Levels ......103 HYRISK Probability Adjustments ......................................................................................103 Minimum Performance Levels ............................................................................................108 Appendix E. Non-Destructive Evaluation..............................................................................112 Introduction..........................................................................................................................112 Surface NDE Methods .........................................................................................................113 Borehole NDE Methods .......................................................................................................117 Selection of NDE Methods for Unknown Bridge Foundation Depths...............................122 Effectiveness of NDE Methods............................................................................................122 NDE Conclusions .................................................................................................................125 References ............................................................................................................................125 Appendix F. Scour Management Case Studies......................................................................126 The Initial Bridge Survey....................................................................................................126 Case Study Evaluations and Responses .............................................................................131 California Bridges................................................................................................................132 Florida Bridges.....................................................................................................................169 New York Bridges ................................................................................................................205 North Carolina Bridges .......................................................................................................242 Tennessee Bridges ...............................................................................................................277 Texas Bridges.......................................................................................................................319
NCHRP 24-25 Page ii Phase II Appendices Appendix G. Scour Evaluation Forms and Tables.................................................................359 Data Collection.....................................................................................................................359 Scour Risk Probability Tables .............................................................................................363 Minimum Performance Levels ............................................................................................364 LIST OF FIGURES Figure 1 Flowchart for HYRISK methodology...........................................................................1 Figure 2 Probability of failure versus expected life...................................................................7 Figure 3 Economic benefit of protection versus countermeasure protection levels.................8 Figure 4 Minimum reasonable expenditure for countermeasure ...........................................11 Figure 5 Maximum benefit from expenditure on countermeasure.........................................11 Figure 6 Maximum benefit/cost from expenditure on countermeasure .................................12 Figure 7 Scaling and adjustment of the HYRISK annual probability of failure table ........106 Figure 8 Final annual probability of failure estimates .........................................................107 Figure 9 Minimum performance levels for each functional classification............................110 Figure 10 Annual probability of failure and minimum peformance levels ..........................111 Figure 11 Surface echo tests ...................................................................................................114 Figure 12 Bending waves method ..........................................................................................115 Figure 13 Ultraseismic testing method..................................................................................116 Figure 14 Spectral analysis of surface waves test .................................................................117 Figure 15 Parallel seismic method .........................................................................................118 Figure 16 Induction field method ...........................................................................................119 Figure 17 Borehole radar method...........................................................................................120 Figure 18 Crosshole tomography method ..............................................................................121 LIST OF TABLES Table 1 Probability of Scour Failure Using NBI Data ..............................................................4 Table 2 Scour Vulnerability versus NBI Items 60 and 61 ........................................................5 Table 3 Bridge Overtopping Frequency versus NBI Items 26 and 61......................................5 Table 4 Example Benefit/Cost Analysis of Scour Countermeasures ........................................9 Table 5 Sample Input Table for Countermeasures Costs .......................................................10 Table 6 Assumed Number of Lives Lost in Bridge Failure.....................................................21 Table 7 Categories and Priorities Based on Priority Rating...................................................26 Table 8 Elasticity of Various Measures of Travel Demand.....................................................35 Table 9 Elasticities Used To Determine Travel Demand for Bridge Detours........................37 Table 10 Level 1 Survey Respondents......................................................................................39 Table 11 Tabulation of Responses to Importance of Rebuild Time Factors ...........................69 Table 12 Tabulation of Responses to Weights of Rebuild Time Factors ................................70 Table 13 Summary of state records regarding scour failures at bridges................................81 Table 14 Minimum Performance Levels for Bridges .............................................................108 Table 15 Effectiveness of NDT Methods ................................................................................123 Table 16 Case Study Respondents..........................................................................................126 Table 17 Bridge Case Study Comparison...............................................................................239 Table 18 Overtopping Frequency ...........................................................................................363 Table 19 Scour Vulnerability ..................................................................................................363 Table 20 Annual Probability of Scour Failure .......................................................................364 Table 21 Minimum Performance Levels ................................................................................364
NCHRP 24-25 Page 1 Phase II Appendices APPENDIX A. RISK-BASED METHODOLOGIES During the review of available literature, several risk-based methodologies were encountered, some of which may be useful in development of guidelines for managing bridges with unknown foundations. The following subsections discuss a variety of methods that have been proposed or used to assess risk. HYRISK The HYRISK methodology estimates the risk of scour failure using pertinent items from the National Bridge Inventory (NBI) database, namely as the product of the probability of scour failure and the economic consequence associated with scour failure. A general flow chart for the methodology is presented in Figure 1. Figure 1 Flowchart for HYRISK methodology The original HYRISK equation is presented below. Probability of Scour Failure (P) Bayesian Posterior Failure Probability NBI Items 26, 60, 61, 71 NBI Item 27 Revise P if Outside Binomial Age Expectations P Risk ($) NBI Items 19, 26, 29, 49, 52 Exogenous Economic Parameter s Expected Consequence of Failure ($)
NCHRP 24-25 Page 2 Phase II Appendices â⬠⫠â©â¨ ⧠â¥â¦ â¤â¢â£ â¡ +ââ âââ â â++= S DAdTCTOCDAdCWLCKPRisk 100100 1 4321 where: Risk = risk of scour failure ($/year), K = risk adjustment factor based on foundation type and type of span based on NBI items and where available from more developed databases, foundation information, P = probability of failure based on NBI items 26, 60, 61, 71, and 113 C1 = unit rebuilding cost ($/ft2), W = bridge width from NBI item 52 (ft), L = bridge length from NBI item 49 (ft), C2 = cost of running vehicle ($0.25/mi), D = detour length from NBI item 19 (mi), A = average daily traffic (ADT) from NBI item 29, d = duration of detour based on ADT from NBI item 29 (days), C3 = value of time per adult in passenger car, ($7.05/h in 1991), O = average occupancy rate (1.56 adults), T = average daily truck traffic (ADTT) form NBI item 109 (% of ADT), C4 = value of time for truck ($20.56/h in 1991), and S = average detour speed (40 mi/h). The risk adjustment factor, K, permits downward risk adjustments based upon knowledge of the structural and/or foundation design. The equation is given below. 21KKK =
NCHRP 24-25 Page 3 Phase II Appendices In this equation K1 is a bridge type factor based on NBI data, and K2 is a foundation type factor based on information, which may be obtained from State inventories but not in the NBI. The values presently recommended for K1 are 1.0 for simple spans and 0.67 for rigid continuous spans with lengths in excess of 100 ft. This factor adjusts to reflect the benefit of structural continuity which can compensate for loss of intermediate supports. The factors are subjective, based on a limited delpic survey and data developed in FHWA RD-85-107, Tolerable Movement Criteria for Highway Bridges (1). The influence of actual rigidity, type of structure, etc., has significant effects on the tolerable movement criteria, which may be defined as an increase in maximum stress to a point below yield, therefore precluding the collapse case. The values recommended for K2, given below, should be developed for both abutment and pier condition, selecting the largest value for the analysis.  1.0 for unknown foundations or spread footings on erodible soil above scour depth with pier footing top visible or 1- to 2 ft below stream bed  0.8 for pile foundations when length is unknown, are less than 19 ft, or are all- wood pile foundations  0.2 for foundations on massive rock These factors are again subjective and should be revised or adjusted using local experience or further forensic studies. It should be noted that even structures supported by massive rock foundations may still incur damage due to inadequate waterway openings or other causes. Therefore, the risk adjustment factor cannot by definition be zero in a dollar- based risk analysis. The probability of scour failure is estimated using Table 1 in one of two ways, depending on the code recorded for the bridge in NBI field 113. If the NBI field 113 ranges
NCHRP 24-25 Page 4 Phase II Appendices from 0â9, then this code is used for the scour vulnerability in Table 1. However, if NBI field 113 is coded as âUâ (unknown foundation), âTâ (tidal), or even â6â (no scour evaluation), a scour vulnerability may be estimated using Table 2 using NBI items 60 (substructure condition) and 61 (channel and channel protection). Similarly, the overtopping frequency in Table 1 is obtained from Table 3 using NBI items 26 (functional class) and 71 (waterway adequacy). Table 1 was originally developed by three experts in bridge scour and occurrence, namely Jorge Pagan, Philip Thompson, and J. Sterling Jones of the Federal Highway Administrationâs Turner-Fairbank Highway Research Center in McLean, VA. The Idaho Department of Transportation reviewed this methodology and concluded that the annual probabilities of failure in this table are too large, but that the relative patterns are useful for ranking the vulnerability of bridges with unknown foundations. Table 1 Probability of Scour Failure Using NBI Data Overtopping Frequency (Use Table 3) Scour Vulnerability (Use NBI Item 113 code or Table 2) Remote Slight Occasional Frequent (0) Failed 1 1 1 1 (1) Imminent failure 1 1 1 1 (2) Critical scour 0.4567 0.4831 0.628 0.7255 (3) Serious scour 0.2483 0.2673 0.3983 0.4951 (4) Advanced scour 0.1266 0.1373 0.2277 0.2977 (5) Minor scour 0.00522 0.00648 0.0314 0.05744 (6) Minor deterioration 0.18745 0.2023 0.313 0.3964 (7) Good condition 0.18745 0.2023 0.313 0.3964 (8) Very good condition 0.00312 0.00368 0.0144 0.02784 (9) Excellent condition 0.00208 0.00216 0.0036 0.006
NCHRP 24-25 Page 5 Phase II Appendices Table 2 Scour Vulnerability versus NBI Items 60 and 61 Substructure Condition (NBI Item 60) Channel Protection (NBI Item 61) (0 ) F ai le d (1 ) I m m in en t F ai lu re (2 ) C ri tic al S co ur (3 ) S er io us S co ur (4 ) A dv an ce d Sc ou r (5 ) M in or S co ur (6 ) M in or D et er io ra tio n (7 ) G oo d C on di tio n (8 ) V er y G oo d C on di tio n (9 ) E xc el le nt C on di tio n (N ) N ot A pp lic ab le Failure (0) 0 0 0 0 0 0 0 0 0 0 0 Failure (1) 0 1 1 1 1 1 1 1 1 1 N Near Collapse (2) 0 1 2 2 2 2 2 2 2 2 N Channel Migration (3) 0 1 2 2 3 4 4 4 4 4 N Undermined Bank (4) 0 1 2 3 4 4 5 5 6 6 N Eroded Bank (5) 0 1 2 3 4 5 5 6 7 7 N Bed Movement (6) 0 1 2 3 4 5 6 6 7 7 N Minor Drift (7) 0 1 2 3 4 6 6 7 7 8 N Stable Condition (8) 0 1 2 3 4 6 7 7 8 8 N No Deficiencies (9) 0 1 2 3 4 7 7 8 8 9 N Not Over Water (N) 0 1 N N N N N N N N N Table 3 Bridge Overtopping Frequency versus NBI Items 26 and 61 Waterway Adequacy (NBI Item 71 code) Functional Class (NBI Item 26) (0) (1) (2) (3) (4) (5) (6) (7) (8) (9) (N) Principal arterials, interstates (01, 11) O O O O S S S R N Freeways, expressways (12) Other principal arterials (02, 14) Minor arterials (06, 16) Major collectors (07, 17) F O O O S S S R N Minor collectors (08) Locals (09, 19) Br id ge cl os ed U nu se d F F O O O S S R N Overtopping Frequency Annual Probability Return Period (years) Never (N) 0 never Remote (R) 0.01 >100 Slight (S) 0.02 11 to 100 Occasional (O) 0.2 3 to 10 Frequent (F) 0.5 <3 The HYRISK methodology was originally used to prioritize bridges with unknown foundations for foundation investigation through the ranking of relative risk. These risks are based on the following:
NCHRP 24-25 Page 6 Phase II Appendices  Data readily available in the National Bridge Inventory (NBI)  Basic economic assumptions  The assumption that unknown foundations are generally poor (shallow or susceptible to scour) HYRISK Countermeasures Economic Calculator The HYRISK model proves useful in answering the question it was originally concerned with: Without extensive additional and bridge-specific data gathering, which bridges represent the greatest annual expected loss due to failure or heavy damage due to scour? Risk rankings produced by the model, however, are not intended to be used to place hard actual monetary values on losses; nor were they intended to be used as direct guidance to bridge owners to answer the current question: How much is reasonable to spend on scour countermeasures to protect a bridge with a known, finite life before scheduled replacement? To begin answering this question, the probability of failure during the life expectancy of the bridge must be calculable. The lifetime probability of failure (PL) is related to the annual probability of failure (PA) in the following way: ( )LAL PP ââ= 11 . Rearranging this equation yields the expected life of the bridge (L) as follows: ( ) ( )A L P PL â â= 1log 1log . The modeler should use the first equation above if the probability of failure at a specific point in time (such as with a scheduled bridge replacement) is desired. However, the second equation should be used if the modeler wishes to determine the bridgeâs expected life given an acceptable probability of failure while the bridge remains in service. Modelers
NCHRP 24-25 Page 7 Phase II Appendices are encouraged to adjust PA based on what may be known about the specific bridge being investigated. As an example, if scour analysis indicates that a bridge will fail during a 20-year return period flood, PA should be set to 0.05. For such a bridge, the graph shown in Figure 2 gives the probability of failure in any year between the present and 100 years hence. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 10 20 30 40 50 60 70 80 90 100 Expected Life (years) P ro ba bi lit y of F ai lu re Figure 2 Probability of failure versus expected life Lacking specific data about the costs associated with bridge failure, the modeler may use the values calculated by HYRISK. However, if better numbers are available, they should be used to obtain a tailored risk value. The extension of HYRISK allows for an additional cost lacking in the original HYRISK calculations â that associated with injury or loss of life. Using these, the cost of bridge failure may be calculated as follows. LF PCR = In this equation R is the risk (value of expected loss) due to failure and CF is the cost of failure, including injury and loss of life. A reasonable measure of resources appropriate for protection of a particular bridge is the present benefit value of any countermeasure contemplated. This value may be calculated using the following equation.
NCHRP 24-25 Page 8 Phase II Appendices ââ âââ â â²â= LLF PPCB In this equation B is the present value benefit and â²LP is the probability of failure over the expected life of the protected bridge. This relationship may be used to explore the range of economic benefits offered by providing various levels of protection at the bridge site. Consider a bridge with a cost of failure of $1,000,000 and, without countermeasures, the bridge has an annual probability of failure of 0.05 and a lifetime probability of failure of 0.51 over an expected life of 14 years. For this bridge, the benefit of countermeasures calculated using the previous equation for protection up to 100 years is shown in Figure 3. $0 $50,000 $100,000 $150,000 $200,000 $250,000 $300,000 $350,000 $400,000 0 10 20 30 40 50 60 70 80 90 100 Return Period Protection of Countermeasure (years) B en ef it Figure 3 Economic benefit of protection versus countermeasure protection levels The benefits calculated above, however, ignore the costs of implementing the countermeasures. To decide on a particular countermeasure appropriate for the bridge, these costs must be included. This can be done using a simple benefit-to-cost ratio or net benefit analysis for candidate countermeasures. Consider three countermeasures which might be feasibly employed at the bridge site shown in Table 4.
NCHRP 24-25 Page 9 Phase II Appendices Table 4 Example Benefit/Cost Analysis of Scour Countermeasures Countermeasure Cost Return Period Protection (yrs) â² LP Net Benefit Benefit/Cost Ratio Small Riprap $125,000 25 0.435 -$50,327 0.60 Large Riprap $175,000 50 0.246 $88,642 1.51 Grout Mats $275,000 100 0.131 $103,746 1.38 Bridge owners may use this information to make a better-informed decision about which form of protection provides economic value while accounting for the expected (or desired) service life of the structure. The basic question can now be addressed: how much money should be spent on a bridge with a limited remaining service life to reduce the risks associated with major damage or failure. Three determinations may be made, as follows. 1. The minimum design return interval to balance costs of countermeasures with risks 2. The countermeasure design return interval that will yield the greatest net cost benefit 3. The return interval that will yield the maximum benefit/cost ratio It is envisioned that scour countermeasures would not be a consideration unless at least some elements of the bridge are scour critical. It is further envisioned that one would have access to a scour evaluation in order to determine the return interval that would cause failure or major expected damage if no countermeasures are provided. Further it is required that countermeasure costs can be assigned for protection to various levels of flooding above that return interval. A single bridge risk analysis is dependent on cost data associated with various probabilities of failure or major damage levels and it is reasonable that these costs should be provided by the designer as input to the model. Countermeasure costs are unique for each bridge.
NCHRP 24-25 Page 10 Phase II Appendices A designer may have several countermeasure alternatives available. It is also reasonable to assume that one alternative will be either preferable for some non-economic cause or be the most cost effective for a given flood level. This alternative may then be selected, and its cost used. For example, the designer may choose small riprap for lower level flooding with lower velocities, choose a larger class riprap for intermediate flood levels, and choose cable-tied block or another alternative for high flood levels because the next size riprap may be unavailable or prohibitively expensive. A sample input table for countermeasure costs is illustrated in Table 5. Table 5 Sample Input Table for Countermeasures Costs Return Interval (yrs) Design Velocity (m/s) Type of Countermeasure Cost Comment 20 2.5 none $0 Failure R.I. with no protection 25 2.75 Class I riprap $50,000 50 3.0 Class II riprap $75,000 75 3.2 Class II riprap $75,000 100 3.4 Class III riprap $100,000 200 3.7 Cable-tied blocks $175,000 The lower level of protection that should be considered can be visualized by plotting the annual risk costs and the annual cost of providing protection against return interval as illustrated in Figure 4. The lines may be quite irregular but they cross where the risks balance the costs of providing protection. If budget conditions allow for a higher level of protection the designer could either maximize the net benefit or the cost-benefit ratio. The net benefit, as illustrated in Figure 5, is the decrease in risk costs (over providing no protection) less the cost of the countermeasure. The cost-benefit ratio, as illustrated in Figure 6, is the net benefit divided by the cost of the countermeasure.
NCHRP 24-25 Page 11 Phase II Appendices Return Period Protection of Countermeasure (time) C os t ( $) Risk Cost of Countermeasure Minimum Investment Figure 4 Minimum reasonable expenditure for countermeasure Return Period Protection of Countermeasure (time) N et B en ef it ($ ) Maximum Benefit Figure 5 Maximum benefit from expenditure on countermeasure
NCHRP 24-25 Page 12 Phase II Appendices Return Period Protection of Countermeasure (time) B en ef it /C os t R at io Maximum Benefit/Cost Figure 6 Maximum benefit/cost from expenditure on countermeasure Probabilistic Assessment/Geotechnical/Geologic Materials One focus of the literature search was to identify work that has used probabilistic methods to estimate the probability distribution of a particular parameter (e.g. material property) or the likelihood of performance of geologic or geotechnical materials. The objective was to identify applications in which probabilistic methods have been used where there has been a strong reliance on qualitative information, where engineering or scientific inferences may be necessary. The nature of problems of this type necessarily involves the use of professionals to evaluate and interpret available information (i.e. make subjective assessments or elicit expert opinion). The literature search identified a number of papers in which probabilistic methods have been used to evaluate geotechnical and geologic problems. None these methods or applications were applicable to our problem, but a summary of them is presented as follows. A number of cases were identified in which subjective assessments were used to evaluate geotechnical structures. McCann et al. (2) applied a Bayesian approach to update the frequency of failure of dams based on observed conditions obtained during periodic
NCHRP 24-25 Page 13 Phase II Appendices (visual) dam safety inspections. This approach uses updated likelihood estimates based on professional interpretation of the severity of observed conditions at a dam and the degree to which these conditions are a precursor to failure. The Bayesian approach they proposed allows them to consider the relative likelihood that observed/known conditions are consistent with projects that have failed in the past, as opposed to cases in which those same conditions have been observed at projects that have performed well. Anderson et al. (3) applied a condition indexing method to develop a risk index or prioritization scheme for embankment dams. The input for the risk index is obtained from visual inspections of dams. This method is based on subjective observations: a damâs hazard potential, the relative importance of potentially deficient elements of a dam, and the severity of the elementâs deficiency. The U.S. Army Corps of Engineers has developed and applied condition index systems for a number of different structure types, including gates and concrete structures. Johnson and Niezgoda (4) applied a failure modes and effects analysis method and subjective evaluation scales (a so-called risk-based approach) to determine risk priority numbers for bridge countermeasures. This method determines a risk priority number based on subjective assessments of consequence, likelihood of occurrence, and detection. The methodology relies on rating scales developed by the authors. Risk-Based Cost-Benefit Assessment/Prioritizing Methods Methods that involve subjective evaluations of dams, as previously described, have also been used to prioritize bridges â for example Anderson et al. (3). This section summarizes some of the literature with respect to more quantitative evaluations in which risk-based cost-benefit approaches have been used to prioritize projects or actions.
NCHRP 24-25 Page 14 Phase II Appendices There are many examples of risk-based cost-benefit analyses and prioritization methods in available literature. The following is a brief summary of the work that was reviewed. Examples of application range from water resources and seismic engineering â as documented by Baecher et al. (5), Bowles (6), Kunreuther et al. (7), and McCann et al. (2) â to chemical and nuclear power industries â as documented by Postle (8). This range of application varies in a number of respects. The following gives a few examples of the different contexts in which risk-based cost-benefit assessments have been used. Â Prioritization schemes that rank or order projects in a jurisdiction (i.e., a single owner or regulatory agency) as documented by McCann et al. (2) and Bohnenblust and Vanmarke (9) Â Risk reduction benefits and project costs, as documented by Baecher et al. (5), McCann et al. (2), and Bowles (6) Â Evaluation of facilities that fail to satisfy required performance goals and must be upgraded (a preferred project remediation alternative must be selected) There appears to be a growing recognition in the literature of the importance of epistemic uncertainties (i.e. knowledge-based uncertainties) associated with conducting risk-based cost-benefit assessments. Postle (8) indicates it is important that these uncertainties be considered in the context of these evaluations. As we have discussed in our proposal, it is important to identify and carry these uncertainties through our analysis. Risk-based Design Methods A search was performed to identify applications in which risk-based criteria have been used to establish design requirements for civil systems. These examples include: Â Department of Energy (DOE; 10) design criteria for natural phenomena hazards
NCHRP 24-25 Page 15 Phase II Appendices  U.S. Nuclear Regulatory Commission (11) criteria for establishing the seismic design requirements for new commercial nuclear power plants The DOE has developed design requirements for seismic, wind and flood phenomena in which explicit performance goals and acceptable probabilities for unsatisfactory performance have been established. Simply stated, the design requirements are divided into the following parts.  Specified Performance Level â The physical capability or functional performance that should be maintained by a structure, system or component (e.g., maintain confinement of hazardous materials)  Acceptable Probability of Unsatisfactory Performance â This is the acceptable probability that a structure, system or component will fail to perform its specified performance level  Risk Reduction â Based on the design of structures, systems and components (e.g., safety factors, design margins) there is a risk reduction that is achieved, such that the probability of failure at the design basis load is low and the overall probability of unacceptable performance is less than the Hazard Design Probability of Exceedance (see below).  Hazard Design Probability of Exceedance â This is the annual probability that the design force/load will be exceeded. The hazard design probability of exceedance is established such that, when combined with the risk reduction, the acceptable probability of unsatisfactory of performance is achieved Due to the variety of facilities that DOE owns, a series of facility categories are defined. These categories are defined in terms of the hazard a facility poses in the event of failure. Categories range from warehouse and administration buildings to nuclear reactors.
NCHRP 24-25 Page 16 Phase II Appendices For each category a performance level (i.e., life safety, confinement of hazard materials, etc.), risk reduction and acceptable probability of unsatisfactory performance are defined. The U.S. Nuclear Regulatory Commission recently changed the way in which the seismic design basis for commercial nuclear power plants is determined. While the commission has not set a risk-based standard like the DOE did, it has the same basic approach. The commission stated that the current population of nuclear power plants is safe (i.e. their risk of failure in general, and with respect to seismic events in particular, is acceptable). With this starting point and the benefit of probabilistic seismic hazard assessments for existing plants, they determined the hazard probability for several seismic motions that are considered in design. With well-defined seismic design standards for structures and equipment that require adequate seismic margins, there is a significant risk reduction in nuclear power plant designs. This risk reduction coupled with the hazard design probability level results in a low probability of plant failure due to seismic events. Evaluation of Epistemic Uncertainty This part of the literature review focuses on epistemic uncertainties that are evaluated in the context of subjective assessments. There are a number of papers, books and reports that discuss the evaluation of epistemic uncertainties that must be evaluated on the basis of professional assessments (also referred to as expert elicitations or subjective evaluations). Examples include Budnitz et al. (12), Baecher and Christian (13), EPRI (14), and Vick (15). The evaluation of epistemic uncertainties involves a number of subjects. These include the selection of experts, the elicitation process (e.g. interaction with experts, how information is elicited, and feedback), epistemic uncertainty model building (identification and representation of uncertainties), and quantification.
NCHRP 24-25 Page 17 Phase II Appendices The report by Budnitz et al. (12) discusses alternative levels of expert elicitation in the seismic hazard area (i.e. geology and seismology). This report describes an approach for conducting expert elicitations when engineering and scientific interpretations/inferences are necessary to assess model parameters and different interpretations of available information. References 1. Moulton, L. K., H. V. S. GangaRao, and G. T. Halvorsen. Tolerable Movement Criteria for Highway Bridges. Report FHWA-RD-85-107. Federal Highway Administration, Washington, D. C., 1985. 2. McCann, M. W. Jr., J. B. Franzini, E. Kavazanjian, and H. C. Shah. Preliminary Safety Evaluation of Existing Dams. Report No. 69. John A. Blume Earthquake Engineering Center, Stanford University, Vol 1-2, 1985. 3. Andersen, G. R., C. W. Cox, L. E. Chouinard, and W. H. Hover. Prioritization of Ten Embankment Dams According to Physical Deficiencies. American Society of Civil Engineers, Journal of Geotechnical & Geoenvironmental Engineering, 2001, pp. 335-345. 4. Johnson, P. A. and S. L. Niezgoda. Risk-Based Method for Selecting Bridge Scour Countermeasures. American Society of Civil Engineers, Journal of Hydraulic Engineering, Vol. 130, No. 2, February 2004, pp. 121-128. 5. Baecher, G. B., E. M. Pate and R. de Neufville. Risk of Dam Failure in Benefit/Cost Analysis. Water Resources Research, Vol. 16, No. 3, 1979, pp. 449-456. 6. Bowles, D. S. Advances in the Practice and Use of Portfolio Risk Assessment. In Proceedings of the Australian Committee on Large Dams Annual Meeting, Cairns, Queensland, Australia, 2000.
NCHRP 24-25 Page 18 Phase II Appendices 7. Kunreuther, K., C. Cyr, P. Grossi, and W. Tao. Using Cost-Benefit Analysis to Evaluate Mitigation for Lifeline Systems. University of Pennsylvania, Pittsburg PA, 2004. 8. Postle M. Cost-Benefit Analysis and Chemical Risk Management. ICME, Ottawa Canada, 1997. 9. Bohnenblust, H., and E. H. Vanmarcke. Research Report R82-12: Decision Analysis for Prioritizing Dams for Remedial Measures: A Case Study. Department of Civil Engineering, Massachusetts Institute of Technology, Cambridge MA, 1982. 10. DOE Standard 1020: Natural Phenomena Hazards Design and Evaluation Criteria for Department of Energy Facilities. U.S. Department of Energy, Washington, D.C., 2002. 11. Regulatory Guide 1.165: Identification and Characterization of Seismic Sources and Determination of Safe Shutdown Earthquake Ground Motion. U.S. Nuclear Regulatory Commission, Washington, D.C., 1997. 12. Budnitz, R. J., G. Apostolakis, D. M. Boore, L.S. Cluff, K. J. Coppersmith, C. A. Cornell, P. A. Morris. Recommendations for probabilistic seismic hazard analysis: Guidance on uncertainty and use of experts. NUREG/CR 6372 Vol. 1, UCRL ID 122160. Senior Seismic Hazard Analysis Committee, U.S. Department of Energy, Washington, D.C., 1997. 13. Baecher, G. B., and J. T. Christian. Reliability and Statistics in Geotechnical Engineering, John Wiley & Sons, Ltd, 2003. 14. Report NP-4726: Seismic Hazard Methodology for the Central and Eastern United States. EPRI , Palo Alto CA, 1986. 15. Vick, S. G. Degrees of Belief: Subjective Probability and Engineering Judgment. American Society of Civil Engineers, Reston VA, 2002.
NCHRP 24-25 Page 19 Phase II Appendices APPENDIX B. SPECIFIC DOCUMENTS OF SPECIAL INTEREST The literature review for this report also yielded several documents of particular interest to the current research. The following summarizes the pertinent information from each document. Plan of Action for Scour Critical Bridges In this Idaho DOT report (1) scour critical bridges are subdivided into four categories based on lifetime risk and annual probability of failure. The risk and probability of failure are calculated using HYRISK. Each category corresponds to a recommended minimum response level as described below.  Category A (Vital Scour Critical Bridges) Lifetime risk of failure for these bridges exceeds $5,000,000. This lifetime risk cutoff value was set in consultation with the ITD Scour Committee. Plan of action for Category A includes: ⢠A full Plan of Action including both monitoring and countermeasures should be developed and implemented in a timely manner. ⢠Before scour countermeasures are installed, each Category A bridge should be treated as a Category B, C, or D bridge, depending on the annual probability of failure and the structural features of the bridge. ⢠An extensive bridge closure plan has to be developed.  Category B (Extreme Scour Critical Bridges) The lifetime risk is less than $5,000,000, but the calculated annual probability of failure equals or exceeds 10 percent. Plan of action for Category B includes: ⢠Bridges should be closed under high-flow conditions.
NCHRP 24-25 Page 20 Phase II Appendices ⢠A closure plan should be developed and implemented detailing closure trigger events, closure methods, a recommended detour route, and contact information for the District Engineer and traffic enforcement personnel. ⢠Once a bridge is closed due to high flow, it should be inspected for stability prior to reopening the bridge to traffic. ⢠Hydraulic and structural countermeasures should be incorporated in the case of frequent bridge closures.  Category C (Severe Scour Critical Bridges) The lifetime risk is less than $5,000,000. The annual probability of failure is between 1 and 10 percent, or less than 1 percent, but the bridge is founded on spread footings. Plan of action for Category C includes: ⢠Develop bridge monitoring (detailed in the report) and closure plan ⢠Structural, monitoring, and hydraulic countermeasures may be developed for each bridge as funding allows. ⢠Category C bridges should be treated as Category B bridges until a monitoring plan has been developed and implemented.  Category D (Moderate Scour Critical Bridges) The annual probability of failure is less than 1 percent and driven pile foundation. Plan of action for Category D includes: ⢠Develop bridge monitoring and closure plan. ⢠Bridges should be closed if distress is observed under high flow conditions. The assumed cost per fatality is $500,000. This value assignment is obviously subjective and could vary more considerably based on both economic and sociological factors. The number of lives lost is assumed to vary depending on the ADT and functional
NCHRP 24-25 Page 21 Phase II Appendices classification (see Table 6). High-ADT crossings, interstates and principal arterials are assumed to have more potential fatalities. Table 6 Assumed Number of Lives Lost in Bridge Failure Number of Lives Lost Average Daily Traffic (ADT) 0 ADT < 100 1 100 < ADT < 500 2 500 < ADT < 1000 2 1000 < ADT < 5000 5 ADT > 5000 (Not an interstate or arterial) 10 ADT > 5000 (interstate or arterial) Unknown foundation bridges should be prioritized for further action based on lifetime risk. The bridge owner should make every attempt to determine the foundation type and depth. Once the foundation has been determined, a scour evaluation should be performed to determine whether the bridge is scour critical. Until the foundation is determined and scour depths are known, a monitoring plan with closure protocols should be implemented. Routine biennial inspections and post-flood inspections should include stream cross sections along the bridge faces and local scour depth measurements at the ends of the piers, and at the four corners of each abutment (two wingwall ends plus the two inside corners). These measurements will be taken using portable monitoring instruments such as probes, portable sonar, etc. Monitoring during high flows is a critical activity for bridges that could be destroyed or substantially damaged by a single flood. The crew performing high-flow monitoring should be focused on looking for indicators that the bridge is at imminent risk of failure. All scour-critical bridges should be evaluated for signs of bridge distress. Such signs would include the following.  Overtopping of the bridge deck or approach roadway  Pressure flow at the bridge (the low chord mostly or fully submerged)
NCHRP 24-25 Page 22 Phase II Appendices  Vertical or lateral displacement of the superstructure  Visible damage to the bridge deck, low chord, or substructure  Sinkholes in the roadway behind the abutments  Massive debris buildup, especially if near the low chord If any of these or other qualitative signs of structural distress are apparent at any time, the crew should implement an emergency bridge closure, call for formal or full bridge closure, and should avoid getting on the bridge if at all possible.
NCHRP 24-25 Page 23 Phase II Appendices Scour Critical Bridges: High-Flow Monitoring and Emergency Procedures In this Idaho DOT report (2) the following information was considered noteworthy.  Maximum expected pier scour depth ranges from 2.4 to 3 times the pier width for circular or round-nosed piers aligned with the flow  Square-nose piers will have a about 20 percent larger maximum scour depth than a sharp-nose pier, or 10 percent larger than a cylindrical or round-nose pier  Abutment scour will be most severe where the roadway embankment leading up to an abutment obstructs a significant amount of the over-bank flow  Abutment scour is greater if the abutment (embankment) is skewed in an upstream direction (into the flow)
NCHRP 24-25 Page 24 Phase II Appendices Scour and Flood Risk at Railway Structures In this report JBA Consulting (3) conducted a study that examined an existing priority system for evaluating scour potential at railway bridges. The system has been in use in the UK for some time and was reviewed for its effectiveness at assigning high priorities to bridges. The results in the report appear to show that the priority system is effective. After reviewing the system and railway bridge data the study recommended the threshold for assigning a high priority be changed, and showed that a calibrated threshold level would give more bridges a high priority. The report also addresses a number of topics that go beyond foundation scour at railway bridges. For instance, based on a review of historic incidents, they noted there are several significant modes of failure that contribute to the overall risk of bridge failure, thus putting into context the relative fraction of the time foundation scour occurs. They also discuss issues regarding flood design for railway bridges and acceptable risk. There appears to be no direct link between their priority rating system and acceptable risk. The study looks at priority ratings and flood frequency, which is related but not the same. For example, it is not clear whether a structure that is assigned a high priority (and thus, would require some form of immediate attention) was assessed to determine the prevailing risk or whether it is acceptable or not. This would appear to be an important step with respect to maintaining a balanced safety approach and efficient allocation of resources. The main focus of the research was on scour failure of railway structures that cross a water course. An old prioritization scheme was modified by factoring in more bridge data. The current British system uses a conservative âPriority Scoreâ to prioritize risk associated with scour. Action will be taken once the score crosses a certain threshold value. The key issues considered include the following.
NCHRP 24-25 Page 25 Phase II Appendices  What is a failure?  How should failure(s) be categorized?  What indicators can be used to readily identify structures prone to scour damage/failure?  What are the uncertainties in scour and flood risk identification?  What is an acceptable ratio of estimated scour depth to estimated foundation depth? Toward this end, the study did the following:  Created a database of all points where an existing rail network crossed a water course (8,438 structures including bridges and culverts)  Evaluated âPriority Ratingâ (PR), which indicates the degree of risk associated with bridges failure due to scour  Found that complete data is available for 2,924 out of 8,438 structures  Verified the accuracy of the data using GIS This research concentrates on 2,924 structures for which complete information is available. Among 2,924 structures a total of 9,305 bridge supports or elements (an element is an abutment or a pier) have been rated. Classification of 9,305 elements is as follows: The change of bed depth (total scour) at a bridge structure is assumed to be composed of three components. The first component is Regime or Natural scour (due to 9,305 Structures 1,336 â Known Foundation (FD) 7,969 â Unknown Foundation (NonFD) 7,120 Foundation Depth = 1 m (assumed) 849 Foundation Depth of zero or greater (assumed)
NCHRP 24-25 Page 26 Phase II Appendices river) (TR); the second component is contraction scour, scour due to watercourse dimensions by the structure; and the third component is local scour, caused by flow discontinuities at the structure. The summation of contraction scour and local scour is termed total scour (TS). Preliminary Priority (PP) = 15 + ln (TS/FD) PP for most bridges is between 10 and 20. Final Priority Rating (PR) = 15 + ln (TS/FD) + TR + FM FM = Foundation material Table 7 gives categories and priorities based on the final priority rating calculated. Table 7 Categories and Priorities Based on Priority Rating Priority Rating Category Priority >17 1 High 16 - <17 2 High 15 - <16 3 Medium 14 - <15 4 Medium 13 - <14 5 Low <13 6 Low The distribution of foundation depths measured for 1,336 elements were studied both on linear scale and on logarithmic scales. It is estimated that the mean value for foundation depth is 1.2 m and upper and lower SD values are 2.4 and 0.4 respectively. Hence the default value of 1 m foundation depth is very close to known foundation statistics. If the foundation depth is not available (from drawings) then usually foundation depth is estimated using coring. This establishes the depth of pile cap or strip/pad foundation and will therefore provide a conservative estimate if the structure is founded on piles or is protected by timber coffer dam. If the foundation depth is unknown then FM=0 Hence PR = 15+ln (TS/FD) + TR (TR ranges from -1 to 0)
NCHRP 24-25 Page 27 Phase II Appendices And PP= 15+ln (TS/FD) For fixed TS and FD =1m study established high priorities for 50.5% of elements using preliminary priorities and high priorities for 26.6% of elements using final priorities. Some of the event(s) causing the failure:  Highly localized flashfloods  Severe storms of moderate spatial extent The study established a relation between the average return period* of flood and Priority Rating. For example, a rating of 16.5 will fail for a 10-year flood; where as a rating of 14.4 will fail for a 1,000-year flood. The study also considered structural failure of bridges with unknown foundation but did not establish an overall priority number. The author, Jeremy Benn of JBA Consulting was contacted in order to gather additional information. The paragraphs summarize the questions put to him and his responses. Question: We are concentrating our research on highway bridges in United States. Do you think your methodology is applicable to this situation (as your methodology primarily concentrates on railway bridges)? For example, the methodology calculates a priority number and this number might be appropriate for US highway bridges where foundation information is available. In the absence of such data, your assumption of a foundation depth of 1 meter may not be appropriate for our study. In other words, the general methodology might be appropriate, but assumptions used to fill in missing data might not be appropriate. Do you have an opinion on this? Response: There is no fundamental technical reason why the method cannot be used for highways. The UK Department of Transport indeed looked at the method over 10 years ago with a view to adopting it, but for some reason decided to develop its own (an unpublished procedure known as Advice Note D - which has never actually been adopted).
NCHRP 24-25 Page 28 Phase II Appendices The causes of undermining scour are the same whatever the use of the bridge, namely flood conditions, an erodible material and the presence of bridge supports in a river. The use of the bridge really only has an influence on the consequences of failure and the mitigation options available (for instance it is slightly easier on a railway to close the bridge to traffic if need be). The assumption of a minimum of 1m foundation depth if no information is available is very much the buck stop. While it may sound arbitrary, the depth was close to the mean of the available coring records (which it should be noted would not have included any pile depth). If there is evidence that piles exist, this minimum depth could be safely increased. In our research we did ask the question, are there some additional factors unique to railways that may make them more vulnerable to scour? In the UK most of our railway bridges are over 140 years old and were built before methods of steel/deep piling were available. A common construction method was to use timber piles with a timber pile cap on top. However road bridges of the same age were also built this way - so this is an age rather than use issue. However, railways do have two features that do not always occur with road bridges - they cross rivers and floodplains on embankment (and hence there is less potential for overtopping, which increases backwater and hence flow depths during flood) and they are more often skewed relative to the river due to the limited curves allowable on rail track. It is interesting that in the two floods on the Eye Water (1846 and 1948), when all the railway structures collapsed, the 17th century masonry arch road bridge over the same river survived. The only reason we can surmise for this (other than luck!) is that the road approaches were not on embankment and so flood 'relief' was available to the structure by means of flow by-passing the bridge by overtopping the approach road. In direct answer to your question, I think the method has potential for use in the US - particularly for bridges with piers and where the risk is undermining scour. The current
NCHRP 24-25 Page 29 Phase II Appendices work we are undertaking for the RSSB is looking at additional 'tweaks' to the method to allow it to represent abutment scour, scour at inverts and also failure due to water pressure/ loading. Question: Does "Foundation depth" in the document refers to the depth of the piles driven below the river bed if the foundation sits on piles? Response: Correct - foundation depth included the depth of pile if known. If the existence of piles cannot be confirmed then the foundation depth was taken as the proven depth (usually the bottom of the pile cap/raft which can be established by core drilling through the bridge support). Question: What does the term "Foundation Material" mean? Is this the material on which the foundation sits or the material used to build the foundation? Response: Foundation material is the material on which the foundation lies. As this is often unknown, it is considered to use as a substitute the material in the river bed adjacent to the support which can be established by site investigation. Question: Your research concentrates on 2,924 structures for which complete information is available. Are these structures strictly limited to railway bridges or did you consider any highway bridges? Response: They were all railway bridges. The reason for this is the work was commissioned by the railway industry. Also in the UK it is the railway industry which has been at the forefront of research and pro-active management of scour risk following a bridge collapse in 1987 and so records and data are much more readily available. My impression is that in the US the opposite is true - most of the work has been on highways. On other work we have undertaken, we do have much more limited data for road bridges, and there appears to be good correlation between the foundation depths and scour risk if you compare bridges of a similar age and construction.
NCHRP 24-25 Page 30 Phase II Appendices Question: Among 2,924 structures a total of 9,305 bridge supports or elements (an element is an abutment or a pier) have been rated. When you established the priority (Preliminary Priority (PP) or Final Priority Rating (PR)), my understanding is that you established priority for an individual element. If a bridge has multiple piers then how do you come up with one priority score for the structure? Response: We simply took the highest score of any support. We looked at other options such as weighting the scour or taking an average, but we found the additional effort/complexity did not really add any value. The reasons why we assess the supports individually are (a) it is then clear where the main risk to the structure lies and (b) it reduces the over conservatism of assessing the structure as a whole where you may well assess the risk based on the maximum scour depth and minimum foundation depth even if they were not at the same support. Question: In section 2.4 "Summary of the Analysis" you have indicated that probability of uncertainty associated with a range of ( +,- ) 1 is 67%. How did you obtain this? Response: Hopefully the attached Word document explains how the figures were derived. Question: Once the bridge engineer establishes a priority (Low, Medium or High), are there any recommendations regarding a course of action based on the priority? Response: Yes there are lists of standard recommendations for each category. In summary these are: Â Low - reassess at a suitable interval (normally 6 years but may be longer or shorter depending on circumstances) Â Medium - monitor and reassess at a suitable interval (normally 3 years but may be longer or shorter depending on circumstances)
NCHRP 24-25 Page 31 Phase II Appendices  High - study in more detail to quantify the risk more accurately and to assess mitigation options that may be required (e.g. scour protection, flood warning). In the meantime however, interim measures are required immediately to monitor the structure during flood and to receive flood warnings. Question: From the chart I can see if foundation depth = 0.01 m and Total scour depth = 10 m then a bridge element has a medium priority where as if foundation depth = 0.01 m and Total scour depth = 50 m then it has a high priority. From a scour stand point does it really matter whether total scour depth is 10 m or 50 m for a foundation depth of 0.01 m. Does it structurally matter whether foundation depth is 10m or 50m (as far as failure is concerned)? On a broader sense if the scour depth is more than foundation depth, I think there can be only one probability of failure. Please let me know what you think about this. Response: From a structural viewpoint it doesn't really matter what the scour depth is once it is below the foundation depth as the result/consequence is probably the same. For local scour at piers, there could be an argument that the deeper the scour depth, the larger the spatial extent of the scour hole and hence it does present a greater threat to the stability of the structure. However the main reason for allowing the priority score to increase as scour depth increases beyond foundation depth is that the uncertainty in the scour depth estimate being greater than a critical threshold (i.e. is it in practice going to be deeper than the foundation) reduces with scour depth. The Railway Scour Assessment Procedure (referred to as EX2502 in the UK), calculates a Priority Score based on the ratio of estimated scour depth to foundation depth. The scour can then be further modified for other factors such as risk of blockage and the presence of scour counter measures. If a 1:1 ratio of scour depth to proven foundation
NCHRP 24-25 Page 32 Phase II Appendices depth is used as a critical threshold the majority of structures on the railway network would be assessed as high priority â a result that is clearly overly conservative and out of sorts with the known historical incidence of scour and flood failure. For this reason, EX2502 sets the critical threshold at 16.0. This requires the estimated scour depth to be at least 2.7 times the proven foundation depth. This appears at first a less than conservative threshold, but in practice is not. It is actually a result of the inherent conservatism of the available equations for estimating scour depth, and also the difficulty in establishing foundation depth and condition for structures. It is also probably a reflection that other risk factors (other than undermining due to scour) are being lumped in to the priority score.
NCHRP 24-25 Page 33 Phase II Appendices Scour Susceptible Bridge Screening Program In this report Renna (4) of the Florida DOT describes a general overview of the bridges crossing various cannels in district four. Based on experience and bridge inspection reports it is concluded that most of the bridges crossing manmade channels are not susceptible to scour. This report also describes quantitative scour evaluation program but does not address the issue of âhow to maintain bridges with unknown foundationâ specifically. Price Elasticity of Demand Price elasticity was investigated as a possible cost of failure, but was not included the final cost equation. This reviews the pertinent findings of this research. Travel demand models were originally developed in the late 60âs and early 70âs to analyze the need for new or modified highway facilities. First models were used to generate information about demand in six broad categories:  Number of trips  Destination of trips  Route selection  Travel time  Mode of transportation  Volume of current traffic within the network Over time models have become more sophisticated and look at freight demand separately from passenger vehicle demand. Price is the direct, internal, variable, perceived cost involved in consuming a good. Price is not limited to monetary costs but can include non-monetary costs such as time, inconvenience and risk. Price changes often impact consumption decisions and can drive trade off decisions or demand shifts.
NCHRP 24-25 Page 34 Phase II Appendices Average daily trip demand is impacted when transportation costs increase. Small price changes can create demand shift if there are competitive options. Many businesses make site selection decisions based on proximity to raw materials and end users and tend to optimize site location depending on transportation, labor and tax implications. Distribution functions are also significantly influenced by monetary transportation costs and service time to market variables. Elasticity is defined as the percentage change in consumption of a good caused by a one-percent change in its price or other characteristics such as travel time, or road capacity. If prices decline, generally travel increases as lower-value trips become more affordable, conversely if price increases traveler may choose to forego trips, chain trips together or shift to different mode, route or destination. Travel demand is often considered inelastic. Even with increases in fuel prices and taxes, motorists have historically not given up their vehicles. Some columnists contend that compared to Europe and Asia our price of fuel has not reached a high enough level to cause a shift in consumer travel demand. Fuel prices maybe considered to be a poor indicator of elasticity because of the new choices now available for hybrid vehicles and improved fuel efficiency in new vehicles. Fuel is considered to be only about one quarter of the total cost of driving, or a -0.3 elasticity of vehicle travel with respect to fuel price. Fuel is estimated at about 15% of total vehicle expense for the traveling public. Fuel is the second highest expense for a truck driver or about 28% of their total operating cost.
NCHRP 24-25 Page 35 Phase II Appendices Table 8 Elasticity of Various Measures of Travel Demand Dependent Variable Short Term Long Term Total Fuel Consumption Mean elasticity -0.25 -0.64 Range -0.01 to -0.57 0 to -1.81 Fuel Consumption Per Vehicle Mean elasticity -0.08 -1.1 Range -0.08 to -0.08 -1.1 to -1.1 Total Vehicle Kilometers Mean elasticity -0.10 -0.29 Range -0.17 to -0.05 -0.63 to -0.10 Vehicle Kilometers Per Vehicle Mean elasticity -0.10 -0.30 Range -0.14 to -0.06 -0.55 to -0.11 Freight transportation companies have mechanisms in place today to recognize the variable cost of fuel. Fuel surcharges are often included in rate contracts and can be indexed to national or regional fuel price indices. Mileage or route choice is often a factor included in rate contracts. The Household Goods Carriers Guide is a widely accepted resource for determining trip mileage. Many factors impact price sensitivity and can influence travel behavior. Some of these variables include: ⢠Vehicle purchase price ⢠Registration fees ⢠Fuel price ⢠Emission standards ⢠Tolls ⢠Parking fees ⢠Transit time ⢠Trip purpose ⢠Freight value
NCHRP 24-25 Page 36 Phase II Appendices ⢠Day of week ⢠Income level In general high value freight and business/commuter travel is less elastic than recreational or shopping trips. Weekday travel demand is less elastic than weekend travel. Commuter peak travel windows show less elasticity than off peak travel demand. A number of port facilities and freight carriers have experimented with off peak delivery windows only to find a reduced number of facilities with the ability to load and unload freight during evening and late night hours. Price elasticity increases if good quality alternatives exist. A good quality alternative is often viewed with respect to time and effort required to make the switch. If transit time is increased substantially or if information about route, schedule or fare information is not easily accessible, mode preference is often unchanged. The price elasticity for freight transportation is complex and is mostly influenced by the value of the commodity. Full truckload volumes may be converted to intermodal (rail) freight containers, if a freight terminal is in route and access to the railroad is readily available. Less than truckload shipments are often time sensitive and the commodities are more valuable. Low value commodities often move via the lowest total cost mode and are the least sensitive to price changes. In the last five years several research projects have been undertaken to estimate and model user costs in highway work zones. Generally traffic flow rate, vehicle speed and work zone length are the significant variables. Components of these variables include: ⢠Deceleration delay cost ⢠Reduced speed delay cost ⢠Acceleration delay cost ⢠Vehicle queue delay cost
NCHRP 24-25 Page 37 Phase II Appendices ⢠Excess cost of speed change cycles ⢠Excess running costs of vehicles at reduced speed through work zones ⢠Total hourly excess user cost In general it was found that operating costs in reduced speed work zones are less but do not offset the reduced speed delay costs. The time delay variable is more important than the cost of operations. Rising fuel costs, while significant have little impact on ADT. As a percentage of total operating cost, fuel amounts to less than 20%. Time, while controversial in how it is valued, is the single largest cost of delay. Time cost varies between rural and urban area, and varies by state and region of the country. In comparison to Europe and Asia, our travel costs are far less than our global neighborâs. Changes in fuel prices, vehicle costs and personal income to date have had little impact on travel demand or growth in ADT. Considering operating costs and national travel time estimates the following elasticities may be reasonable to determine travel demand with respect to bridge detours. Table 9 shows elasticities which may be used to determine travel demand for bridge detours. Table 9 Elasticities Used To Determine Travel Demand for Bridge Detours Travel Demand Elasticity Short Term Long Term Passenger vehicle -0.16 -0.33 Truck -0.39 -0.80 References 1. Idaho Transportation Department. Plans of action for scour critical bridges. Ayers Associates project no. 32-0629.00, Boise, ID, June 2004. 2. Idaho Transportation Department. Scour critical bridges: high-flow monitoring and emergency procedures. Ayers Associates project no. 32-0629.00, Boise, ID, July 2004.
NCHRP 24-25 Page 38 Phase II Appendices 3. JBA Consulting. Scour and Flood Risk at Railway Structures. Final Report prepared for Railway Safety & Standards Board, Project No. T112, Skipton, North Yorkshire, U.K., 2004. 4. Renna, R. Scour Susceptible Bridge Screening Program. Florida Department of Transportation, District 4, Fort Lauderdale FL, 1993.
NCHRP 24-25 Page 39 Phase II Appendices APPENDIX C. SURVEY RESULTS During the literature search, a survey was prepared and distributed to State DOTs using an AASHTO e-mail distribution list. The following sections summarize the survey and individual responses. Level 1 Survey Table 10 lists the names and organizations of respondents. Table 10 Level 1 Survey Respondents Name Organization Phil Brand Arkansas Highway and Transportation Department David Kilpatrick Connecticut Department of Transportation Thomas Scruggs Georgia Department of Transportation Brian Summers Georgia Department of Transportation Paul V. Liles, Jr. Georgia Department of Transportation Paul Santo Hawaii Department of Transportation Tri Buu Idaho Department of Transportation Ben Garde Illinois Department of Transportation Gary Peterson Minnesota Department of Transportation Marc Grunert Nevada Department of Transportation Harry Capers New Jersey Department of Transportation Scott Christie Pennsylvania Department of Transportation Wayne Seger Tennessee Department of Transportation Todd Jensen Utah Department of Transportation Frederick J. Townsend, Jr. Virginia Department of Transportation James E. Sothen West Virginia Department of Transportation Finn Hubbard Wisconsin Department of Transportation The following is a facsimile of the questionnaire and a summary of the responses received.
NCHRP 24-25 Page 40 Phase II Appendices Bridge Management 1. Would you consider implementing risk-based guidelines for managing bridges with unknown foundations? 12 Yes 2 No 2. Do you believe there is a need to develop a plan of action for bridges with unknown foundations that could be implemented during and after flood events (e.g., temporarily bridge closure)? 13 Yes 1 No 3. Does your agency take a particular approach or use a particular methodology in its bridge management program to assess bridges with unknown foundations? If yes, provide a short description here. Provide copies of any documents more fully describing your approach or tell us how we may obtain them. 6 Yes 8 No Frederick J. Townsend, Jr., VDOT A scour risk assessment was performed on national bridge inspection standards (NBIS) structures with unknown foundations and on those deemed to be at risk. Consulting engineering firms were tasked with evaluating the risk and recommending actions required on a bridge site-specific basis. Ben Garde, ILDOT We keep a database and construction plans as well as microfilmed files which generally avoids the problem of having unknown foundations. Those, which do not have documentation on the foundations used, are given an increase in priority for replacement. Gary Peterson, MnDOT Our Bridge Management System tracks pier and abutment foundation types including unknown foundations. See http://www.dot.state.mn.us/bridge/ for copies of our bridge inventory reports. Look under the Structural Data section. David Kilpatrick, ConnDOT We have included bridges with unknown foundations in our group of bridges that we would monitor during a critical river flow event. Wayne Seger, TDOT For West TN Timber pile bent bridges, we have assumed a pile length of 25â when looking at scour calculations. This was a common size timber pile used in those days of timber pile bent construction in that part of the State. James E. Sothen, WV DOT Bridges with ADT greater than 1000 having unknown foundations have been core drilled. Those with non-conclusive results remain unknown. Low ADT routes with no know scour problems may be assigned low risk, often with increased inspection. 4. Do you use the results of an assessment of bridges with unknown foundations to prioritize them for foundation investigations, maintenance or repairs and modifications? If yes, briefly describe your approach here. Provide copies of any documents more fully describing your approach or tell us how we may obtain them. 7 Yes 7 No
NCHRP 24-25 Page 41 Phase II Appendices Frederick J. Townsend, Jr., VDOT Virginia is divided into nine maintenance/construction districts. The recommendations from the scour study were given over to the districts for their action. The districts put together a plan of action for each bridge to address these recommendations. These actions ranged from monitoring, to installing countermeasures, to replacement. Ben Garde, ILDOT All structures at stream crossings are analyzed to see if scour can impact the foundation and if no foundation type information is known, they are given an even higher increase in priority for replacement. Same holds true for structures in seismic areas. Harry Capers, NJDOT For âunknown foundationâ bridges that were assessed as potentially scour critical during our Screening & Prioritization program, in-depth scour evaluations were performed. During that process, we attempted to obtain foundation data by using probing, NDT or borings. In some cases, the information obtained allowed us to draw conclusions about the foundation that removed the bridge from the âunknown foundationâ category. In other cases, some inferences could be drawn about the foundation that allowed us to make judgments about the bridge during the evaluation. In other cases, no information could be obtained and the scour critical judgment was made in a very conservative manner resulting in many being identified as scour critical. Once a bridge is identified as scour critical, it is treated the same regardless of whether or not the bridge has unknown foundations. New Jerseyâs policy is to retrofit scour critical bridges with countermeasures and to monitor them during and after significant storm events until the countermeasures are installed. Gary Peterson, MnDOT If bridges with unknown foundations have experienced a scour event or have a history of scour which threatened to undermine a footing, work to protect or replace the foundation or bridge would be considered as projects are identified and prioritized. Without a history of problems, its unlikely foundation type would influence repair or replacement decisions. Bridges with unknown foundations are required to be screened. Screening may involve foundation investigations, or may be subjective based on engineering judgment derived from observation of stream flow or performance during past high water events. Until a screening is performed, a plan to monitor the foundation during flood events is required to be filed. The process is documented in our NBIS Quality Assurance Review of Bridge Owners. See http://www.dot.state.mn.us/bridge/DocumentsFormsLinks/ Paul V. Liles, Jr., GDOT If we suspect the bridge is scour susceptible, we will have the site drilled to tell us the probable location (depth) of the piles. In one case, we then used pulse-echo to determine if the piles were founded where we believed. When pulse-echo verified the depth, we replaced the bridge bents that were scour susceptible. Wayne Seger, TDOT If unknown foundation bridges are located in WTN, we look more closely at stream characteristics and histories, if known, and type of bridge design, simple or continuous spans.
NCHRP 24-25 Page 42 Phase II Appendices James E. Sothen, WV DOT Bridges are prioritized at our district level and repaired based on priority and availability of funds. 5. Does your agency use any risk-based guidelines for making transportation decisions? If yes, briefly describe them here. Provide copies of any document more fully describing your approach or tell us how we may obtain them. 5 Yes 9 No Frederick J. Townsend, Jr., VDOT The VDOT utilizes a business decision-making methodology whereby decisions are evaluated based on impact and risk. Gary Peterson, MnDOT MnDOTâs bridge scour program considers risk when assigning bridge scour ratings. An initial screening process was done to determine which bridges are âlow riskâ for failure due to scour. A secondary screening process considers risk and allows ratings such as K â limited risk to public, monitor in lieu of evaluation and close if necessary. (see Bridge Scour Evaluation Procedure for MN Bridges at http://www.dot.state.mn.us/bridge/DocumentsFormsLinks/) Paul V. Liles, Jr., GDOT Flood recurrence intervals, earthquake return periods and wind design loads are based on recurrence intervals which are risk based decisions. Wayne Seger, TDOT Question is too broad. All decisions regarding transportation issues are risk-based Tri Buu, Idaho DOT Develop Plans of Action for scour critical bridges based on quantitative prioritization using risk analysis. Contact Lotwick Reese, 208 334 8491 for more info. 6. Does your agency consider âoff-budgetâ costs (i.e., those paid for with road usersâ funds like lost productivity and the added cost of using a detour) as well as âoff-budgetâ costs (i.e., those paid for with public funds like repairs or replacement) when making bridge maintenance decisions? If yes, briefly describe here how are they calculated and balanced? Provide any documents that more fully describe your approach or tell us how we may obtain them. 5 Yes 9 No Frederick J. Townsend, Jr., VDOT I canât say that I completely understand the question but yes, VDOT does take user costs into account when choosing a maintenance methodology. A higher dollar, but innovative approach may well have less impact on the traveling public, thus making the net cost of the project less. User costs are calculated using traffic counts times hours delay times average cost per hour times project duration. Scott Christie, PENNDOT Lane rental
NCHRP 24-25 Page 43 Phase II Appendices Ben Garde, ILDOT Decisions regarding user costs are routinely made for most projects. Traffic volumes and detour lengths play an important role in those decisions. Stage construction vs. closure are routine decisions for maintenance projects. No, we do not calculate these costs directly but use their relative influence in those decisions. Gary Peterson, MnDOT ADT is considered when determining how to handle traffic during construction (i.e. to close, detour, construct half at a time, bypass, etc). No calculation of user costs is usually made but ADT has a strong correlation to user costs. Paul V. Liles, Jr., GDOT High ADT routes will be rated higher. David Kilpatrick, ConnDOT Additional Info â For bridge maintenance decisions, it is the Departmentâs policy to perform whatever repairs are necessary to ensure the structure is safe for the traveling public. The Department will routinely schedule repair activities to be performed on off â peak hours for the limited access highways to reduce the impact on the traveling public. No calculations involving roadway user or detour costs are computed in deciding the best alternative to handle traffic. Wayne Seger, TDOT We look at repair costs and replacement costs when making bridge maintenance decisions. 90% of repair work by contract is stage construction. We will recommend accelerated construction schedules to reduce âoff-budgetâ costs. 7. Does your agency use any discrete factors to determine how quickly it will replace or repair failing bridges (e.g., ADT, route classification, etc.)? If yes, please elaborate here. Provide any documents that more fully describe your approach or tell us how we may obtain them. 8 Yes 6 No Frederick J. Townsend, Jr., VDOT See Question 6. Criticality of the structure certainly plays a role in prioritizing both preventative and restorative maintenance. Brian Summers, GDOT We primarily use route classification and ADT as well as safety and extreme inconvenience issues. High volume ADT Interstate bridges are generally given priority for repair. Interstate or State Route bridges that are closed are given the highest priority for immediate repair. Ben Garde, ILDOT No, we do not have one âtop to bottomâ priority ranking system. With limited budgets, we utilize a system that categorizes structures based on their condition (deck, super, sub, etc.), ADT, load carrying capacity, as well as functional deficiencies. Roadway conditions often influence priorities too. We try to avoid load posting situations where possible. Structures within categories then compete for limited funding.
NCHRP 24-25 Page 44 Phase II Appendices Harry Capers, NJDOT Scour critical bridges that show signs of scour along their foundations are repaired as a priority regardless of their having an âunknown foundationâ or not. Should a bridge show signs of a foundation failure, the repairs are made on an emergency basis. Failed bridges are likewise either repaired or replaced on an emergency basis. Gary Peterson, MnDOT Factors are weighed informally in the program planning process. Bridge Condition, Maintenance costs, ADT, age, functional adequacy, and road system among other items all weigh into decisions of when to repair or replace bridges. Our Bridge Preservation, Improvement and Replacement Guidelines (http://www.dot.state.mn.us/bridge/DocumentsFormsLinks/) formally but somewhat loosely document our repair and replacement decision process. Phil Brand, AHTD Sufficiency ratings are considered, but are not the sole prioritizing factor for replacing state-owned bridges. David Kilpatrick, ConnDOT When prioritizing, high ADT bridges are often given higher importance. FHWA has also indicated their concurrence of this. Wayne Seger, TDOT The only factors that would accelerate a repair/replacement of a failing/failed bridge is detour. In some cases, there is no detour. Political intervention will also come into play here. Traffic demands, i.e., ADT, will also factor into the timeliness. Typical Bridge Foundation Design 1. Typically, what information does your agency have (or can easily obtain) on bridge foundation conditions (e.g., geology, geotechnical data, etc. Frederick J. Townsend, Jr., VDOT Most structures on the Primary and Interstate systems have soil boring information archived as part of the as-built plans. Bridges on the Secondary system would also have this information if the date of construction is within the last thirty or so years. Boring information is easily obtained as VDOT has in-house as well as on-call contractor drill crews. Marc Grunert, NDOT Older structures may have âTest Pitâ information, while newer structures may have âBoring Logsâ. This information may or may not be readily accessible. Brian Summers, GDOT Georgia maintains both an electronic data base of foundation information and old bridge foundation report files that contain foundation recommendations, pile driving data and occasionally as-built foundation data. Information from around 1970 to the present is fairly good and available, but information prior to this is not as reliable and sometimes not
NCHRP 24-25 Page 45 Phase II Appendices available. Ben Garde, ILDOT Our state retains the soil/rock exploration boring logs and existing structure foundation construction plans for future analysis. Most of our structures are founded on driven piling and we retain the âas builtâ pile driving records to further confirm the foundation in place. Paul Santo, Hawaii DOT Geological maps. Possible borings from a project in the vicinity. Harry Capers, NJDOT Boring logs and as-built plans are generally available. Foundation reports may or may not be available depending on the year the structure was built. Gary Peterson, MnDOT We have a foundation study typically including borings. Boring information is included in the bridge plan sheets. We also have pile driving reports and bridge construction documentation for most bridges. Paul V. Liles, Jr., GDOT Original plans, Bridge Foundation Report, As-built data, scour history â Some, All, or none of the above will be available for a given bridge. David Kilpatrick, ConnDOT Soil boring data, which is typically included in the design contact plans. If it's an unknown foundation, we won't have this data. We may have surficial and bedrock geology mapping for the area. Wayne Seger, TDOT Only on newer bridges that TDOT has design plans can one obtain geotech data. Some old design plans show foundation data at which rock was encountered. In those cases, rock may be cobble, solid, fractured, etc.; not necessarily always solid and didnât tell what type. James E. Sothen, WV DOT Many bridges have existing plans. Bridges without plans may be core drilled. Tri Buu, Idaho DOT Subsurface conditions, including soil or rock types, their engineering properties, ground water condition. Foundation type, shallow foundation size and depth, pile driving data (not always available). 2. Does your State characterize unknown foundations in any systematic way, even if it is subjective? If so, please provide a short description here. Provide any documents describing that system or tell us how we may obtain them. 1 Yes 13 No Gary Peterson, MnDOT Bridges with unknown foundations are required to be screened. Screening may involve
NCHRP 24-25 Page 46 Phase II Appendices foundation investigations, or may be subjective based on engineering judgment derived from observation of stream flow or performance during past high water events. Until a screening is performed, a plan to monitor the foundation during flood events is required to be filed. The process is documented in our NBIS Quality Assurance Review of Bridge Owners. See http://www.dot.state.mn.us/bridge/DocumentsFormsLinks/ Wayne Seger, TDOT In Tennessee, geology in the Western third of the State is typically sand and silt with no rock. In the middle third, the ground has more rock both cobble and solid limestone. There is some chert and sandstone along the perimeters of the Middle section of the State. The Eastern third is mountainous with a mix of solid rock and large angular cobble. In general Middle and East TN are the most âstream stableâ areas of the State. 3. Describe any relationship you believe may exist between a bridgeâs size parameters (e.g., span length, width, number of lanes, total length, etc.) and foundation design. Frederick J. Townsend, Jr., VDOT Dead and live loads increase with the expansion of bridge deck area, ergo loads to the foundations increase making them larger or more complex. Brian Summers, GDOT Bridges with relatively short spans (<50 feet) and relatively short unsupported pier lengths (<20 feet) generally will have pile bents (top of pile directly supports the cap). Bridges with longer spans and long unsupported pier lengths will generally have pile footings (piles support a footing on which a column is poured that supports the cap), spread footings or drilled shafts. Some large bridge widenings that had scour-critical pile foundations that maintained the existing superstructure during construction used drilled shafts. Ben Garde, ILDOT We do not have any established relationship. Obviously, as the structure becomes larger and the loads become higher, it is more likely that the foundation is on piling. However, as the foundation soils become stronger and more difficult to drive piles (rock), it becomes more likely that the foundation is a spread footing. Harry Capers, NJDOT There is no direct relationship between the size of the bridge and foundation. The size and type of foundation depends on the subsurface conditions. Gary Peterson, MnDOT No historically reliable relationships. Typically larger spanned bridges carry heavier loads and require stronger foundations which would include pile footings. Bridges over rivers and navigable waters typically will have stronger foundations to resist ice loads and ship impacts which would include pile footings. Paul V. Liles, Jr., GDOT The bigger the bridge, the bigger the foundation.
NCHRP 24-25 Page 47 Phase II Appendices Phil Brand, AHTD Of bridges with unknown foundations: In parts of the state without rock or rock-like soil at or near the surface, short span bridges(< â40â) have driven piles; longer spans are often supported by wall-type piers with foundations below channel bottoms. In parts of the state where rock is near the surface, spread footings are common. Wayne Seger, TDOT We have never really looked at this type of relationship. On bridges we have design plans for, the foundation details only show the footing size and if piles were designed for footing support (material of piles are identified) but not pile length. James E. Sothen, WV DOT Bridges on major routes typically have foundations on rock. Foundations may be spread footings, piles or caissons. 4. Describe any relationship you believe may exist between a bridgeâs age and its foundation design. (Distinct foundations designs may dominate among bridges built in distinct time periods?) Frederick J. Townsend, Jr., VDOT Many of our older structures were built on timber piling. Also these older structures were built on spread foundations with less concern regarding scour. Brian Summers, GDOT Some older bridges (built in the 40âs and 50âs) used timber pile foundations, but there is generally not good correlation between the time periods and foundations used. Foundations were designed based on bridge layout and site-specific conditions. Ben Garde, ILDOT The older the bridge, the less likely it is supported by drilled shafts. The older the bridge, the more likely it is supported by timber piles (unless rock is close or the load demanded end bearing h-piles. Paul Santo , Hawaii DOT For older bridges, there doesnât seem to be a relationship. These days almost all bridges over streams are on piles or drilled shafts. Gary Peterson, MnDOT No historically reliable relationships. Older bridges (pre 1950), if they have pile foundations, often used untreated timber piling with little restriction on source. Paul V. Liles, Jr., GDOT Designs change over time â use of timber piles, bigger spread footings, use of caissons â these can often be dated to the bridge era in which a structure was built. Phil Brand, AHTD Older bridges (>25 years) tend to be supported by timber piling and more massive wall-type
NCHRP 24-25 Page 48 Phase II Appendices piers. Wayne Seger, TDOT Many older bridges (prior to 1960s) used timber piles to support concrete footings and substr. Also West TN used timber pile bents as the substructure elements for bridges. Concrete piles came along in 60âs and are still used today. Steel piles have always been used, especially in Middle & East TN. Until recent years, when steel piles are used, one would assume they are point bearing on rock. In recent years, steel piles and steel pipe piles are being used due to the fact that the length can be extended by welding another section. James E. Sothen, WV DOT Major bridges that are old generally found on rock using timber or steel piling, concrete spread footings. All bridges built since late 50âs and early 60âs have foundations supported on rock. Very few if any erodible foundations built since 1960. Tri Buu, Idaho DOT Deep foundations of very old bridges are typically timber piles with vertical design loads in the range of 10 to 20 ton/pile. 5. What site-specific parameters may be used to infer foundation design? Frederick J. Townsend, Jr., VDOT Site-specific soil boring information will give the foundation designer a depth to, and the bearing capacity of competent rock or firm material. This information will also characterize the soil types as to whether, and to what depth, scour is likely. This information will determine if a deep (bearing or fiction piles) or a shallow spread foundation is most appropriate. Marc Grunert, NDOT None exists to my knowledge. Two, virtually-identical structures may exist in close proximity. Yet one will be built on spread-footings and the other on piling. Brian Summers, GDOT Depth to rock or hard soil strata, presence of voids or limerock layers, depth to theoretical scour line, expected ease or difficulty of certain pile type installation, type work (widening vs. new construction), bridge layout. Ben Garde, ILDOT Looking at existing boring data or obtaining new boring data can give some suggestions on what type of foundation should have or could have been used. If the footing size in known or if by probing we can determine the size, it can indicate what must have been used (since the footing is too small to be a spread footing) or conversely, if the footing is very large, it can be assumed that it is likely a spread footing. Paul Santo, Hawaii DOT In Hawaii, piers and abutments within streams are likely to have pile foundations (either timber or concrete).
NCHRP 24-25 Page 49 Phase II Appendices Harry Capers, NJDOT H-Piles or steel pipe piles are used in North Jersey where soft soils sit above bedrock and concrete or pre-stressed concrete piles are used along the coastline, which is in a marine environment. Gary Peterson, MnDOT Exposed bottom of footing or piling. Settlement may indicate a spread footing is in place. Often for bridges with pile footings, the approaches will continue to settle over time in relation to the pile supported bridge. Borings that show weak soils probably have pile foundations. Borings showing shallow rock with granular overburden are likely on spread footings. It may not be necessary to know the foundation type if the bridge very low ADT or has a long history of successfully weathering scour events. Paul V. Liles, Jr., GDOT Geologic formation in which the bridge was built David Kilpatrick, ConnDOT Areas of known deep compressible/soft soils will likely be on deep foundations. Wayne Seger, TDOT If timber piling was used, a common length timber was 25â-30â, especially if it is a pile bent. Shorter timber piles were common used if the substructure was a timber pile supported concrete footing. Typically, if there are steel H-piles involved in either a pile bent or pile supported footing, we have assumed it point bearing on rock. James E. Sothen, WV DOT Dept to competent rock and quality of rock. Depth of scour. 7. What factors do you recognize to cause bridge foundation structures to deteriorate over time (e.g., materials, salt water, etc.)? Provide (or tell us how we may obtain) any data, documentation, or reference to quantify the relationship between such factors and deterioration over time. Frederick J. Townsend, Jr., VDOT Piles used as bents will deteriorate over time especially in the tidal zone of salt or brackish water. Ground water pollutants can also damage foundation piling. Marine borers will damage unprotected timber piling. Scour can diminish the effectiveness of spread foundations and if severe enough can diminish the effectiveness of a pile foundation. Marc Grunert, NDOT While adverse environmental factors, as well as materials used, may impact foundation deterioration, we have no data, documentation, or reference to quantify to relationship(s).
NCHRP 24-25 Page 50 Phase II Appendices Brian Summers, GDOT Corrosion of exposed steel piles in certain environments. However, exposed steel is protected with concrete encasing and bituminous or paint coatings, thus reducing or eliminating this problem. Some timber piles used as bridge fender systems in coastal environments degrade and are replaced as needed. We do not keep any data to quantify any deterioration. Scott Christie, PENNDOT Scour â and salt contamination Ben Garde, ILDOT Years of wet and dry cycles have been damaging to our timber piles. In soils with high chlorides and sulfides, we have seen aggressive corrosion of sheet, h-piles, and metal shells. Have no documentation to provide. Paul Santo , Hawaii DOT Salt water on steel and reinforced concrete foundation structures mainly at the tidal and splash zones. Rocks and debris hitting foundation structures within relatively fast moving streams. Sulfate attack on concrete foundations (although I have no knowledge of an occurrence at any of our bridges in Hawaii). Harry Capers, NJDOT Foundations typically deteriorate in the splash zone but there is no data substantiating the rate at which this occurs. Gary Peterson, MnDOT Downstream of a Paper plant an anaerobic bacteria that eats steel piling is present in the water. The rate of deterioration is a concern and consideration is being given to encasing the piling. Timber piling tend to deteriorate more rapidly at the air/earth or air/water interface. They may be solid above and below this area. Paul V. Liles, Jr., GDOT Exposure to the elements, salt water, scour, corrosion, freeze-thaw are all factors that cause bridge deterioration. Phil Brand, AHTD Rust of exposed steel piling, rot and insect attack of wooden piling. Occasionally, stream bed-load has eroded concrete surfaces of piling and columns, but has not generally gotten to the foundation itself. David Kilpatrick, ConnDOT Factors that cause bridge foundations to deteriorate may include scour, material quality, poor construction techniques, salt, ASR, and poor or incorrect designs. No documentation exists quantifying the relationship of these factors and the rate of deterioration overtime experience in the state.
NCHRP 24-25 Page 51 Phase II Appendices Wayne Seger, TDOT Debris build up on bridge piers will damage pile bents and/or increase scour potential. Timber piling weathers quickly, especially if in a wet/dry zone. Steel piling rusts quickly in the wet/dry zones. James E. Sothen, WV DOT Deicing chemicals. We have timber piling on the river that has been in use for 80 to 100 years and are performing very well. Very few problems associated with foundations due to deterioration. Level 2a Survey Following the Level 1 survey, some respondents were contacted with follow-up questions by telephone. The following is a summary of the correspondence.
NCHRP 24-25 Page 52 Phase II Appendices Harry Capers, NJ DOT How do you determine whether the bridges with unknown foundation are scour critical or not? Do you adopt any particular methodology? Bridges on spread footings can usually be reliably estimated by probing or coring to determine the depth of the footing which essentially eliminates the bridge from the âunknown foundationâ category. Bridges on pilings are assessed using engineering judgment based on conservative assumptions of pile lengths and calculated scour depths. The following is from our scope of work for scour evaluations of bridges on pilings of unknown length: For bridges known to be founded on piles, the length of pile exposed due to scour should be determined as part of the first phase. If the length of exposure is five feet or less, the bridge will be classified as stable and SI&A Item 113 will be given a rating of â4â or â5". An exception to this would be a case where pile lengths can be estimated and are known to be twenty feet or less. In this case, the consultant should evaluate whether the bridge requires additional evaluation or should be classified as scour critical and SI&A Item 113 given a rating of â3". If the exposed length is greater than twenty feet, the bridge should be classified as scour critical and SI&A Item 113 should be given a rating of â3". For bridges with an exposed pile length of between five and twenty feet, the consultant should evaluate the extent and cost of the additional analysis or non- destructive testing that will be required to determine the scour critical classification of the bridge. For these bridges, the estimated cost of scour countermeasures should also be determined for any potentially scour critical substructure element. The consultant should compare the two estimates and make a recommendation on a course of action which should be included in the scour evaluation report. If the Department decides to undertake the additional study, it will be performed as extra work in a second phase of the analysis.
NCHRP 24-25 Page 53 Phase II Appendices What kind of counter measures do you adopt for scour critical bridges with unknown foundation? Do you prioritize them in any particular manner? Scour countermeasures for bridges with âunknown foundationsâ are typically designed the same as bridges with âknown foundationsâ once they are determined to be scour critical. We would typically use gabions or rip-rap. Once the bridge is determined to be scour critical, it would be prioritized based on the same parameters as any other bridge (Functional Classification, ADT, collapse vulnerability, bridge height, etc.). What kind of counter measures do you take for scour critical bridges with unknown foundations? Please provide us with any documentation. The repair of scour holes completed as a Priority Repair is not intended to provide a permanent scour countermeasure, it is intended only to repair the existing damage and usually consists of rip-rap or cement filled bags. Scour countermeasure installations are much more extensive and require environmental permits prior to construction. Frederick J. Townsend, Jr. P.E., VDOT Can you provide us with any documentation on the methodology and the recommendations provided by the consulting firms in "scour risk assessment"? The study was performed in accordance with the National Bridge Scour Evaluation Program â available on-line. How do the districts prioritize bridges with unknown foundations? Can you provide any documentation for this? The districts, through the appropriate District Bridge Engineer, have full autonomy in selecting candidates for inclusion in their maintenance/reconstruction program. Nine districts equal nine different ways of evaluating the regional bridge asset inventory. This is the long way around telling you that there is no cast-in-stone decision matrix for the prioritization process. Can you provide us with any documentation on the "business - decision making" methodology? Do a search for âbusiness decision makingâ and âVDOTâ. You should find an article in the July/August issue of the VDOT Bulletin in which there is a description of the BDM process. What kind of a duration and delay costs do you use in obtaining "user costs"? This is project specific. Given the ADT of affected roadways in the project area, we
NCHRP 24-25 Page 54 Phase II Appendices estimate what the delays will likely be in person-hours. Regionally we estimate what the average cost per person-hour is and thatâs how the user cost is developed. Is there any particular methodology you adapt to replace or repair failing bridges? Please provide us with any documentation you have. Rule of thumb has the break point between rehabilitation and replacement at 60% of replacement value. Of course this percentage is not hard and fast and final resolution lies with the district. Many issues are involved in the decision making process (see BDM). Level 2b Survey Some respondents to the Level 1 survey were contacted with follow-up questions by e-mail. The following is a summary of the correspondence.
NCHRP 24-25 Page 55 Phase II Appendices Does your organization have any database containing information on bridge foundation depth and information on soil characteristics on which foundation sits (or piles are driven)? If not a database, do you have a central location where you store as- built design drawings that would include this information? Scott Christie PennDOT We do have as builts â usually kept at District offices Paul Santo, HawaiiDOT We do not have a database. We have a central location where we store as-built drawings. These drawings usually contain foundation and soil information. Tri Buu, IdahoDOT Information on bridge foundation types, subsurface conditions, etc. are in the bridge plans kept at the ITDâs Bridge Design section. The information is also available on microfilms. We are currently creating a digital file for information of the existing bridges. William M Kramer, ILDOT No we do not have a data base. Yes we do have a central location where contract plans and as driven pile information is retained. Andrea C. H. Hendrickson, MnDOT No we do not have a database with bridge foundation depth and soil information. We do have average pile information in our hydraulics files in the Bridge Office, and plan sheets (not as-built) filed in the Bridge Office often include soil boring results. We also have the historical bridge construction file (separate file for each bridge located in a separate storage facility) for most of our bridges built since the 1930's that contain pile driving records and pile lengths for specific bridges. Brian Summers, GDOT We have a database system known as the Bridge Information Management System (BIMS) that maintains historical documents of all of our structures when the documents are available. It is an electronic historical archive and includes construction plans, foundation investigations and some as-built drawings. The records are stored in .tif files so they are not easy to query, but
NCHRP 24-25 Page 56 Phase II Appendices they are available. Wayne J. Seger, TNDOT We do not have a database that contains foundation information or soils types for each bridge in the state. On bridges that only "as built" drawings exist; we do not know what is below ground level. On some design bridge plans, we may have some information regarding soils information, foundation type and size, and in limited cases pile lengths. On bridge plans designed in the last 5 to 10 years, actual pile lengths driven are listed on the sheets. If there are design plans, they are typically kept at headquarters Structures Division and a half size is kept in the inspection report. Jack Mansfield, NJDOT NJDOT dose not have a database containing the bridge foundation system and associated geological characteristics upon which foundations sit. However, there is a document control office that stores all the as-built plans constructed by NJDOT. Also,a Bridge Evaluation Report is maintained and updated by the Structural Evaluation Unit. The Geotechnical Engineering Unit maintains the Geotechnical Foundation Report, as-drilled boring plans, and boring logs. 2. Do you have design standards for minimum foundation depth? For example, minimum foundation depth can be a minimum depth a pile should be driven or a minimum depth a spread footing be placed under the soil in your area. Scott Christie PennDOT To generalize â we use both shallow and deep foundations. Spread footings are generally a minimum of 6 ft in the ground. Pile foundations are always over 10 ft. Friction piles are normally 30 to 60 ft. And point bearing piles vary over a large range. Paul Santo, HawaiiDOT We do not have minimum foundation standards. Top of spread footings for bridges are usually placed between 2 to 4 feet below finish grade. Other structures may have soil cover of 12 inches.
NCHRP 24-25 Page 57 Phase II Appendices Tri Buu, IdahoDOT For piling foundation, our standard specifications require a minimum pile penetration of 10 feet (this specification has been revised recently requiring 20 feet minimum penetration for piles embedded in soft or loose soils). In the past, we normally placed the spread footings a minimum of 3 feet below the streambed. William M Kramer, ILDOT Yes, piles must be 10â long and spread footing must have at least 4â of embedment. Andrea C. H. Hendrickson, MnDOT Typically we try not to use piling when the length of the piling in the ground will be less than 10 feet. Brian Summers, GDOT No. Each structure is handled individually by the geotechnical engineer responsible. Minimum tip elevations for piles are determined by soil strata and scour evaluation. Wayne J. Seger, TNDOT I'm not sure if you would call this a standard, but we do not drive less than a 10 foot pile. In the last twenty to thirty years, we do not place a spread footing on soil. All footings are either on solid rock or pile supported. I have found some older bridge design drawings that show the footing to be founded on rock. However the rock shown on plans turns out to be round cobble rock which can be undermined due to scour or streambed migration. Bottom line is to be somewhat skeptical when using old design plans. Jack Mansfield, NJDOT No. Guidelines for the foundation depth are established based on AASHTO and HEC 18, Evaluating Scour At Bridges. The depth of the deep foundation system is determined by the design requirements.
NCHRP 24-25 Page 58 Phase II Appendices 3. When foundation information is unavailable are there any foundation generalizations you can make? For example, piles driven into sandy soil are typically at least x feet deep, piles driven into clay soils are typically at least y feet deep, foundations over rock are typically spread footings on the rock surface. This doesn't have to be statistically developed, we would just like your opinion based on your experience/knowledge. Scott Christie PennDOT We rarely use drilled shafts. Paul Santo, HawaiiDOT None for piles. However, we do have "default" soil design parameters provided to us from our Testing Lab. If the soil type is unknown, we assume the worst case. Tri Buu, IdahoDOT In areas where we generally know the types and conditions of subsurface materials, we may be able to guess the foundation type of an existing structure when there is no information available for that structure. For example, if the structure was built in the 1950's or earlier and the subsurface materials are loose or soft soils, we would assume that the structure were supported by timber piles with penetrations no less than 10 feet. If we know bedrock exists at a shallow depth, then we would assume that the structure was supported by spread footings placed on bedrock. Until recently, most of the bridges in Idaho were supported either by shallow footings or pile foundations. Drilled shaft foundations have been used more often in the last five years or so. There are mainly only two types of piles used in Idaho. Timber piles in the past and steel piles, either H beams or pipe piles, in the last few decades. One bridge with micro-piles is currently under construction. We don't use pre-stressed concrete piling in Idaho. William M Kramer, ILDOT No we can not say pile in clay are âxâ or pile in sand are âyâ. However, if boring data is available, the subsurface conditions and structure loadings can in some cases rule out spread footing (or suggest a spread footing if piles cant be driven) or verify that piles must have been used and they must be at least âxâ ft. if they are to carry the loadings in that soil profile.
NCHRP 24-25 Page 59 Phase II Appendices Andrea C. H. Hendrickson, MnDOT No. Brian Summers, GDOT We do not make any generalizations at this point. We are considering different methods for making some assumptions since we have a large percentage of bridges with unknown foundation elevations. We have had many different practices over the past 50 years concerning foundations so it is difficult to make an assumption for all bridges that is safe. Wayne J. Seger, TNDOT If no foundation information is known but we see steel piles called out on plans or steel piles used in a pile bent, we assume those piles are driven to rock (solid), point bearing. In west Tennessee, there is a lot of timber pile bents. These are typically driven into sandy type soils. Whenever an old pile is extracted from the ground or undermined, measurements are taken to try to assess the "typical" pile length used in that area. We have found that 30 feet is a common length for timber in that part of the state. We also have old state standards for pre-stressed concrete piling. The 14" square piles are typically no longer than about 35 feet long. The 16" square piles can stretch as long as 60 feet. Jack Mansfield, NJDOT Soil borings taken at the site are generally used to estimate the existing foundation system. Regarding pile length, the typical timber pile design capacity of 24 tons for a nominal 12-in diameter pile and a maximum length of 40 to 50 feet is used to estimate existing foundation conditions.
NCHRP 24-25 Page 60 Phase II Appendices Meeting with MD State Highway Administration (MSHA), February 09, 2005 Attendees: Andy Kosicki, Ralph Manna (Structures, Bridges) Dan Sajedi (Materials, Geotechnical) Jeff Robert Len Podell Glenn Vaughan (Chief Design Division) Rod Thornton (small structures) Currently there are around fifteen structures under the jurisdiction of MSHA with unknown foundations. Efforts have been taken to reduce the number from 50 to 15 in recent years. A majority of these structures were built prior to 1940. Once bridges with unknown foundation were identified, MSHA categorizes them into one of the following. (3a) No evidence of scour (3b) Scour susceptible (3c) Scour critical The decision making process for bridges identified as scour susceptible or scour critical (3b and 3c) depends on the age of the structure. If a bridge needs to be replaced within next 5 to 10 years, they may not adopt any measure involving significant amount of money. If a bridge has more than 20 years of life (from their experience), they adopt certain measures to counter the scour problem. The following procedure describes various steps MSHA adopts in their scour inspection program. Scour monitoring: One of the main measures they adopt is regular scour monitoring, approximately once in every two years. The field crew establishes scour depth using sounding data and compares with past records. The crew
NCHRP 24-25 Page 61 Phase II Appendices estimates change in scour depth between present and past records. If there is one foot increase in scour depth in five years, they take borings. If MSHA knows that a pier is on a spread footing, usually a 4 inch diameter hole is drilled through the footing to get soil and foundation depth information. For each pier it costs approximately $1000/boring (2 holes). The typical thickness of a spread footing is around 4 feet to 6 feet. Cost of scour monitoring depends on the size of the channel. Installing 60 grout bags per day costs approximately $10,000 to $25,000. For a small bridge (2 lanes) it costs about $10,000 to install grout bags. Streams in Maryland tend to be small but for Woodrow Wilson Bridge on Potomac River, expected cost of monitoring is around $250,000 in 1.5 years. Â Counter measures: If a crew observes more increase in scour depth (two to three feet) or if the bottom of the footing is exposed, MSHA adopts counter measures along with rigorous monitoring. Counter measures usually include placing sized grout bags or riprap. Class three grout bag has dimensions of 3â long, 4â wide and 1â deep. Grout bags usually extend to 6 feet; beyond that MSHA has permitting issues. Â Scour analysis: After adopting counter measures MSHA regularly monitors bridges. If they find more scour depth or if grout bags fail, they suspect greater vulnerability in the stream. Bridges of that nature are identified as scour critical and advanced techniques like scour analysis are used. Performing a scour analysis tends to be expensive (approximately $50,000 for survey and H&H analysis), hence they normally do not adopt this procedure unless there is a real need (e.g., large bridge with high ADT). During the course of an event MSHA monitors bridges more closely. If flow overtops a bridge with unknown foundations, they close the bridge and wait for inspection.
NCHRP 24-25 Page 62 Phase II Appendices Meeting with VDOT on March 09, 2005 Attendee: The attendee at the meeting was Frederick J. Townsend (Structure and Bridge). Virginia is divided into nine districts and each has a bridge engineer to maintain bridges under his jurisdiction. Each district is further classified into residency and each residency into headquarters. Richmond district has six residencies and each residency has up to ten area headquarters. A consultant was hired to study all bridges in the early 1990s for scour vulnerability. VDOT found that among 2,500 bridges approximately 25 bridges are scour critical and neither construction drawings nor foundation information is available for those bridges. VDOT has many other bridges with unknown foundation but those bridges are not classified as scour vulnerable. VDOT considers that if design plans for the bridges are available then the foundation is known. VDOT inspects their bridges once every two years as a part of routine bridge maintenance program. If they find no visible problem they keep monitoring the bridges. Field crew establishes scour depth using sounding data and compares with past records. Crew estimates change in scour depth between present and past records. If there is one to two foot increase in scour depth they increase monitoring and provide counter measures. Ninety percent of the counter measures are provided because of erosion due to the meandering of the stream. If they find problem in piers then they protect piers using grout bags. In order to determine the size of the riprap (as a counter measure) they may perform an approximate H&H analysis. They use USGS quadrangle map, FIS, USGS regression equations, etc to determine discharge, elevation and other hydrological parameters in determining the scour criticality of the bridge. Detailed H&H is performed only for new structures, which are scour critical. They adopt a âClass 1 Bridge Surveyâ method to perform detailed H&H. Permitting is a big concern when installing counter measures in water. After installing counter measures they monitor the performance of the
NCHRP 24-25 Page 63 Phase II Appendices countermeasures for one significant storm. If the counter measures performance is satisfactory, they monitor the bridge on a regular cycle. Most of the bridges with unknown foundations are located on rural roads in Virginia. From an economic prospective, sometimes they may build a new structure instead of repairing the old one. Bridges having timber piling may have critical scour problems if they are exposed to both dry and wet conditions. Usually timber piles are more than 10 feet deep. Spread footings are not usually found on erodable soils unless it is an older structure. Spread footings are usually two feet under the top of the soil and three feet in thickness. VDOT is unlikely to have soil information if the foundation information is unavailable. In that case they may do borings to get soil information, which gives them more confidence on their assumption regarding foundation information. Obtaining boring information is not very expensive. To get boring information by drilling approximately 50 feet deep it costs approximately $2,000 for two people for a bridge located on a small back road. Mr. Townsend also agreed to a methodology involving a minimum acceptable level of performance for each road under the classification of National Highway Institute.
NCHRP 24-25 Page 64 Phase II Appendices Additional Telephone Conversations with State DOT Officials Garland Land, Heavy Bridge Maintenance Engineer, Arkansas DOT: Arkansas DOT officials routinely inspect bridges once every two years. They also plot the profile of the channel once every five years to see the changes due to erosion. If the inspector sees a change of approximately 2 feet during a routine inspection then they increase the frequency of scour monitoring to once a year. If the bridge inspector finds a significant change or if the footing is exposed, they place the bridge in scour critical category, perform scour analysis, adopt a rigorous monitoring approach, and place riprap countermeasures as needed. Typical size of the riprap is approximately 1.5 feet in diameter. If a bridge with an unknown foundation is located in the northeast part of the state then there is a high chance that it is supported on timber piling. They normally provide a concrete cap for the piles or drive new concrete piles to support the bridge in case of scour vulnerability. Bridges located in the northwest side of the state tend to be founded on bedrock and hence are not very susceptible to scour. Wayne Seger, Bridge Inspection and Repair Office, Tennessee DOT: Tennessee DOT officials routinely inspect bridges once every two years. They measure cross sections upstream and down stream of bridges using sounding data to estimate scour depth. In 1990âs they did extensive H&H modeling (using WSPRO) to determine the scour depth and identified bridges that were scour susceptible or scour critical. Once identified, they monitor these bridges more frequently and adopt countermeasures accordingly. Their experience suggests that many bridges with unknown foundation are old and most of them are supported on timber piling. If the scour depth is more than the pile depth the bridge is classified scour critical. If the depth of the footing is unknown then they place riprap
NCHRP 24-25 Page 65 Phase II Appendices countermeasures if the bridge is scour susceptible. The riprap used for scour protection falls into one of the following categories.  Type b: 3 inch to 2.25 feet in diameter placed in 2.5 feet thick blanket with at least 20% by weight is more than 6 inch  Type c: 5 inch to 3 feet in diameter placed in 3.5 feet thick blanket with at least 20% by weight is more than 9 inch In the future they will adopt more advanced countermeasures such as gabions and filter fabric. Tri Buu, Geotechnical Engineer, Idaho DOT: There are approximately 3,200 bridges over streams in Idaho, and approximately 580 of these have unknown foundations. Most of these bridges are maintained by local agencies. They routinely inspect bridges every two years. In 1990 they implemented a scour evaluation program for all bridges in the state. This program involved hiring three companies to do scour analysis for all of their bridges. Several years of data were collected and the results were entered into the HYRISK program, which they used to categorize bridges as ânot vulnerable to scourâ, âscour susceptibleâ, or âscour criticalâ. They rated bridges using NBIS. Scott Christie, Chief Bridge Engineer, Pennsylvania DOT: Pennsylvania DOT officials worked with the USGS to develop a program to maintain bridges for scour vulnerability, which also addressed unknown foundation bridges. We obtained a report (1) from Ms. Julie at USGS that generally describes the field survey requirements. This report focuses mainly on characterizing the soil and identifying any evidence of scour and stream bank or bed erosion. William Kramer, Foundation and Soils Unit Chief, Illinois DOT: They have approximately 300 bridges with unknown foundations, which is approximately 10% of the total number of bridges in Illinois. They studied all of the bridges in their state in the early
NCHRP 24-25 Page 66 Phase II Appendices 1990s, and ranked bridges with unknown foundations into one of five categories regarding scour vulnerability. A systematic maintenance program does not exist but they do monitor their scour critical bridges closely, especially during significant events. They sometimes adopt countermeasures (e.g. riprap) if the field. He said most of the scour critical bridges identified in that study have been replaced. Andrea C. H. Hendrickson, Foundation and Soils Unit Chief, Minnesota DOT: They only have approximately five bridges with unknown foundations. Thus, this is not a major issue for Minnesota. Rick Renna, Florida DOT: FDOT is contemplating developing guidelines for managing their bridges with unknown foundations, and wanted to find out what we are doing for NCHRP. FDOT suggested that soil borings could be used to "back calculate" an unknown foundation. A major concern for FDOT is protection of evacuation routes - they recommend putting a very high priority on evaluating evacuation routes. Mr. Renna also noted that the cost of fixing a bridge is sometimes greater than the cost of replacing the bridge. David Fry, Environmental Management, Virginia DOT: VDOT faces many permitting challenges when installing countermeasures for bridges. They have to obtain a permit from either the Army Corps of Engineers, or the Virginia Marine Resources Commission (VMRC), or both in complex cases. Countermeasures usually involve riprap and occasionally grout bags. If they place riprap, then they usually donât need a permit from the Corps; but if they want to place grout bags, they usually report it to DEQ and get a permit from Corps. However, if the drainage area is more than five square miles, they have to get a permit from VMRC regardless of the counter measure. Lotwick Reese, Hydraulic Engineer, Idaho DOT: Bridges having no plans are considered bridges with unknown foundations. If a plan is available regarding a spread
NCHRP 24-25 Page 67 Phase II Appendices footing and they have information on bottom of the footing, then this is used in their scour analysis. If a foundation is pile-supported and if no information is available to estimate the bottom of the pile, they assume a depth of 10 feet and perform scour analysis. If a conceptual plan is available and as-built information is unavailable, they assume that the structure is built according to the concept plan. Once scour analysis is performed they rate bridges using NBIS. They have not addressed the issue of bridges that have no plans yet. Specific Survey: Traffic Characteristics versus Rebuilding Time One hundred and eleven surveys were e-mailed twice to the AASHTO Subcommittee on Bridges and Structures. Twenty-six responses were collected and tabulated. The responses represent states with diverse geographies, populations, and rural versus urban settings. One response was from a Federal Agency. When asked to estimate the traffic characteristics that were most important in predicting rebuild time, ADT and political pressure were deemed the leading predictors of rebuild time. ADT was ranked first or second in importance by 54% of the respondents. Other leading factors for predicting rebuild time included structure type, length, and bypass length. âOtherâ refers to variables receiving only rare mention or low rank â for example: permit time, loss of toll revenue, right of way access, and weather. The second question asked each respondent to rate the importance of the top ten variables that impact bridge rebuild time in such a way that the sum of the ratings is less than or equal to 100%. This question included other social and economic considerations that were suggested by the preliminary interviews of bridge experts. The availability of funds for bridge construction was the single leading predictor of bridge rebuilding time. Cluster analysis suggests that the second most important factors include ADT, political interest, cost of reroute, and environmental permitting. If ADT, cost
NCHRP 24-25 Page 68 Phase II Appendices of reroute, and political interest are considered dimensions of an average level of service concern, then this question arguably confirms the ratings from the first question. The third question asked the experts if they were aware of any relationships between traffic characteristics and the rebuild time within their jurisdiction. Of the 25 written responses, ten of them said that no formal rules or guidelines are being used to predict rebuild time. Detours were mentioned several times. If reasonable detours exist, rebuilding time is likely to increase. One expert explicitly said that rebuilding time increases if short detours are available. The fourth question focused on accelerated construction. It is assumed that if accelerated construction practices are used, the same variables may be a predictor of bridge rebuilding time. The response to this question confirmed that ADT and user costs are the single most important determinate of rebuilding time. The final question gave participants the opportunity to comment on other factors which influence bridge reconstruction time. Responses included a variety of social, contracting, and procurement issues. One insightful comment mentioned that while higher ADT draws higher staff priority, federal and environmental issues supersede ADT. The following lists the questions asked and a tabulation of the responses. Question: When estimating the time it will take to rebuild bridge lost unexpectedly, please rank the most important variables which impact rebuilding time. (#1 = Most important). If the variable has no impact on rebuild time, please note as ân/aâ. Please rate each variable. Response Tabulation Table 11 lists the response.
NCHRP 24-25 Page 69 Phase II Appendices Table 11 Tabulation of Responses to Importance of Rebuild Time Factors Factor Average Rating Median Rating Rated First or Second ADT 2.35 2 14 Structure type 5.12 5 9 Bypass length 4.04 4 7 Political pressure 4.00 3 6 Functional classification 4.19 3 6 Structure length 4.46 5 5 ADTT 3.85 4 5 Highway system 4.00 2.5 4 STRAHNET highway designation 3.19 1.5 3 Total project cost 5.15 4 2 NBIS bridge length 4.42 1 2 Bridge improvement cost 5.08 4 1 Maintenance responsibility 5.58 4 1 Designated level of service 5.00 5 0 Designated national truck network 3.31 n/a 0 Future ADT 3.77 n/a 0 Route signing 4.31 n/a 0 Question: Please estimate a weight (in the form of a percentage) that each variable has on the total time it will take to rebuild a bridge? (Please make sure the total adds up to 100%). There are 10 variables. Response Tabulation Table 12 lists the response.
NCHRP 24-25 Page 70 Phase II Appendices Table 12 Tabulation of Responses to Weights of Rebuild Time Factors Factor Average Rating Median Rating Availability of funds to perform the work 12.77 10 ADT 11.96 10 Political interest 11.62 10 Cost of reroute (lost time and operating costs) 11.58 10 Environmental permits or conditions 11.42 10 Emergency route designation 9.81 10 Social Factors (e.g. only school access) 9.54 8.5 Availability of workforce, materials or equipment 9.50 5 ADTT 4.96 4 Other -- -- Question: In your state, what is the relationship between traffic characteristics and rebuild time? Are there any decision rules or criteria used to guide or predict rebuild time. Please feel free to attach examples. Response 1  All items in 1 and 2 impact rebuild time  Size and cost have a significant impact  If a major/high cost bridge fails it will be a high priority to replace  Securing rebuilding funds takes time  Actual rebuilding times are based on past experience with other structures Response 2  Traffic characteristics dictate the construction.  Political pressure is a factor in low vol. bridge construction Response 3  No hard and fast rules  When a bridge fails it is an emergency  The greater the ADT the greater the intensity of effort to restore service Response 4  Not having many short detour options makes rebuilding time very important
NCHRP 24-25 Page 71 Phase II Appendices  Traffic characteristics would rarely play a role in rebuild time. Response 5  Rebuild time increases if detours are short 3 miles or less  Rebuild time is inversely proportional to ADT  Human and $$ resources are available to solve the traffic and structure wrt to ADT and classification  $$$ is directly related to ADT Response 6  Case by case decision Response 7  No established rules. Strive to provide bypass within a month for routes with long bypass. Traffic characteristics come into play when rebuild is considered. Response 8  There are no rules. In recent experience bridges lost unexpectedly were replaced on fast track Response 9  The heavier the traffic the sooner the rebuild Response 10  No rules to predict rebuild time, to my knowledge Response 11  If traffic is detoured, rebuild time goes down. Response 12  Traffic characteristics not much impact on rebuild time. It is primarily based on size and type of structure. Response 13
NCHRP 24-25 Page 72 Phase II Appendices  Donât know Response 14  No rules in NM for rebuild time Response 15  Traffic volumes linked to revenue for toll roads. Rev loss will push for faster rebuild time.  Need to consider LOS impact on reroutes  Rebuild based on complexity of structure Response 16  None â replace as fast as Fed and environmental permits allow. Design is small amount of time, getting permits, environmental clearance and rights of way are the problem. Response 17  No rules or criteria Response 18  No rules in place. Criticality to mobility is more important than cost. Response 19  If traffic count was high, accelerated construction activity would be encouraged to get the bridge open as soon as possible. Response 20  No formal guidelines, generally ADT indicates higher importance of the bridge. We would therefore consider it urgent to restore service to a high ADT bridge. Response 21  (Army) as a federal agency we are not involved in a lot of bridge rebuilding and have not established these relationships. We will usually defer to the local states.
NCHRP 24-25 Page 73 Phase II Appendices Response 22  To date we have not developed any relationships between traffic characteristics and rebuilding time. Response 23  The more traffic the more political pressure you get to build quickly Response 24  Traffic characteristics are not significant criteria in predicting rebuild time. TX Dot does not have formal criteria in predicting rebuild time. Response 25  We (OH) are working toward a plan development policy concerning maintenance of traffic, accelerated contracts and construction techniques. This tool can be applied to unexpected repair or replacement of bridges. Maintenance of traffic is the engine that drives the process. Question: What determines when accelerated construction techniques would be used? Please list the factors that must be present in order to justify accelerated construction. Response 1  Based on major or high volume structures Response 2  Significant economic impact to regional/local commerce  Adverse impacts on emergency services â hospital access  Length of detour  Total construction time needed Response 2  Three â High ADT, ADTT; long detour; political pressure
NCHRP 24-25 Page 74 Phase II Appendices Response 3  Primarily it is the level of impact the loss has on ADT  User costs and disruption of emergency services are key factors Response 4  Used almost always in AZ due to long detours on most highways Response 5  ADT and functional classification  Capacity and LOS of alt. routes  Funds  Capacity of contractors  Environmental permit delays  Traffic flow delays and LOS, public reaction Response 6  ADT and loss of revenue Response 7  Political pressure and traffic characteristics determine if accelerated construction is warranted. Response 8  Based on Traffic volume and economic impact on surrounding communities and business. Response 9  If the state declares an emergency this leads to Fed funds Response 10
NCHRP 24-25 Page 75 Phase II Appendices  Each project is a case by case. High ADT and political pressure, length and inconvenience of detour, environmental limitations, and public input can drive accelerated construction. Response 11  User costs Response 12  High traffic, emergency access, strategic route Response 13  Whenever public is impacted â acceleration should be considered Response 14  Accelerated construction has been used in NM when recovery time is short, detours are preferred and result in faster rebuild. Response 15  Higher volume with significant revenue losses associated with long rebuild.  Effects on surrounding highway network and local economic considerations. Response 16  Will accelerated construction lead to a quality product, and if time gained is worth anything, road user costs. Response 17  ADT, reroute type, political interests and participation. Response 18  Criticality to mobility, local impact and emergency response, detour availability, feasibility with regard to weather, fabrication time, traffic disruption. Response 19
NCHRP 24-25 Page 76 Phase II Appendices  If bridge was totally out of service, that in itself would encourage accelerated construction. Response 20  High ADT, no available detour to accommodate the traffic, interstate route Response 21  Applicability of bridge design for rapid construction techniques  No reasonable location for temporary bridge  Temporary bridge too expensive  Environmental permits will take too long to secure relative to temp. bridge Response 22  When there is no convenient detour  Emergency vehicle access is delayed  Cost of delay is unacceptable politically or economically Response 23  Factors include user costs, criticality or importance of structure, detour length or availability and cost. Response 24  Maintenance of traffic is the main concern. Balancing the cost of acceleration against the public user cost is still a case by case determination.  Emergencies are typically processed in the following fashion: ⢠Use of type âAâ emergency contracts â no bid, start the same day with time and materials ⢠Lesser âBâ emergencies may be bid on a shortened schedule with a few invited contractors.
NCHRP 24-25 Page 77 Phase II Appendices ⢠Combining type âAâ and âBâ Example demolition and site prep while preparing design and bidding for the bridge construction. ⢠Partnership with designers, suppliers, contractors and the department to cut through most formality. ⢠Drop everything to process project documentation, submittals, and reviews ⢠Use standard construction techniques that everyone knows how to do ⢠Contractor my staff the job to work 24/7 unless this is not effective based upon preordering project materials ⢠Replace the bridge using existing plans to minimize design time. Question: Please list any additional comments about factors which influence the time needed to rebuild bridge lost unexpectedly. Response 1  Maintenance of traffic-longer const times are needed if staged building process Response 2  national security, hurricane evacuation routes and military routes impact time Response 3  Traffic disruption, access to advance construction tech, skilled personnel availability. Construction industry is not oriented to develop Joint Venture solutions and risk mgt tech for this type of project â in PR Response 4  The # of lost bridges in state and in adjacent states determines availability of resources (designers and materials) Response 5  Traffic volume and availability of a detour route
NCHRP 24-25 Page 78 Phase II Appendices Response 6  FHWA Fed Emergency funds are usually 100% above obligation but rebuild must be done within 6 months of event Response 7  Procurement laws/rules can impact design and construction selection Response 8  Political demands fast rebuild time unless there is a reasonable detour nearby. Response 9  Higher ADT draws higher staff priority but Fed Regs and Environmental considerations make no such distinction with respect to ADT/use. Response 10  If route can be closed to traffic, rebuild time can be cut drastically. Response 11  Environmental agency response not as responsive as they need to be. Response 12  Time required is directly related to the length and width of bridge. Also bridges over major rivers will take longer to replace. Response 13  Availability of new or replacement bridge components  Purchase required ROW Response 14  Evaluation/analysis of the reason for losing the bridge  Time required for bridge removal
NCHRP 24-25 Page 79 Phase II Appendices  Whether a temporary bridge is viable (if so a pressure for a replacement bridge my be substantially reduced) Response 15  Funds for contractor incentives, physical location (site difficulties and access) Response 16  Time to design the repair or replacement  Availability of existing plans, hydraulic or foundation data  Availability of mill materials for steel beams or girders  Lead time on fabricated elements: beams, bearings, railings etc  Site access problems: cofferdams, sheeting, placement of cranes etc  Working around the MOT or detour  Time of year  Contractor ability to schedule and devote full capacity to the project
NCHRP 24-25 Page 80 Phase II Appendices Scour-Related Bridge Failure Databases State DOT officials were contacted by telephone during June â July 2005 to ascertain the status and availability of a historical record of scour failures at bridges. These conversations focused on quantifying the historical performance and the designed performance of bridges with regard to scour failure. Table 13 summarizes the results from these conversations. This phone survey discovered that many states had not formally compiled a record that summarized bridge failures (and their cause) on a state-wide scale. Thus, many provided estimates based on their collective memories of bridge failures, which are denoted as âanecdotalâ record types in the table. Some states only record the cause of failure on state-owned bridges, which are denoted as âstateâ bridge owners in the table. Two of the state participants and Sterling Jones of the Federal Highway Administration preferred to estimate an average number of scour failures per year over their tenure, while most preferred to estimate a total number of scour failures over their tenure or their summary record. Furthermore most states have been submitting bridge failure information each year since the late- 1980âs to New Yorkâs Safety and Assurance Program. It is easy to calculate, from this information, the average number of scour failures per year, the annual probability of failure (i.e. average failures per year divided by the number of bridges over water), and the implied return period of scour failure (i.e. the inverse of the annual probability of failure). This analysis shows that â for the 25 states that responded â about 33 (i.e. 32.69 in Table 13) bridges per year fail due to scour. This result yields an annual probability of scour failure of about 0.0002, and an implied return period of failure of about 4,900 years. If this number of scour failures for the 25-state record is scaled by the ratio of 379,788 (the total number of bridges over water in the US) over
NCHRP 24-25 Page 81 Phase II Appendices 160,831 (the number of bridges over water from the 25-state record), this reveals that about 77 bridges per year fail due to scour in the US. Table 13 Summary of state records regarding scour failures at bridges State Record Type Estimated Failures Per Year No. Recorded Failures Record Length (years) No. Bridges Over Waterâ¡ Bridge Owners Included Average No. of Failures Per Year Annual Probability of Failure Implied Return Period (years) AL anecdotal 6 -- 15 14,000 all 6 4.3E-04 2,333 AR anecdotal -- 16* 25 11,463 all 0.64 5.6E-05 17,911 CO anecdotal -- 25 40 5,443 all 0.625 1.1E-04 8,709 GA record -- 60 30 6,847 state 2 2.9E-04 3,424 HI anecdotal -- 5 5 774 all 1 1.3E-03 774 IA anecdotal -- 3 12 2,100 state 0.25 1.2E-04 8,400 ID anecdotal -- 4 10 3,508 all 0.4 1.1E-04 8,770 IL anecdotal -- 3 30 12,000 all 0.1 8.3E-06 120,000 MD record -- 0 20 2,507 all 0 0 -- MN anecdotal -- 1 30 360 all 0.0333 9.3E-05 10,800 MO anecdotal -- 3 10 7,893 state 0.3 3.8E-05 26,310 MS record -- 8* 16 12,299 all 0.5 4.1E-05 24,598 ND anecdotal -- 1 35 300 state 0.0286 9.5E-05 10,500 NH record -- 86 78 1,796 all 1.10 6.1E-04 1,629 NJ record -- 3 26 3,256 all 0.115 3.5E-05 28,219 NM anecdotal 0.25 -- 14 1,591 all 0.25 1.6E-04 6,364 NV record -- 6 20 294 all 0.3 1.0E-03 980 NY record -- 32 85 12,643 all 0.376 3.0E-05 33,583 OH anecdotal -- 2 10 14,000 state 0.2 1.4E-05 70,000 PA anecdotal -- 150 9 15,650 all 16.67 1.1E-03 939 TN record -- 10 38 16,867 all 0.263 1.6E-05 64,095 UT anecdotal -- 3 5 1,749 all 0.6 3.4E-04 2,915 WA record -- 43 82 5,823 all 0.524 9.0E-05 11,104 WV anecdotal -- 4* 15 5,741 all 0.267 4.6E-05 21,529 WY record -- 2 14 1,927 all 0.143 7.4E-05 13,489 US (all above) -- 563.5 27.0 160,831 -- 32.69 2.0E-04 4,921 US recordâ -- -- -- 305,756 -- 27.40 9.0E-05 11,157 US anecdotalâ¡ 25 -- 32 379,788 -- 25 6.6E-05 15,192 *Instance where the state official estimated no scour failures, but the NY record recorded this number of scour failures. â Source: The quasi-national bridge failure database, which is updated and maintained by New Yorkâs Safety and Assurance Program and has failure records for 39 States and Puerto Rico. â¡Source: Sterling Jones of the Federal Highway Administration; a table acquired on June 9, 2005.
NCHRP 24-25 Page 82 Phase II Appendices The following summarizes the questions that were asked of each transportation official: 1. Do you have a database recording scour-related bridge failures (i.e. requiring structural repair or replacement)? ⢠Does it contain: structure ID, year built or age, function classification (NBI 26), and ADT (NBI 29, 30)? ⢠Do you record the cause of failure both state and county bridges? ⢠May we request a copy? ⢠How many bridges (over water) do you monitor for scour-related failures (i.e. state-owned vs. county-owned)? 2. If you do not have a database: ⪠What is your conservative estimate for the average number of scour-related bridge failures per year? ⪠What is your conservative estimate for the largest number of scour-related bridge failures per year? ⪠Do you record the cause of failure both state and county bridges? ⪠Can you give any of the following info for any of the structures: structure ID, year built or age, function classification (NBI 26), and ADT (NBI 29, 30)? 3. How many bridges (over water) do you monitor/record for scour-related failures (i.e. state-owned vs. county-owned)? The following responses were obtained: Paul Liles, State Bridge Engineer, Georgia DOT: No database is available. Paul has been monitoring bridges for 30 years, and he only knew about 2 failures that were not associated with the 500-yr flood in 1994. He also recalled 4 scour-related bridge
NCHRP 24-25 Page 83 Phase II Appendices improvements (riprap and dikes) on local road bridges. The 1994/1995 flood event caused them to replace 47 state and local bridges, and he estimates that FEMA may have replaced 10-20 more county bridges during this event. Thus, the total number or failed bridges for this event is between 57 and 67. He stated that most state bridges are designed to last 50- 100 years, whereas county roads are typically designed to last 25 years. Paul later stated that there are 14,500 state and county bridges in their monitoring program. However, they are only responsible for maintaining 6,600 of those bridges (state bridges). They do not monitor why any of the remaining 7,900 county bridges may have been replaced. Scott Christie, State Bridge Chief, Pennsylvania DOT: No database is available. He suggested that we could submit a request to compile the records, but he doubted that many records are available or accessible. He estimated that ~80% of their bridge closures are due to scour problems, but he did not know how many bridges that percentage represents or how many closures were due to failure versus maintenance. Jim Lane, State Bridge Engineer, New Jersey DOT: They have a database extending to at least 1979 of all state/county bridge failures in a MS Word document, which Jim sent us via e-mail. This database lists a bridge ID, bridge name, year built/failed, bridge material type, and cause of failure. This database lists three failures that were due to flood events. Jim later e-mailed NBI items 26, 29, and 30 for these three bridges. Terry Leatherwood, State Bridge Inspector, Tennessee DOT: They have a database. Terry sent a spreadsheet of failures. Frank Liss, State Hydraulics Engineer, West Virginia DOT: Someone in James Sothenâs office transferred the call to Jim Shook, who transferred it to Frank Liss. No database is available. Jim Shook was not aware of any failures since the early 1990âs, but he suspected that some maintenance work may have occurred. Frank Liss referred us
NCHRP 24-25 Page 84 Phase II Appendices by e-mail to Bill Wolford who handles âscour evaluationsâ and might have better estimates. Mr. Wolford did not respond. Collin Boone, State Hydraulics Engineer, Arkansas DOT: Phil Brand recommended calling Collin Boone. No database is available. Collin couldnât recall any failures, but agreed to contact some bridge inspectors to verify this. He later estimated that no state bridges have failed due to scour within the last ten years. However, they do not monitor local or county roads and he would not guess how many of these roads might be failing due to scour. Collin later said that they monitor 11,463 bridges over water every two years. However, they are only responsible for maintaining 5,500 of those bridges (state bridges). They do not monitor why any of the 5,963 county or local roads may have been replaced. Gary Peterson, State Bridge Engineer, Minnesota DOT: No database is available. He is asking their personnel for better records. He said that some counties say that they fill in 2-3 abutments per year that have partially washed out partly due to debris jams. He doesnât think they have had any structural failures, though. He later reported that one state-owned bridge on a principal arterial failed in the last 30 years. They have 162 bridges with unknown foundations, and have 360 bridges over water totally. Of these, 191 are state owned and 169 are locally owned. Lotwick Reese, State Hydraulic Engineer, Idaho DOT: Tri Buu could recall at least two scour related bridge failures in 10 years. Tri then transferred the call to Lotwick Reese, who could recall 4 bridges that failed due to scour in the past 10 years. One was a US-95 overpass, two more were county-owned roads (1996, 1997), and the last one was an I-15 overpass.
NCHRP 24-25 Page 85 Phase II Appendices Mike Fazio, State Hydraulic Engineer, Utah DOT: Mike recalled that 3 county-owned bridges failed in Jan 2005, which they estimate was due to a 125-yr flood event. He then e-mailed a more detailed list of these failures. Mark Grunert, State Bridge Chief, Nevada DOT: No database is available. Mark recalls 6 bridges that have failed due to scour over the last 22 years. They monitor and record cause of failure for all state and county bridges. Four âmajorâ (500-yr) floods and 2 localized floods (1982/3 and 1983/4) account for the six bridge losses. Two of these failures were US-95 arterial roads, and the rest were collector or local roads. NV currently has 294 bridges over water, and 164 of them are state-owned bridges. Matt OâConner, State Hydraulic Engineer, Illinois DOT: No database is available. Matt is not aware of any state bridge failures, and only a âfewâ county bridges (which are âoff-lineâ) failing due to scour in the last 30 years. He estimates that they have about 4,000 state-owned bridges and about 12,000 total bridges over water. Paul Santoâs retired coworker, State Bridge Design Engineer, Hawaii DOT: Does not know if a database is available. The anonymous (retired) coworker only recalls 3 bridges that were replaced after a flood that occurred about five years ago. He stated that their bridges have naturally strong foundations, and that the 3 bridge failures were wooden structures. This coworker placed a note on Curtis Metudaâs desk, but no one responded. Sterling Jones, Federal Hydraulics Laboratory Manager, Federal Highway Administration: Sterling estimates that on average about 25 bridges fail per year nation-wide, and that there are roughly 500,000 bridges over water nationally. Peggy Johnson, Professor, Pennsylvania State University, Water Resources Engineering: Dr. Johnson estimates that about 150 bridges have failed in PA in the past 9 years due to scour, primarily due to three regional flood events.
NCHRP 24-25 Page 86 Phase II Appendices David Chang, State Hydraulic Engineer, North Carolina DOT: David thinks a database is available. He asked David Beard to call us about the data, but no one responded. Bill Krouse, State Hydraulic Engineer, Ohio DOT: No database is available. They define a bridge as a 10 foot span or more (versus 20 ft or more according to Federal definition). Bill only recalls 2 state-owned bridges that have failed due to scour in the last 10 years, and both failing bridges were 10 foot metal arch bridges. They only monitor state owned bridges (~9,618 over water), and there are an additional 27,834 county and local bridges over water. Mike Sullivan, State Safety and Assurance Representative, New York DOT: They have a database. Mike obtained authorization, and later sent their records for NY. Steven White, State Bridge Records, Colorado DOT: Mr. White agreed to attempt compiling a database, but he was unable to meet our deadline. Steven recalls only 5 canal bridges failing since 1970. They monitor and record the cause of failure of state and county bridges. He also recalled that in the 1965 flood that around 15-20 bridges failed. He said the following in a subsequent e-mail, which also contained some photos. Attached is some of the information I have gotten so far. The photos were of a 5 year scour event (June 3-5, 2005) during a replacement of a check dam that had failed. Other "scour" like problems CDOT is worrying about are sinkholes caused by small (less than 20') culvert failures. We had to close I-70 near Vail in both directions for around 18 hours due to a sinkhole from a failed culvert (loss of section mid-way under I-70 and washing out of fill) about 2 years ago. We have found about 50 minor culverts requiring repair out of around 1200 on I-70 and I-25 in Colorado. We are
NCHRP 24-25 Page 87 Phase II Appendices working on the rest of Colorado Interstates and NHS highways to locate any more over probably the next 3-4 years. Attached are photos of some of these problems. Please go to www.denverpost.com for a report on the 1965 flooding in the 6/16/2005 front-page story. Overall, Colorado has not had major loss of highway bridges with the exception of the 1965-66 floods. Occasionally, we have lost a few small county bridges during flooding, but Colorado in general is a semi-arid state with most of our bridges built later than 1950 with adequate foundations for most flooding events. (knock on wood) Colorado had a 10,000 year flood in 1976 in the Thompson Canyon east of Estes Park. There were several bridges in the canyon, but because of the twisting canyon and location of the bridges and being set into granite bedrock, only one bridge had permanent damage of 1 foot settlement which was repaired by raising the pier cap. That bridge was only recently replaced about 6 months ago. All the other bridges were overtopped, but the flow was turned just upstream into the canyon walls. In fact, we lost roadway sitting on granite 15-20 feet above the normal stream due to the crashing of the water as it was forced to make 90+ degree turns. Over 200 people living and camping in the canyon were lost in the flood that was caused by a midnight rainstorm on the night of July 31 â August 1, 1976. This was right around the centennial day and year of Colorado statehood. George Conner, State Maintenance Engineer, Alabama DOT: No database is available. George says that they always close bridges before they fail due to scour. They have several cases per year where they have to close a local road to add additional braces or supports to keep the bridge functional. In many cases, they choose to post weight-limiting signs to keep the road operational. They have 5,600 state bridges, and ~80% of them are over water. All together, they have 14,000 bridges over water that they monitor.
NCHRP 24-25 Page 88 Phase II Appendices Jim Camp, State Maintenance Engineer, Arizona DOT: No database is available. Jim recollects over the last 15 years that a few bridges each year need some work because they wash out. Most of them just need new rip-rap or fill. He wasnât sure, but he thinks approximately one structure every other year may need to be braced while they fill part of the foundation or abutment. They monitor all NBI listed bridges, and he estimates that they have around 600-800 state bridges over water. He did not know the total number of state and local bridges in his State. David Claman, State Hydraulics Engineer, Iowa DOT: No database is available. David said that they only monitor/record 2,100 state bridges (over water). There are an additional 20,000 bridges over water managed by each county/local government. David remembered three principal arterial bridges that failed since 1993. Two of them occurred in 1998, and another occurred in 1996. He sent two examples of their management plan for bridges with unknown foundations by e-mail (PDF). Warren Bailey, State Bridge Management Engineer, Mississippi DOT: A database is available, but it is large and needs to be queried for scour-related failures to limit the results. Warren agreed to look into how to query the database (for state structures), but did not follow up. A voice message for Fred Hollis to query his database for county/local bridge failures was never answered. Jerry Ellerman, State Bridge Management, Wyoming DOT: No database is available, but they do report their recollections of all bridge failures to NY. Jerry said they monitor both state and local bridges, but he does not know how many. He recalled two scour-related failures, one partial collapse leading to repair in 1997, and one requiring replacement in 1991. Both were county-owned roads. From his copy of the NY-maintained list of all the bridge failures in WY, he determined that they have records of bridge failures in WY dating back to 1980.
NCHRP 24-25 Page 89 Phase II Appendices Prakash Dave, State Bridge Engineer, Maryland DOT: A database is available, but it is large and needs to be queried for scour-related failures to limit the results. He later said that they could not find any recorded failure that was attributed to scour. Dave Powelson, State Bridge Engineer, New Hampshire DOT: Dave had a copy of the national bridge failure record, which is managed by Shawn McAdoo in NY. He also saw historical accounts of flooding in 1927 that resulted in 76 bridge replacements, and of floods in 1936 and 1938 that resulted in âa fewâ replacements. His copy of the NY- maintained record showed that floods caused one bridge in 1984, five bridges in 1987, and one bridge in 1995 to fail. NH has 3,055 bridges over water by state definitions. He said that this record, however, only notes that âfloodsâ caused the bridge replacements. The report does not mention scour specifically. Shawn McAdoo, State Safety and Assurance, New York DOT: Shawn e- mailed their national database of bridge failures (a MS Access database). This database is updated yearly as each state reports all of their bridge failures for that year. At the start of the database (1987), each state was asked to send historical accounts of any past bridge failures that they could recall. This database should not be considered a complete record, and it does not report how many bridges each state has been monitoring. The accuracy of the records in this database depends on the participating States. Cliff Scott, State Bridge Engineer, Wyoming DOT: Cliff recalled only one bridge that failed due to scour since 1970. They only monitor state-owned bridges, and he estimated that there are 2-300 state bridges over water in WY. Ken Foster, State Bridge Inspection Engineer, Missouri DOT: No database is available. Ken estimates that there have been 2-3 state bridge failures due to scour over the last 10 years. He is only aware of 3-4 off-line bridges that have failed due to scour, but
NCHRP 24-25 Page 90 Phase II Appendices he is not confident that this reflects a state-wide off-line number of failures. He stated that Missouri experienced two 500-yr flood events in his tenure, and he does not know off-hand how many state bridges over water that they currently monitor.
NCHRP 24-25 Page 91 Phase II Appendices Other Scour-Related Information State officials were also asked to respond to the following questions: 1. How has the number of bridges (over water) changed over your tenure (i.e. about how many bridges over water did you have at the beginning of your tenure)? 2. When (approximate year) did your state begin designing new bridges for scour? 3. What magnitude flood is used in the scour equation for those bridges? Is it different for different functional classifications (NBI item 26)? 4. When any existing bridge needs scour countermeasures (e.g. rip-rap), what magnitude flood is used in the scour equation to design the countermeasures? Is it different for different functional classifications (NBI item 26)? The following responses were obtained: Paul Liles, State Bridge Engineer, Georgia DOT: Paul said that the number of bridges over water has been relatively constant over the last 30 years. They began designing for scour sometime in the late 1980âs. They design new bridges to withstand the scour from a Q500 flood, but he said that their Q500 is really just the Q100 multiplied by a safety factor. They also design their scour countermeasures based on a Q500. Paul stated that he was not confident that the scour equations really give them 500-yr flood protection. George Conner, State Bridge Maintenance Engineer, Alabama DOT: George estimated that the number of bridges over water has not changed much in 30 years. He said that they started designing for scour after 1991. Eric Christie said that new state bridges are designed for the Q500 and Q100 scour events, but that counties usually do not design for scour. For scour countermeasures, they look at the Q100 scour predictions, which they donât trust, and use engineering judgment (experience) to decide how much is needed. They have about 3000 bridges with unknown foundations, and most of them are county-
NCHRP 24-25 Page 92 Phase II Appendices owned bridges. Eric does not think their counties will heed any scour guidelines in the foreseeable future. Collin Boone, State Hydraulics Engineer, Arkansas DOT: Collin said that the number of bridges over water has increased about 15% since 1992. They have been designing for scour since at least 1989. For scour at new bridges, they look at the Q100 and Q500 and the Qovertop, and choose whichever yields the maximum scour. This is also what they use to design scour countermeasures. Steven White, State Bridge Records, Colorado DOT: Steve estimated that the number of bridges over water has probably increased at a rate of about 40 bridges per year (most of them local bridges). He said that CO started designing scour countermeasures in 1975 to prevent the damage caused by the flood of 1965. CO started using federal guidelines for scour design in 1995, when the coding guide first came out. He said they always look at the scour predicted for the Q100 and the Q500, but in the end they almost always âgo all the way to bedrockâ. For scour countermeasures, they always look at the scour predicted from the Q100 and Q500, but they seldom heed this alone. The decision to use scour countermeasures at all is always weighed in a careful cost-benefit analysis, where they look at the sufficiency rating of the bridge, its life-expectancy, and its functional class and ADT. The cost-benefit analysis usually leads them to replace any older bridges that need countermeasures with better designs. Jerry Ellerman, State Bridge Operations, Wyoming DOT: Jerry estimated that the number of bridges over water has stayed roughly constant over the past 14 years. Bill Bailey said they started designing for scour around 1979, and later adopted federal guidelines. They look at Q100 and Q500 for predicting scour for new bridges. For scour countermeasures, they usually just look at Q100.
NCHRP 24-25 Page 93 Phase II Appendices Jim Camp, State Bridge Maintenance, New Mexico DOT: Jim estimated that there has been a 5% increase in the number of bridges over water in last 14 years. They have been designing for scour since 1991 or 1992. New state bridges are designed according to federal guidelines (using Q100 and Q500). For scour countermeasures, they look at the Q100, but they often deviate from the calculated design numbers based on the history of each bridgeâs performance. Andy Thomas, State Bridge Engineer, Pennsylvania DOT: Andy said they donât keep any records of how many bridges theyâve had historically. He said that they have been designing for scour since at least 1993. For new bridges they look at Q100 with full safety factors and at historically destructive flows. He said that Q500 is almost never conservative enough, and is often ignored. Thus, whichever flow gives them the most predicted scour is what they use in their new bridge designs. The same procedure applies to how they design scour countermeasures. Andrea Hendrickson, State Hydraulics Engineer, Minnesota DOT: Gary Peterson set up a conference call with Andrea. Gary looked at some total bridge statistics and estimated that the number of bridges over water has remained relatively constant over the past 16 years (and may have actually declined slightly). Andrea said that theyâve been designing for scour since at least 1989 (her earliest record on-hand). For new bridges they look at Q100, Q500, and Qovertop to see which of them predicts the most scour. For scour countermeasures, they usually just design them for Q100 (with safety factors). Mike Sullivan, State Hydraulics Engineer, New York DOT: Mr. Sullivan wrote the following in an e-mail. Of the 19,734 bridges in New York State, 12,643 of them are over water (4,023 state- owned (NYSDOT), 8083 local-owned (town, county, etc.), and 537 have the owner
NCHRP 24-25 Page 94 Phase II Appendices listed as "other" as in other bridge authorities (NYS Thruway etc.) or non-DOT state agencies (NYS Dept. of Environmental Conservation, etc.). Of the 12,643 bridges over water, 12,081 are highway bridges over water (3,972- State, 7,775-Local, and 334-Other). Of the 12,081 highway bridges over water, only 766 bridges are currently coded as Scour-Critical for FHWA Item 113 (Item 113 = 0,1,2,or 3). Of the 766 Scour-Critical bridges, only 1 bridge (local-owned) is coded '0' for Item 113, which indicates it has failed and is closed to traffic. The remaining 765 scour- critical bridges are all coded '2' or '3' (37='2', 728='3'). I can't really estimate the growth rate of our bridges. I would guess that the number of bridges over water has remained fairly constant since the early 1970s (after the interstate boom of the 60s). The oldest data I have indicates that there were 12,599 bridges (highway, railroad, and pedestrian) over water in 1994 and 12,616 over water in 1997 - Not much of a growth rate when compared to 12,643 bridges over water in 2005. Responses to other questions are listed below: 1. NYSDOT created its Bridge Safety Assurance Unit shortly after the NYS Thruway bridge collapse in 1987. The first edition of our Hydraulic Vulnerability Manual was issued in 1991. The first edition of HEC-18 was also released in 1991. Therefore, I assume we started formally designing for scour in 1991. I passed these three questions on to our Hydraulic Design Unit but I haven't received a response yet. They may be out in the field. 2. 500-year event for Interstate bridges. 100-year event for all others. 3. 500-year event for Interstate bridges. 100-year event for all others.
NCHRP 24-25 Page 95 Phase II Appendices Terry Leatherwood, State Maintenance Engineer, Tennessee DOT: Mr. Leatherwood wrote the following in an e-mail. We only have records going back to 1982. However, I can give you 2 or 3 data points. In December of 1982, Tennessee had 17,554 bridges. This total broke down to 5,360 system (state maintained) and 12,194 off-system (local) bridges. In March of 1990, Tennessee had 18,711 bridges. This total broke down to 7,023 system (state maintained) and 11,688 off-system (local) bridges. In May of 2000, Tennessee had 18,994 bridges. This total broke down to 7,898 system (state maintained) and 11,096 off-system (local) bridges. The Statewide Summary report, that I e-mailed to you the other day, contains totals on the current number of public highway bridges in Tennessee. The above figures are for the TOTAL number of bridges. Our records (from years ago) do not break out bridges over waterways versus other types. So, I can't give you exact figures for that. However, if you look at our current numbers you see that: Percentage of system bridges over waterways = (6,446 / 8,071) X 100 = 79.866 % Percentage of off-system bridges over waterways = (10,421 / 11,361) X 100 = 91.726% You could assume that these percentages have remained constant (which I think is mostly true) and multiple the above bridge count figures by these percentage numbers to estimate the number of bridges over waterways for each data point. While we had some procedures for the hydraulic design of bridges dating all the way back to the 1920's and 1930's, we did not really get serious about scour design until the Hatchie River Bridge failure in the Spring of 1989. This failure resulted in 8 deaths and was investigated by the National Transportation Safety Board (NTSB). It really showed us that our bridge scour design process could and should be improved. We took steps to improve our design process starting in 1989.
NCHRP 24-25 Page 96 Phase II Appendices Our current hydraulic design procedures are available on-line at the following URL: http://www.tdot.state.tn.us/Chief_Engineer/assistant_engineer_design/structures/th mall.pdf You may want to especially read Memorandum 08 starting on page 49. All System bridges are checked for the 100 yr. flood and at the 500-yr level as well. This is because the maximum 500-yr event may not necessarily generate the maximum scour. For off-system (local) bridges, it varies depending upon the program under which the bridge is built. Basically, a local bridge is usually built in one of 3 ways in Tennessee. 1) The local owner can decide to build the bridge using local funding only (i.e. no State or Federal funding is used). In this case, the scour design of the bridge is totally in hands of the designer (it could be a consulting engineering firm or a county/city engineer) selected by the local owner. As we say in Tennessee, TDOT "has no dog in this hunt". However, most consulting engineering firms would follow TDOT Guidelines as a "good practice". 2) The Tennessee Dept. of Transportation (TDOT) has a program to use Federal Highway funds to help local owners replace bridges. If the local owner chooses to use this program, he pays 20% of the cost with 80% being Federal funding. The bridge is designed by TDOT engineers. TDOT also lets the construction contract and provides construction inspection. Basically, in this case, the bridge is treated exactly as if it was a System bridge. The only difference is that the local owner assumes maintenance responsibility for the new bridge once it is built. 3) TDOT also has a second program that uses State Aid funding (A.K.A. Grant Program Funding) to help local owners replace bridges. These are typically small
NCHRP 24-25 Page 97 Phase II Appendices bridges and culverts on local, low ADT routes. Under this program, the local owner hires an engineering firm to design the bridge and provide construction inspection. The design plans are submitted to TDOT for review and approval before the local owner lets the contract. These "Grant" bridges are not usually designed, hydraulically, for the full 100 yr. event. Our general requirement is that the hydraulic design must be an improvement over the existing bridge that is being replaced. However, the bridge is still checked for scour at the upper 100 yr. and 500 yr. levels. As above, this depends upon if the bridge is a System bridge or an Off-System bridge. For a System bridge, the TDOT Hydraulic Office designs the scour countermeasures in accordance with our established design procedures as outlined above. However, TDOT is not responsible for maintenance for local (Off-System) bridges. This is by Tennessee Law as listed below: Tennessee Code Annotated Section 54-1-126: Responsibility for maintenance of public roads, streets, highways or bridges. (a) The department of transportation is responsible for the maintenance of only those public roads, streets, highways or bridges and similar structures which are designated by the department as being on the state system of highways or the state system of interstate highways. (b) The department shall enter into a written contract with each city, county, or metropolitan government before undertaking any work or providing any funds for work with respect to public roads, streets, highways or bridges and similar structures, within their boundaries, other than those designated by the department as being on the state system of highways or the state interstate system of highways.
NCHRP 24-25 Page 98 Phase II Appendices These contracts shall include a provision that such city, county or metropolitan government is solely responsible for all maintenance of the completed work. No such contract shall be valid in the absence of such maintenance provision. So, while TDOT can recommend that a local bridge owner install scour countermeasures, it is the TOTAL responsibility of the local owner to follow through on our recommendations. The type of countermeasure installed is solely the decision of the local owner and whatever engineer he chooses to use or hire for the job. Lotwick Reese, State Hydraulics Engineer, Idaho DOT: Lotwick estimated that the number of bridges over water has stayed roughly constant over the past 10 years. He said they started designing for scour around the early 1980âs, and later adopted federal guidelines. They look at Q500 and Qovertop for predicting scour for new bridges. The same applies to how they design scour countermeasures. Bill Krouse, State Hydraulics Engineer, Ohio DOT: They started designing for scour after the Schoharie collapse, presumably like all the States. Before that they used a more common sense approach. They have not used spread footings on scour-prone soils for probably 25 years or more. James Lane, State Bridge Engineer, New Jersey DOT: There were 825 bridges over waterways in 1983. Specific criteria for scour design were instituted in 1998. The criteria used prior to that date were less specific. They use Q100 in new bridge scour design and in scour countermeasure design.
NCHRP 24-25 Page 99 Phase II Appendices Management-Related Information Sate officials were asked the following questions: 1. What criteria do you use to identify a bridge over water with an unknown foundation as scour-critical or at-risk, and what methods did you use to evaluate these criteria? 2. Once a bridge with an unknown foundation is identified as scour-critical or at- risk, what monitoring and/or action plan do you use? The following responses were obtained: Sharon Slagle, State Bridge Design, Texas DOT: Ms. Slagle wrote the following in an e-mail. Thank you for your interest in our bridge scour program. You can read TxDOT policy on scour in our online manuals, particularly the following: * Hydraulic Design Manual * Bridge Inspection Manual * Geotechnical Manual Mark McClelland can answer specific questions you have about Texas bridge foundations, and you can reach him most effectively by e-mail at [omitted]. David Claman, State Bridge Maintenance, Iowa DOT: David said that Iowa goes to all of their bridges with unknown foundations and measure any scour holes present at these bridges (during their routine inspection every 2 years). They are reasonably confident that all of their piles are 20 feet or longer. If they discover a scour hole that is five feet or less, they assume that the bridge is scour safe. If they discover a scour hole exceeding 5 feet in depth, they label it scour critical (currently applies to 180-190 bridges). Once a bridge is labeled such, the bridge is inspected during and after any flood peak that
NCHRP 24-25 Page 100 Phase II Appendices exceeds the âcritical water markâ assigned to that bridge. To select the critical water mark, they perform an H&H study of the underlying waterway, which usually entails monitoring after any event greater than the 25-yr flood. During a âcriticalâ flood they close the bridge, and use sonar to monitor the berms and bed before opening the bridge again. Iowa will soon begin using an online âScour Watchâ system to monitor â in real-time â all of their scour critical bridges. David said that Tennessee, New York, Connecticut, and Iowa are also planning to use this system. Terry Leatherwood, State Bridge Inspector, Tennessee DOT: Mr. Leatherwood wrote the following in an e-mail. As for the Scour Watch program, yes, we are in the process of implementing it. We plan to use the scour watch program to monitor all scour critical bridges (as defined by NBI Item 113 being coded as 3 or less) irrespective of whether the bridge has unknown foundations or not. We have already completed a process where we screened all of our bridges into "low risk" or "at risk" categories. Most culvert type structures and bridges with foundations solidly set in bedrock were classified as "low risk". We then took the "at risk" bridges and ran an analysis to determine a coding value for NBI Item 113. Our procedure for these "at risk" bridges was as follows: PROCEDURE: The drainage area of the stream at the bridge site was calculated. Usually this was done using U.S.G.S. quadrangle sheets. Then the TDOT QCALC software program was used to compute theoretical discharges for the 100 year flood event. Depending upon the functional class of the route, we sometimes looked at other return frequencies as well. For example, on local county roads, we often looked at lower frequencies down to a 2 year return period. On higher functional class routes, we would sometimes check the 500 year return in addition to the 100 year return
NCHRP 24-25 Page 101 Phase II Appendices period. However, the main coding decision for Item 113 was based upon the 100 year return frequency. Using these discharges, field surveys of the site, and hydraulic parameters from published sources and field observation; a hydraulic analysis of the steam crossing was done using the WSPRO software program. The output from this analysis provided theoretical water surface elevations and velocities which were then incorporated into software using methodology contained in the HEC-18 manual to predict theoretical scour lines for the structure. The theoretical scour conditions were then evaluated using available data on the structure and certain engineering assumptions to provide an assessment as to the site's vulnerability to scour and to make a recommendation for the coding of NBI Item 113. Most of our "at risk" bridges with unknown foundations consist of timber pile supported structures. For these bridges, the lengths of the timber piles are unknown. In this case, we simply assumed that the length of the piles would not exceed 30 feet and based our scour assessment upon this assumption. This assumption may, or may not, be conservative but it seemed reasonable to us at the time. Our main "Plan of Action" for these scour critical bridges is to just monitor them with the Scour Watch system until they can be replaced with new bridges designed to modern standards. For System bridges, we may also install various types of scour countermeasures (such as rip-rap or gabion beds, etc.) if we feel they are needed. We are forbidden, by Tennessee law, to do any maintenance work on local (County or City owned) bridges. We will, however, issue recommendations to local bridge owners to install scour countermeasures if we believe they are needed. However, it is entirely the responsibility of the local owners to follow through on our
NCHRP 24-25 Page 102 Phase II Appendices recommendations. We have no legal authority to "make" the local bridge owner comply with our recommendations. The only thing we can do is order the bridge weight posted or closed if we judge it to be unsafe for legal loads. If the local owner fails to comply with a Weight Posting or Closure order, we shut off all Federal Highway funding to that owner until he does. References 1. Cinotto, P. J. and K. E. White. Procedures for Scour Assessments at Bridges in Pennsylvania. Open-file report 00-64, Pennsylvania Department of Transportation, Lemoyne, PA, 2000.
NCHRP 24-25 Page 103 Phase II Appendices APPENDIX D. ANNUAL PROBABILITY OF SCOUR FAILURE AND MINIMUM PERFORMANCE LEVELS There are two changes that are designed to make the original HYRISK method more applicable to managing bridges with unknown foundations. The first basic change involves scaling the annual probabilities down to a level that corresponds better to the recorded number of bridges that have failed due to scour. The first change primarily improves prediction of the risk factor in HYRISK, but it also improves our understanding of bridge performance. Thus, the second change involves introducing minimum performance levels that hold bridges with higher importance to a higher performance standard than less- important bridges. HYRISK Probability Adjustments The scour-related bridge failure interviews (see Appendix C) with State transportation agencies lead to an estimate of approximately 33 failures per year for the 25 States interviewed (i.e. 33 out of about 161,000 bridges). This suggests that the annual average probability of failure is 33/161,000 = 0.000206, or about 1 in 5,000 per year. Scaling this to all bridges over water (i.e. 379,788) yields almost 80 scour failures per year. Many of the NCHRP panel members believe that the number of scour failures is probably under- reported, particularly for non-State-owned bridges. This belief is partly substantiated by the fact that the quasi-national bridge failure database maintained by NY recorded a few more scour failures in Arkansas, Mississippi, and West Virginia than the interviewed state officials could find in their records or collective memory. Thus, given the nature of the uncertainty in any of these ârecordsâ a more conservative estimate of the number of scour failures might be about 100 per year. If the original HYRISK method (see tables in Appendix A) is applied to all of the bridges over water in the NBI database (i.e. 356,378 bridges, as of the end of 2005), this
NCHRP 24-25 Page 104 Phase II Appendices analysis yields about 60,511 failures per year (i.e. the sum of the probabilities of failure for all 356,373 bridges). This corresponds to an annual average probability of failure of 0.17, and implies that about 1 in 6 bridges fail per year due to scour. These assumptions clearly do not correspond with the experience cited earlier, and result in exaggerated risk factors. Note that this was not a problem within the context of the original HYRISK methodology because HYRISK was primarily used to prioritize bridges. However, when using risk to set a course of action (guidelines), it is important that risk be as accurate as possible in order to properly account for costs and benefits of various management activities. For this reason, all of the original HYRISK failure probabilities have been scaled down to a level corresponding to the approximate number of failures (nation-wide) obtained from the State interviews. Figure 7 shows how the probabilities of failure in the original HYRISK method were adjusted in three basic steps. Each step is represented by a new row of tables in this figure. Each table shows information versus scour vulnerability and overtopping frequency. The first table in each row shows the probabilities of failure, which is adjusted in each successive row of the figure. The second table in each row shows how many bridges in the 2005 NBI database correspond to each level of scour vulnerability and overtopping frequency â in other words, this table results from applying Tables 2 and 3 (Appendix A) to each bridge in the 2005 NBI database. The third table in each row is the product of the corresponding entries in the first and second tables in each row â in other words, this table shows the number of scour failures per year implied by the probabilities of failure. The first row in this figure shows the result of applying the original HYRISK probabilities to the bridge population â in other words, the original HYRISK probabilities imply that about 60,511 bridges fail each year due to scour. The second row in the figure shows the result of multiplying the original HYRISK probabilities by 0.00121
NCHRP 24-25 Page 105 Phase II Appendices (0.000206/0.1698), which effectively reduces the total number of scour failures per year to about 73 per year. The third row in the figure shows the effect of adjusting the probabilities of failure for scour vulnerabilities equal to 1 through 4. To understand this adjustment, recall that any bridge with a low scour vulnerability rating is more vulnerable to scour than a bridge with a high scour vulnerability rating. Thus, this adjustment basically assumes that bridges with a scour vulnerability of 4 or less are probably more likely to fail than the result of the first adjustment â in other words, this adjustment raises the total number of scour failures to about 117 per year. The fourth and final row in the figure shows the effect of rounding off most of the probabilities to two significant digits and recognizing that any bridge with a scour vulnerability rating equal to 0 means that it has already failed. The final adjustment in (the fourth row) in Figure 7 shows that the adjusted probabilities of failure imply that about 109 bridges fail per year due to scour, which is a little more conservative than the interviews regarding bridge failure indicated. However, these probabilities are much more consistent with experience than the original HYRISK method, and thus should yield much more reasonable risk factors. Thus, these are the probabilities used in the âScour Risk Management Guidelinesâ section of the report. Figure 8 plots these probabilities of failure versus scour vulnerability and overtopping frequency in a way that should help the reader understand the next section better. Note that scour vulnerability is displayed along the x-axis, while overtopping frequency is displayed with different symbols, which are explained in the legend. It should be noted again that the inverse of annual probability of failure has the same units as a return period, but this should not be confused with the expected design life of a bridge (see âPerformance-Based versus Traditional Design Practiceâ in the Introduction). In other words, the probability of failure is a measure of the expected performance of a bridge; but its inverse is not an explicit measure of its expected design life.
NCHRP 24-25 Page 106 Phase II Appendices Original HYRISK Assumptions Probability of Failure 2005 Bridge Population Number of Failures Remote Slight Occasional Frequent Remote Slight Occasional Frequent Total Remote Slight Occasional Frequent TOTAL 0 1 1 1 1 0 15 185 209 61 470 0 15 185 209 61 470 1 1 1 1 1 1 6 115 119 31 272 1 6 115 119 31 271 2 0.4573 0.4831 0.628 0.7255 2 100 1116 1289 255 2762 2 45.73 539.1396 809.492 185.0025 1579.364 3 0.2483 0.2673 0.3983 0.4951 3 281 2869 3138 268 6559 3 69.7723 766.8837 1249.8654 132.6868 2219.208 4 0.1266 0.1373 0.2277 0.2977 4 1326 12668 10720 649 25367 4 167.8716 1739.316 2440.944 193.2073 4541.339 5 0.00522 0.00648 0.0314 0.05744 5 2286 22088 18083 689 43151 5 11.93292 143.1302 567.8062 39.57616 762.4455 6 or U 0.18745 0.2023 0.313 0.3964 6 8264 71173 26799 776 107018 6 1549.087 14398.3 8388.087 307.6064 24643.08 7 0.18745 0.2023 0.313 0.3964 7 14574 88828 15754 439 119602 7 2731.896 17969.9 4931.002 174.0196 25806.82 8 0.00312 0.00368 0.0144 0.02784 8 8046 31874 3973 83 43984 8 25.10352 117.2963 57.2112 2.31072 201.9218 9 0.00208 0.00216 0.0036 0.006 9 3909 2927 378 15 7238 9 8.13072 6.32232 1.3608 0.09 15.90384 TOTAL 38807 233843 80462 3266 356378 TOTAL 4630.524 35980.29 18773.7686 1126.499 60511.08 0.169795 Direct Scaling Assumptions (scaling = actual P(f)/HYRISK P(f) = 0.000206/0.1698 Probability of Failure 2005 Bridge Population Number of Failures Remote Slight Occasional Frequent Remote Slight Occasional Frequent Total Remote Slight Occasional Frequent TOTAL 0 0.001213192 0.001213192 0.001213192 0.001213192 0 15 185 209 61 470 0 0.018198 0.224441 0.25355713 0.074005 0.5702 1 0.001213192 0.001213192 0.001213192 0.001213192 1 6 115 119 31 272 1 0.007279 0.139517 0.14436985 0.037609 0.328775 2 0.000554793 0.000586093 0.000761885 0.000880171 2 100 1116 1289 255 2762 2 0.055479 0.65408 0.98206921 0.224444 1.916072 3 0.000301236 0.000324286 0.000483214 0.000600651 3 281 2869 3138 268 6559 3 0.084647 0.930377 1.51632669 0.160975 2.692326 4 0.00015359 0.000166571 0.000276244 0.000361167 4 1326 12668 10720 649 25367 4 0.20366 2.110125 2.96133371 0.234398 5.509516 5 6.33286E-06 7.86148E-06 3.80942E-05 6.96857E-05 5 2286 22088 18083 689 43151 5 0.014477 0.173644 0.68885793 0.048013 0.924993 6 or U 0.000227413 0.000245429 0.000379729 0.000480909 6 8264 71173 26799 776 107018 6 1.87934 17.4679 10.17636 0.373186 29.89678 7 0.000227413 0.000245429 0.000379729 0.000480909 7 14574 88828 15754 439 119602 7 3.314315 21.80094 5.98225213 0.211119 31.30863 8 3.78516E-06 4.46455E-06 1.747E-05 3.37753E-05 8 8046 31874 3973 83 43984 8 0.030455 0.142303 0.06940817 0.002803 0.24497 9 2.52344E-06 2.62049E-06 4.36749E-06 7.27915E-06 9 3909 2927 378 15 7238 9 0.009864 0.00767 0.00165091 0.000109 0.019294 TOTAL 38807 233843 80462 3266 356378 TOTAL 5.617715 43.651 22.7761857 1.36666 73.41156 Scaling assumptions with adjustments to SV = 1 through 4 Probability of Failure 2005 Bridge Population Number of Failures Remote Slight Occasional Frequent Remote Slight Occasional Frequent Total Remote Slight Occasional Frequent TOTAL 0 0.01 0.02 0.02 0.02 0 15 185 209 61 470 0 0.15 3.7 4.18 1.22 9.25 1 0.01 0.01 0.01 0.01 1 6 115 119 31 272 1 0.06 1.15 1.19 0.31 2.71 2 0.005 0.006 0.008 0.009 2 100 1116 1289 255 2762 2 0.5 6.696 10.312 2.295 19.803 3 0.0011 0.0013 0.0016 0.002 3 281 2869 3138 268 6559 3 0.3091 3.7297 5.0208 0.536 9.5956 4 0.0004 0.0005 0.0006 0.0007 4 1326 12668 10720 649 25367 4 0.5304 6.334 6.432 0.4543 13.7507 5 6.33286E-06 7.86148E-06 3.80942E-05 6.96857E-05 5 2286 22088 18083 689 43151 5 0.014477 0.173644 0.68885793 0.048013 0.924993 6 or U 0.000227413 0.000245429 0.000379729 0.000480909 6 8264 71173 26799 776 107018 6 1.87934 17.4679 10.17636 0.373186 29.89678 7 0.000227413 0.000245429 0.000379729 0.000480909 7 14574 88828 15754 439 119602 7 3.314315 21.80094 5.98225213 0.211119 31.30863 8 3.78516E-06 4.46455E-06 1.747E-05 3.37753E-05 8 8046 31874 3973 83 43984 8 0.030455 0.142303 0.06940817 0.002803 0.24497 9 2.52344E-06 2.62049E-06 4.36749E-06 7.27915E-06 9 3909 2927 378 15 7238 9 0.009864 0.00767 0.00165091 0.000109 0.019294 TOTAL 38807 233843 80462 3266 356378 TOTAL 6.797951 61.20216 44.0533291 5.450531 117.504 To be conservative, do not scale down Scour Vulnerability = 0. Assume P(F) for these is 1 and do not count against annual expectation, because these have already failed. This is conservative. Final Result: Scaling, adjustments, and rounding Probability of Failure 2005 Bridge Population Number of Failures Remote Slight Occasional Frequent Remote Slight Occasional Frequent Total Remote Slight Occasional Frequent TOTAL 0 1 1 1 1 0 15 185 209 61 470 0 15 185 209 61 470 1 0.01 0.01 0.01 0.01 1 6 115 119 31 272 1 0.06 1.15 1.19 0.31 2.71 2 0.005 0.006 0.008 0.009 2 100 1116 1289 255 2762 2 0.5 6.696 10.312 2.295 19.803 3 0.0011 0.0013 0.0016 0.002 3 281 2869 3138 268 6559 3 0.3091 3.7297 5.0208 0.536 9.5956 4 0.0004 0.0005 0.0006 0.0007 4 1326 12668 10720 649 25367 4 0.5304 6.334 6.432 0.4543 13.7507 5 0.000007 0.000008 0.00004 0.00007 5 2286 22088 18083 689 43151 5 0.016002 0.176704 0.72332 0.04823 0.964256 6 or U 0.00018 0.00025 0.0004 0.0005 6 8264 71173 26799 776 107018 6 1.48752 17.79325 10.7196 0.388 30.38837 7 0.00018 0.00025 0.0004 0.0005 7 14574 88828 15754 439 119602 7 2.62332 22.207 6.3016 0.2195 31.35142 8 0.000004 0.000005 0.00002 0.00004 8 8046 31874 3973 83 43984 8 0.032184 0.15937 0.07946 0.00332 0.274334 9 0.0000025 0.000003 0.000004 0.000007 9 3909 2927 378 15 7238 9 0.009773 0.008781 0.001512 0.000105 0.020171 TOTAL 38807 233843 80462 3266 356378 TOTAL 20.5683 243.2548 249.780292 65.25446 578.8579 TOTAL w/o already failed bridges (0) 108.8579 0.000305 Scour Vulnerability Scour Vulnerability Scour Vulnerability Overtopping Frequency Overtopping Frequency Overtopping Frequency Scour Vulnerability Scour Vulnerability Scour Vulnerability Overtopping Frequency Overtopping Frequency Overtopping Frequency Scour Vulnerability Overtopping Frequency Scour Vulnerability Overtopping Frequency Scour Vulnerability Overtopping Frequency Scour Vulnerability Overtopping Frequency Overtopping FrequencyScour Vulnerability Scour Vulnerability Overtopping Frequency Figure 7 Scaling and adjustment of the HYRISK annual probability of failure table
NCHRP 24-25 Page 107 Phase II Appendices 0.000001 0.00001 0.0001 0.001 0.01 1 2 3 4 5 6 7 8 9 Scour Vulnerability A n n u a l P r o b a b i l i t y o f F a i l u r e 100 1,000 10,000 100,000 1,000,000 R e t u r n P e r i o d , 1 / P a ( y e a r s ) Frequent Occasional Slight Remote R2 Rasdfasdfsdf Series12 Series13 Overtopping Frequency: Figure 8 Final annual probability of failure estimates
NCHRP 24-25 Page 108 Phase II Appendices Minimum Performance Levels The scour guidelines also include minimum performance levels (MPL) for bridges with unknown foundations. MPLs are designed to ensure that any bridge with an unknown foundation and a high (estimated) annual probability of scour failure is automatically selected for foundation reconnaissance to determine the foundation and obtain a scour assessment. Given the uncertainty associated with predicting the scour vulnerability of a bridge with an unknown foundation, the MPL for such bridges should be a function of bridge importance â i.e. functional classification (NBI item 26). One important consideration regarding the selection of MPLs is that the bridge failure interviews indicated that the average annual probability of scour failure nation-wide is approximately 0.0002. Thus, important bridges (e.g. principal arterials) might be held to a minimum performance greater than 0.0002, while less important bridges (e.g. locals) might suffice with a minimum performance less than 0.0002. This is the basic premise behind the MPLs given in Table 14, which are used in the scour guidelines. Table 14 Minimum Performance Levels for Bridges NBI Code Description Minimum Performance Level (Threshold Probability of Failure) Rural 01, 02 Principal Arterial â All 0.0001 06, 07 Minor Arterial or Major Collector 0.0005 08 Minor Collector 0.001 09 Local 0.002 Urban 11, 12, 14 Principal Arterial â All 0.0001 16 Minor Arterial 0.0002 17 Collector 0.0005 19 Local 0.002 Any bridge with an unknown foundation and an annual probability of failure greater than or equal to than the corresponding MPL in this table should be enrolled in the safest management plan, starting with foundation reconnaissance to determine the foundation.
NCHRP 24-25 Page 109 Phase II Appendices Figure 9 shows these MPLs within the context of Figure 8 according to NBI item 26 â functional classification. In other words, any bridge that has a probability of failure below the corresponding MPL line in Figure 9 meets the MPL. Note that meeting the standard set by a MPL in this context simply means that a bridge meets the minimum standard for its classification or importance. Such bridges may still have a risk of failure that prompts the scour guidelines to recommend additional action. Finally, Figure 10 shows the MPLs in Figure 9 superimposed on Figure 8. This figure shows how the MPLs relate to the annual probabilities of failure. For example, this figure shows that a rural minor arterial â NBI item 26 = â06â â must have an annual probability of failure less than 0.0005 in order to meet the MPL. The figure also shows that this means that a rural minor arterial will only pass the minimum standard if any of the following conditions are true:  Scour vulnerability = 5, 8, or 9  Scour vulnerability = 6 or 7, and overtopping frequency â frequent  Scour vulnerability = 4, and overtopping frequency = remote Similarly, a rural minor collector â NBI item 26 = â08â â only passes the MPL if its scour vulnerability is greater than 3, while any principal arterial only passes the MPL if its scour vulnerability is equal to 5, 8 or 9.
NCHRP 24-25 Page 110 Phase II Appendices 0.000001 0.00001 0.0001 0.001 0.01 1 2 3 4 5 6 7 8 9 Scour Vulnerability A n n u a l P r o b a b i l i t y o f F a i l u r e 100 1,000 10,000 100,000 1,000,000 R e t u r n P e r i o d , 1 / P a ( y e a r s ) R2 01,02,11,12,14 16 06,07,17 08 09,19 RasdfasdfsdfMPL for NBI item 26: Figure 9 Minimum performance levels for each functional classification
NCHRP 24-25 Page 111 Phase II Appendices 0.000001 0.00001 0.0001 0.001 0.01 1 2 3 4 5 6 7 8 9 Scour Vulnerability A n n u a l P r o b a b i l i t y o f F a i l u r e 100 1,000 10,000 100,000 1,000,000 R e t u r n P e r i o d , 1 / P a ( y e a r s ) Frequent Occasional Slight Remote R2 01,02,11,12,14 16 06,07,17 08 09,19 Rasdfasdfsdf Series12 Series13 Overtopping Frequency: MPL for NBI item 26: Figure 10 Annual probability of failure and minimum peformance levels
NCHRP 24-25 Page 112 Phase II Appendices APPENDIX E. NON-DESTRUCTIVE EVALUATION Introduction It is anticipated that guidelines for managing bridges with unknown foundations will likely include some investigation of the foundation to eliminate as much uncertainty as possible. Therefore, the literature search included information on non-destructive evaluation techniques that could be employed to provide at lease some additional information on the type and depth of unknown bridge foundations. The National Cooperative Highway Research Program (NCHRP) 21-5 project âDetermination of Unknown Subsurface Bridge Foundationsâ (1) and the NCHRP 21-5(2) project âUnknown Subsurface Bridge Foundation Testing" (2) were performed to evaluate and develop existing and new technologies that can determine unknown subsurface bridge foundation depths. The NCHRP 21-5 Phase I research focused on the identification of potential NDE methods for determining depths of unknown bridge foundations at 7 bridges in Colorado, Texas and Alabama. The NCHRP 21-5 (2) Phase II research focused on evaluating the validity and accuracy of the identified NDE methods for determining depths of unknown bridge foundations. In this phase, 21 bridge sites were studied in North Carolina, Minnesota, New Jersey, Michigan, Oregon, Massachusetts and Colorado. Phase II research also involved the development of hardware and software needed to perform the NDE testing. Please note that this section is intended to provide a simple, quick summary of the most important findings of the NCHRP 21-5 and 21-5(2) research. Full details of the findings, including additional data and full discussions of methods, test locations, etc., can be found the in the final reports for each of these stages of the research. The research found that the borehole Parallel Seismic (PS) and surface Ultraseismic (US) methods were the most applicable methods for determining unknown foundation depths. A number of other NDE methods were also investigated in the research and found
NCHRP 24-25 Page 113 Phase II Appendices to have more limited applications. These more limited NDE methods are also discussed herein and include the Sonic Echo/Impulse Response (SE/IR), Bending Waves (BW), Spectral Analysis of Surface Waves (SASW) surface methods and the Induction Field (IF) and Ground Penetrating Radar (GPR) borehole methods. Although the Crosshole Tomography method used for imaging of drilled shaft foundation defects was discussed during the NCHRP research, due to budget limitations and the requirement for two or more borings this method was not researched at that time. It is discussed herein for completeness as it has since been applied to the unknown foundation problem. Surface NDE Methods Brief discussions of the surface-based Sonic Echo/Impulse Response, Bending Wave, Ultraseismic, and Spectral Analysis of Surface Waves NDE methods for determination of unknown bridge foundation depths are presented below.
NCHRP 24-25 Page 114 Phase II Appendices Sonic Echo/Impulse Response (SE/IR) Test In the Sonic Echo/Impulse Response test (see Figure 11), the source and receiver are placed on the top and/or sides of the exposed pile or columnar the following figure. The depth of the reflector, e.g., a pile bottom, is calculated using the identified sound (compression) wave echo time(s) for SE tests, or resonant peaks for IR tests due to the applied source impact. Figure 11 Surface echo tests
NCHRP 24-25 Page 115 Phase II Appendices Bending Wave (BW) Test The Bending Wave (BW) test (see Figure 12) is based on the dispersion characteristics and echoes of bending waves traveling along very slender members like piles. The method was first developed for timber piles. The method involves mounting two horizontal receivers a few feet apart on one side of an exposed pile, and then impacting the pile horizontally on the opposite side of the pile a few feet above the topmost receiver in an attempt to identify an echo of bending wave energy from the pile tip as shown in the following figure. Analyses may be performed on BW data by the Short Kernel Method in the time domain (similar to filtering in an SE test), or from modal analysis in the frequency response domain (like the Impulse Response method). The BW method was found in the research to be limited to comparatively short pile foundations in soft soil conditions. Source Receiver 1 Receiver 2 Timber Pile Figure 12 Bending waves method
NCHRP 24-25 Page 116 Phase II Appendices Ultraseismic (US) Test The Ultraseismic test (see Figure 13) involves impacting exposed substructure to generate and record the travel of compression or flexural waves down and up substructure at multiple receiver locations on the substructure as shown in the following figure. This test combines the capabilities of the SE/IR and BW measurements with geophysical processing to separate reflections of wave energy coming from foundation elements versus reflections from the top of exposed substructure. The US method was found to be more accurate and applicable than the SE/IR or BW tests. Figure 13 Ultraseismic testing method
NCHRP 24-25 Page 117 Phase II Appendices Spectral Analysis of Surface Waves (SASW) Test The Spectral Analysis of Surface Waves (SASW) test (see Figure 14) involves determining the variation of surface wave velocity vs. depth in layered systems as shown in the following figure. The bottom depths of wall shaped pier and abutment substructures or footings can be determined if they have suitable flat, horizontal and exposed surfaces for testing. The foundation element bottoms are indicated by the slower velocity of surface wave travel in underlying soils. This test was found to be very applicable for these types of foundations where the foundation depths were less than or equal to 2/3 the width of the accessible flat test surface. Figure 14 Spectral analysis of surface waves test Borehole NDE Methods Brief discussions are presented below of the borehole-based Parallel Seismic, Induction Field and Borehole Radar NDE methods for determination of unknown bridge foundation depths.
NCHRP 24-25 Page 118 Phase II Appendices Parallel Seismic (PS) Test The Parallel Seismic (PS) test (see Figure 15) consists of impacting exposed foundation substructure either vertically or horizontally with an impulse hammer to generate compression or flexural waves which travel down the foundation and are transmitted into the surrounding soil as shown in the following figure. The refracted compression (or shear) wave arrival is tracked at regular intervals by a hydrophone receiver suspended in a water-filled cased borehole (original PS procedure) or by a clamped three-component geophone receiver (new procedure-better for shear wave arrivals) in a cased or uncased borehole (if it stands open without caving). The depth of a foundation is typically indicated by a weaker and slower signal arrival below the tip of the foundation. Diffraction of wave energy from the foundation bottom was also found to be indicative of its depth in PS tests as well. The PS test was found to the most accurate and widely applicable NDE method for determination of unknown bridge foundation depths of all tested NDE methods. Suspended hydrophone or clamped 3- component geophone Superstructure Signal Analyzer Figure 15 Parallel seismic method
NCHRP 24-25 Page 119 Phase II Appendices Induction Field (IF) Test The Induction Field (IF) method (see Figure 16) is similar in its application to the Parallel Seismic method, but employs the use of electromagnetic waves instead of stress (sound) waves as shown in the following figure. An electromagnetic field is set up in the ground between a steel pile (or electrically continuous reinforced concrete foundation) and a steel electrode (or other electrically isolated steel containing foundation). A triaxial magnetic field search coil is used to measure the field strength in a PVC cased boring drilled within 1 m (3 ft) or less of the foundation that extends about 3 m (10 ft) below the foundation bottom. When the coil goes below the foundation the field amplitude decreases to a minimum thereby indicating the depth of a steel pile or reinforced foundation. Interpretation of the data from the Induction Field method is complicated by the existence of ferrous or other conductive materials in the bridge structure, and the presence of conductors (such as cables or pipes) in the ground around the pile. The IF test is only applicable to reinforced concrete foundations or steel piles that have accessible, electrically connected rebar/steel. A Choose tapping to maximize current A Return Electrode Pile of interest (s teel) Search Coil PV C cased hole Input Oscillator Detector Transformer Output Figure 16 Induction field method
NCHRP 24-25 Page 120 Phase II Appendices Borehole Radar (BHR) The Ground Penetrating Radar (GPR) method (see Figure 17) as applied in a borehole uses a transmitter/receiver radar antenna to measure the reflection of radar echoes from the side of the bridge substructure foundation as shown in the following figure. The BHR test is most sensitive to foundations of steel or with steel, as the electromagnetic wave energy reflects strongly from steel. The BHR method is limited in its application by wet, conductive clays and salt water as the wave energy is severely attenuated by these subsurface conditions with high dielectric constants. Figure 17 Borehole radar method
NCHRP 24-25 Page 121 Phase II Appendices Crosshole Tomography The Crosshole Tomography (CT) method (see Figure 18) is commonly used to image defects in drilled shafts found by Crosshole Sonic Logging as shown in the following figure. However, where the tubes are inside the concrete shaft tied to the foundation cage for drilled shaft, CT of a bridge substructure involves drilling and typically casing two or more boreholes on opposite sides of an unknown bridge substructure foundation system which are outside of any foundation element. A sonic source is put in at least a borehole and either hydrophone (typically) or geophone (requires grouted casings) receivers are use to sense the arrival times of compressional wave energy for multiple angled ray paths. Straight- to curved-ray analyses are used to produce velocity tomograms and wave amplitude analyses can also be used to attempt to image the unknown foundation elements of a bridge substructure. NSA Engineering of Golden, Colorado has applied the subsurface CT imaging method to identify unknown foundation depths and geometries for piles below pile caps (www.nsaengineering.com). The accuracy and limitation of the CT method are largely unknown at this time and research is needed to further investigate the method. Figure 18 Crosshole tomography method
NCHRP 24-25 Page 122 Phase II Appendices Selection of NDE Methods for Unknown Bridge Foundation Depths The research showed that the borehole-based Parallel Seismic method was both the most accurate and most applicable NDE method for the determination of the depth of unknown bridge foundations for bridge scour safety evaluation purposes. This suggests that it would be valuable to initially perform at least one Parallel Seismic test for each bridge to check the accuracy of depth predictions from any other less costly surface methods that may also be applicable for a given foundation type of the bridge being tested. Ultraseismic or other surface methods that are subsequently proven to be accurate based on a comparison with the Parallel Seismic results may then be used with greater confidence to evaluate unknown foundation depths of other abutments and/or piers on a bridge. It should be noted that as local experience is gained with the use of any of the borehole or surface NDE methods for typical local bridge substructure types and subsurface conditions, the accuracy and applicability of the methods will become much better known to DOT engineers. This local knowledge can then be used to further optimize the selection of NDE methods from technical and cost perspectives. Knowledge of unknown foundation bridge substructure will range from knowing only what is visible to having design drawings and subsurface geology information without as-built plans. Effectiveness of NDE Methods Table 15 shows the ranges of effectiveness of the various methods available for nondestructive evaluation of bridge foundations.
NCHRP 24-25 Page 123 Phase II Appendices Table 15 Effectiveness of NDT Methods Ability to Identify Foundation Parameters Sonic Echo (SE)/Impulse Response (IR) Test (Compressional Echo) Bending Wave (BW) Test (Flexural Echo) Ultraseismic (US) Test (Compressional and Flexural Echo) Spectral Analysis of Surface Wave (SASW) Test Surface Ground Penetrating Radar (GPR) Test Parallel Seismic (PS) Test Borehole Radar (BHR) Test Induction Field (IF) Test Foundation Parameters Depth of Exposed Piles Fair to Good Poor to Good Fair to Excellent Good to Excellent Poor to Excellent None to Excellent Depth of Footing/Cap Poor to Good Poor to Fair Fair to Excellent Fair to Good Poor Good Poor to Good Piles Exist Under Cap? Fair to Poor Good Fair to Good None to Excellent Depth of Pile below Cap? Poor Good to Excellent Fair to Good Geometry of Substructure Fair Poor to Good Poor to Good Fair Fair to Excellent Poor to Fair Material Identification Good Poor to Fair Poor to Fair Poor to Fair Access Requirements Bridge Substructure Yes Yes Yes Yes Yes Yes No Yes Borehole No No No No No Yes Yes Yes Subsurface Complications Low to High Medium to High Low to High Low High Medium High Medium to High Operational Cost $2,000 to $2,500 $2,000 to $2,500 $2,000 to $2,500 $2,000 to $2,500 $2,000 to $2,500 $2,000 to $2,500 $2,000 to $2,500 $2,000 to $2,500 Equipment Cost $10,000 to $20,000 $15,000 to $20,000 $20,000 $20,000 >$30,000 $15,000 to $25,000 >$35,000 $20,000 Required Expertise Field Acquisition Technician Technician Technician Technician- Engineer Technician- Engineer Technician- Engineer Engineer Engineer Data Analysis Engineer Engineer Engineer Engineer Engineer Engineer Engineer Engineer
NCHRP 24-25 Page 124 Phase II Appendices Ability to Identify Foundation Parameters Sonic Echo (SE)/Impulse Response (IR) Test (Compressional Echo) Bending Wave (BW) Test (Flexural Echo) Ultraseismic (US) Test (Compressional and Flexural Echo) Spectral Analysis of Surface Wave (SASW) Test Surface Ground Penetrating Radar (GPR) Test Parallel Seismic (PS) Test Borehole Radar (BHR) Test Induction Field (IF) Test Limitations Most useful for columnar or tabular structures. Response complicated by bridge superstructure elements. Stiff soils and rock limit penetration. Only useful for purely columnar substructure, softer soils, and shorter piles. Response complicated by various bridge superstructur e elements, and stiff soils may show only depth to stiff soil layer. Cannot image piles below cap. Difficult to obtain foundation bottom reflections in stiff soils. Cannot image piles below cap. Use restricted to bridges with flat, longer access for testing. Signal quality is highly controlled by environmental factors. Adjacent substructure reflections complicate data analysis. Higher cost equipment. Difficult to transmit large amount of seismic energy from pile caps to smaller (area) piles. Radar response is highly site dependent (very limited response in conductive, clayey, salt- water saturated soils). It requires the reinforcement in the columns to be electrically connected to the piles underneath the footing. Only applicable to steel or reinforced substructure. Advantages Lower cost equipment and inexpensive testing. Data interpretation for pile foundations may be able to be automated using neural network. Theoretical modeling should be used to plan field tests. Lower cost equipment and inexpensive testing. Theoretical modeling should be used to plan field tests. The horizontal impacts are easy to apply. Lower equipment and testing costs. Can identify the bottom depth of foundation inexpensively for a large class of bridges. Combines compressional and flexural wave reflection tests for complex substructures. Lower equipment and testing costs. Also shows variation of bridge material and subsurface velocities (stiffnesses) vs. depth and thicknesses of accessible elements. Fast testing times. Can indicate geometry of accessible elements and bedrock depths. Lower testing costs. Lower equipment and testing costs. Can detect foundation depths for largest class of bridges and subsurface conditions. Commercial testing equipment is now becoming available for this purpose. Relatively easy to identify reflections from the foundation; however, imaging requires careful processing. Low equipment costs and easy to test. Could work well to complement PS tests and help determine pile type.
NCHRP 24-25 Page 125 Phase II Appendices NDE Conclusions The NCHRP 21-5 and 21-5(2) research resulted in greatly improved understanding of the applicability and accuracy of such NDE methods using sonic, ultrasonic, seismic, magnetic and electromagnetic techniques. Of all of the methods researched, the borehole Parallel Seismic Method was found to be the most accurate and versatile method for determining unknown foundation depths for the broadest range of foundation types. The surface Ultraseismic Method was found to be the most accurate method for determining single substructure element depths such as piles, piers, abutments, etc. However, the Ultraseismic and other surface methods do not provide data on the elements below the first major change in cross-section, such as a pier with a pilecap on piles, where the piles will not be detected. References 1. Olson, L.D., F. Jalinoos, and M.F. Aouad. NCHRP Final Report 21-5: Determination of Unknown Subsurface Bridge Foundations. Federal Highway Administration, Washington D.C., August, 1995. 2. Olson, L.D., and M.F. Aouad. NCHRP Final Report 21-5 (2): Unknown Subsurface Bridge Foundation Testing. Federal Highway Administration, Washington, D.C., June, 2001.
NCHRP 24-25 Page 126 Phase II Appendices APPENDIX F. SCOUR MANAGEMENT CASE STUDIES Table 16 lists the Department of Transportation officials in six States who were invited to participate in a case study of the proposed scour guidelines. These six states were selected for their interest in guidelines for managing bridges with unknown foundations, and for their willingness to complete the survey. Table 16 Case Study Respondents State Name Job Title Survey Completion Time California Steve Ng Chief of structure hydraulics and hydrology 1 month Florida (1/2) Richard Semple Structures management coordinator 2 weeks Florida (1/2) Manuel Luna Assistant structure coordinator 3 weeks New York Robert Burnett Director of geotechnical engineering bureau 2 weeks North Carolina Mohammed Mulla Assistant state geotechnical engineer 1 month Tennessee Wayne Seger Civil engineering manager II 2 weeks Texas Alan Kowalik Bridge inspection branch manager 2 weeks The Initial Bridge Survey The following three pages is a sample of the survey that each official was asked to complete for each one of the ten bridges (over water) they select in their state. In selecting bridges, they were asked to keep the following criteria in mind: Â All the bridges selected should be âover waterâ (i.e. NBI item 113 â âNâ). Â At least half of the bridges selected should have unknown foundations (i.e. NBI item 113 = âUâ). Â Include one bridge that has already failed due to scour if the supporting data for such a case study is available. They were also asked to indicate whether each bridge provides critical access to emergency services (e.g. for a hospital or an evacuation route). Tennessee and Texas responded that they have little or no practical experience with using any field
NCHRP 24-25 Page 127 Phase II Appendices reconnaissance methods, and Tennessee requested the NDE literature review from this report in order to estimate this cost.
NCHRP 24-25 Page 128 Phase II Appendices Bridge #__ Example Page 1 Respondent Information Name E-mail Address Job Title Phone Job Description (In what way does your job involve bridge maintenance?) Mailing Address Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 5 Inventory Route 8 Structure Number 19 Bypass, Detour Length (e.g. in miles) 26 Functional Classification of Inventory Route 27 Year Built 29 Average Daily Traffic 49 Structure Length (e.g. in feet) 52 Deck Width, Out-to-Out (e.g. in feet) 60 Substructure 61 Channel and Channel Protection 71 Waterway Adequacy 109 Average Daily Truck Traffic 113 Scour Critical Bridges (2002 NBI Guidelines)
NCHRP 24-25 Page 129 Phase II Appendices Example Page 2 Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one)  Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $ Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile  Truck running cost $1.30 per mile  Duration of detour * Use Table 2 (days)  Value of time per adult * Use Table 3 ($/hr)  Average car occupancy rate 1.63 people  Value of time for trucks $22.01 per hour  Average detour speed 40 miles per hour  Number of deaths from failure * Use Table 2 (Number of people)  Cost for each life lost $500,000  * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $ Estimated cost of installing scour countermeasures $ Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $ Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $
NCHRP 24-25 Page 130 Phase II Appendices Table 1 Cost of Bridge Construction Example Page 3 Bridge Superstructure Type Total Cost ($/ft2) Reinforced concrete flat slab; simple span $50-65* Reinforced concrete flat slab; continuous span $60-80* Steel deck/girder; simple span $62-75* Steel deck/girder; continuous span $70-90* Pre-stressed concrete deck/girder; simple span $50-70* Pre-stressed concrete deck/girder; continuous span $65-110* Post-tensioned, cast-in-place, concrete box girder cast on scaffolding; span length <=240 ft $75-110 Steel Box Deck/Girder: Span range from 150 ft to 280 ft $76-120 For curvature add a 15 percent premium segmental concrete box girders; span range from 150 ft to 280 ft $80-110 Movable bridges; bascule spans & piers $900-1500 Demolition of existing bridges: Typical $9-15 Bascule spans & piers $63 * Increase the cost by twenty percent for phased construction. Source: http://www.dot.state.fl.us/structures/Manuals/LRFDSDG2002AugChap11.pdf visited on January 12, 2005. Table 2 Bridge Failure Statistics versus Average Daily Traffic Average Daily Traffic (ADT) Cost Multiplier for Early Replacement Detour Duration (days) Number of Lives Lost ADT < 100 1.0 1,095 0 100 < ADT < 500 1.1 730 1 500 < ADT < 1000 1.25 548 2 1000 < ADT < 5000 1.5 365 2 ADT > 5000 2.0 183 5* â 10â * Not an interstate or arterial. â Interstate or arterial. Table 3 Values of Time by State State Value of time ($/hour) State Value of time ($/hour) Alabama $6.29 Montana $5.89 Alaska $8.31 Nebraska $6.51 Arizona $6.88 Nevada $6.76 Arkansas $5.83 New Hampshire $7.38 California $8.27 New Jersey $8.48 Colorado $7.85 New Mexico $6.51 Connecticut $8.75 New York $8.59 Delaware $7.70 North Carolina $6.72 District of Columbia $11.43 North Dakota $6.04 Florida $6.65 Ohio $7.08 Georgia $7.06 Oklahoma $6.14 Guam $5.41 Oregon $7.29 Hawaii $7.24 Pennsylvania $7.09 Idaho $6.46 Puerto Rico $4.35 Illinois $7.61 Rhode Island $7.54 Indiana $6.67 South Carolina $6.29 Iowa $6.31 South Dakota $5.73 Kansas $6.66 Tennessee $6.45 Kentucky $6.34 Texas $6.96 Louisiana $6.16 Utah $6.72 Maine $6.60 Vermont $6.83 Maryland $8.15 Virgin Islands $5.58 Massachusetts $8.93 Virginia $7.71 Michigan $7.80 Washington $8.06 Minnesota $7.85 West Virginia $6.01 Mississippi $5.65 Wisconsin $6.95 Missouri $6.79 Wyoming $6.41 State wage data is from http://www.bls.gov/oes/current/oessrcst.htm, visited on January 12, 2006. This table assumes that the value of time is equal to 41% of the mean hourly wage, as proposed by José A. Gómez-Ibáñez, William B. Tye, Clifford Winston, âEssays in Transportation Economics and Policy: A Handbook in Honor of John R. Meyerâ, 1999.
NCHRP 24-25 Page 131 Phase II Appendices Case Study Evaluations and Responses After each state completed and returned the surveys, the âScour Risk Management Guidelinesâ were applied to each case study. Then a one to two-page summary was written to explain how the guidelines selected a pertinent management plan. Note that each state also received a copy of three tables for calculating probability of failure and directions for creating a bridge closure plan (i.e. Tables 14â16 and âDevelop a Bridge Closure Planâ from the main report). These summaries were returned to the survey respondents, who were then asked to comment on the recommendations. Each survey respondent was specifically asked to use the following questions to guide their comments: Â Do you agree with the final recommendation for each of the bridges with unknown foundations? Please explain with specific examples. Â Given the analysis that we have presented, do you have suggestions for improving the predicted vulnerability ratings? Please explain with specific examples. Â Do you have any concerns about using risk to select a management plan when a bridge foundation is truly unknown? Â Are there any other factors that might influence your risk management decisions? All of the survey correspondence is presented in the next five subsections, which are organized by state, and then by case study. Each case study heading has the completed survey form and the management plan obtained from the âScour Risk Management Guidelinesâ. All of the comments about the management summaries are presented after each Stateâs set of case studies because many of the comments apply to the general approach or to a comparison of case studies.
NCHRP 24-25 Page 132 Phase II Appendices California Bridges Bridge #1 The Initial Survey Respondent Information Name Luis Avila E-mail Address Luis_Avila@dot.ca.gov Job Title Transportation Engineer Phone (916) 227-8030 Job Description (In what way does your job involve bridge maintenance?) Substructure inspection for Bridges over water. Mailing Address 1801 30th St. Sacramento, CA 95816 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. North Arm Newport Bay, Bridge Number 55-0621M, District 12, Route 00001, Post Mile 18.38 A continuous two spans RC slab bridge on a single column RC bent and open-end RC diaphragm abutments, all are on driven RC piles. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 069 5 Inventory Route 00001 8 Structure Number 55 0621M 19 Bypass, Detour Length (e.g. in miles) No entry (1.9 mi)* 26 Functional Classification of Inventory Route No entry (14)* 27 Year Built 1982 29 Average Daily Traffic No entry (59,000)* 49 Structure Length (e.g. in feet) 113.84 ft 52 Deck Width, Out-to-Out (e.g. in feet) No entry (11.6 ft)* 60 Substructure 7 - Good 61 Channel and Channel Protection 8 - Protected 71 Waterway Adequacy 8 â Equal Desirable 109 Average Daily Truck Traffic No entry (0)* 113 Scour Critical Bridges (2002 NBI Guidelines) U â Undefined Code *This bridge has missing NBI data which was estimated using structure number â55 0614â since this bridge supports the same route over the same water body.
NCHRP 24-25 Page 133 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) x Simple Span(s) Â Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 51 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $200,000 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile x Truck running cost $1.30 per mile x Duration of detour * Use Table 2 (days) x 183 Value of time per adult * Use Table 3 ($/hr) x $8.27 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 10 Cost for each life lost $500,000 x * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $25,000 Estimated cost of installing scour countermeasures $30,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000
NCHRP 24-25 Page 134 Phase II Appendices Scour Management Evaluation 1. Route 1 over the North Arm of Newport Bay Bridge 55-0614 in Newport Beach, CA was constructed in 1982 and supports an urban principal arterial class road. This bridge has an unknown foundation depth and is not recorded in the NBI. It is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports an urban principal arterial, which provides access to emergency services and has significant economic value. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge probably provides critical access to local services and has significant economic value. Thus, because this bridge has an unknown foundation the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 135 Phase II Appendices Bridge #2 The Initial Survey Respondent Information Name Luis Avila E-mail Address Luis_Avila@dot.ca.gov Job Title Transportation Engineer Phone (916) 227-8030 Job Description (In what way does your job involve bridge maintenance?) Substructure inspection for Bridges over water. Mailing Address 1801 30th St. Sacramento, CA 95816 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. San Luis Rey River, Bridge Number 57-0043Z, District 11, Route 00076, Post Mile 9.58 Parabolic RC girders (2) at end spans and RC arch spans with RC diaphragm abutments and RC piers (2 legs) all founded on spread footings except pier 5 and 6 are on timber piles National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 069 5 Inventory Route 00076 8 Structure Number 57 0043Z 19 Bypass, Detour Length (e.g. in miles) No entry (50 mi)* 26 Functional Classification of Inventory Route No entry (06)* 27 Year Built 1925 29 Average Daily Traffic No entry (3,600)* 49 Structure Length (e.g. in feet) 671.91 ft 52 Deck Width, Out-to-Out (e.g. in feet) 23.95 ft 60 Substructure No entry (6)* 61 Channel and Channel Protection 7 â Minor Damage 71 Waterway Adequacy 7 â Above Minimum 109 Average Daily Truck Traffic No entry (1%)* 113 Scour Critical Bridges (2002 NBI Guidelines) U â Undefined Code *This bridge has missing NBI data which was estimated using structure number â57 0171â since this bridge supports the same route over the same water body.
NCHRP 24-25 Page 136 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge, which in not documented in the NBI database. Description User Input Bridge Type (check only one) xSimple Span(s) x Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 10 Years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $2,800,000 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile x Truck running cost $1.30 per mile x Duration of detour * Use Table 2 (days) x 365 Value of time per adult * Use Table 3 ($/hr) x $8.27 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 2 Cost for each life lost $500,000 x * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $45,000 Estimated cost of installing scour countermeasures $2,800,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000
NCHRP 24-25 Page 137 Phase II Appendices Scour Management Evaluation 2. State Route 76 over San Luis Rey River Bridge 57-0043Z in San Diego County, CA was constructed in 1925 and supports a rural minor arterial class road. This bridge has an unknown foundation depth and is not recorded in the NBI. It is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency evacuation route, and does not provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor arterial class bridge, according to the Guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (12/2005 NBI database) 6* Rural minor arterial classification NBI item 71 (bridge survey) 7 Waterway exceeds the minimum criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (12/2005 NBI database) 6* Foundation is in satisfactory condition NBI item 61 (bridge survey) 7 Channel has some minor drift and damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year *Missing NBI values were selected based on a parallel bridge (NBI item 8 = â57-0171â). This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (10 years, according to the survey respondent) as follows:1-(1-0.00025)10, or about 0.0025 (a 1 in 400 chance of failure in the next 10 years). This and other survey data are now used to calculate the risk of death as follows: 497,2$)2()/000,500($)/0025.0()67.0( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $45,000 and the risk of death is $2,497, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 138 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $2,800,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $2,800,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data (partly from bridge #57-0171) as follows: 450,123,30$ )365()/3600()50( 100 1/30.1$ 100 11/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 168,281,22$ /40 )365()/3600()50( 100 1)/01.22($ 100 11)63.1()/27.8($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $56,204,618. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of 0.67, the lifetime probability of failure, and the total cost of failure â about $94,037. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures (assuming that scour countermeasures really costs the same as a new bridge). However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 139 Phase II Appendices Bridge #3 The Initial Survey Respondent Information Name Luis Avila E-mail Address Luis_Avila@dot.ca.gov Job Title Transportation Engineer Phone (916) 227-8030 Job Description (In what way does your job involve bridge maintenance?) Substructure inspection for Bridges over water. Mailing Address 1801 30th St. Sacramento, CA 95816 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. San Felipe Creek, Bridge Number 57-0096, District 11, Route 00078, Post Mile 72.92 Continuous 5 span RC haunched T-girders (3) with cantilever end spans on 2 column bents on spread footings. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 069 5 Inventory Route 00078 8 Structure Number 57 0096 19 Bypass, Detour Length (e.g. in miles) 19.88 mile 26 Functional Classification of Inventory Route 06-Rural Minor Arterial 27 Year Built 1948 29 Average Daily Traffic 1150 49 Structure Length (e.g. in feet) 165.03 ft 52 Deck Width, Out-to-Out (e.g. in feet) 28.54 ft 60 Substructure 7 - Good 61 Channel and Channel Protection 8 - Protected 71 Waterway Adequacy 8 â Equal Desirable 109 Average Daily Truck Traffic 1 113 Scour Critical Bridges (2002 NBI Guidelines) U â Undefined Code
NCHRP 24-25 Page 140 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) x Simple Span(s) Â Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 18 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $900,000 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile x Truck running cost $1.30 per mile x Duration of detour * Use Table 2 (days) x 365 Value of time per adult * Use Table 3 ($/hr) x $8.27 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 2 Cost for each life lost $500,000 x * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $25,000 Estimated cost of installing scour countermeasures $100,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000
NCHRP 24-25 Page 141 Phase II Appendices Scour Management Evaluation 3. State Route 78 over San Felipe Creek Bridge 57-0096 in San Diego County, CA was constructed in 1948 and supports a rural minor arterial class road. This bridge has an unknown foundation depth and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency evacuation route, and does not provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor arterial class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 6 Rural minor arterial classification NBI item 71 (bridge survey) 8 Waterway meets the desirable criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 7 Foundation is in good condition NBI item 61 (bridge survey) 8 Channel is stable and protected by vegetation â´Scour Vulnerability (guidelines) 7 Countermeasures were installed and is now stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (18 years, according to the survey respondent) as follows:1-(1-0.00025)18, or about 0.0045 (a 1 in 222 chance of failure in the next 18 years). This and other survey data are now used to calculate the risk of death as follows: 490,4$)2()/000,500($)/0025.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $25,000 and the risk of death is $4,490, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 142 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $100,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $900,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 862,829,3$ )365()/150,1()20( 100 1/30.1$ 100 11/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 803,832,2$ /40 )365()/150,1()20( 100 1)/01.22($ 100 11)63.1()/27.8($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $8,562,665. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $38,450. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures. However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 143 Phase II Appendices Bridge #4 The Initial Survey Respondent Information Name Luis Avila E-mail Address Luis_Avila@dot.ca.gov Job Title Transportation Engineer Phone (916) 227-8030 Job Description (In what way does your job involve bridge maintenance?) Substructure inspection for Bridges over water. Mailing Address 1801 30th St. Sacramento, CA 95816 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. North Fork Kings River, Bridge Number 45-0019R, District 06, Route 00041, Post Mile R47.16 Original: 7 span, continuous RC girder. Widening: 9 span, continuous RC slab. Present bridge on RC pile (8) bents and closed end cantilever abutments. All founded on concrete piles. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 069 5 Inventory Route 00041 8 Structure Number 45 0019R 19 Bypass, Detour Length (e.g. in miles) 1.24 mile 26 Functional Classification of Inventory Route 02-Rural Other Princ 27 Year Built 1959-reconstructed, built ? 29 Average Daily Traffic 7800 49 Structure Length (e.g. in feet) 24.21 ft 52 Deck Width, Out-to-Out (e.g. in feet) 42.65 ft 60 Substructure 6-Satisfactory 61 Channel and Channel Protection 5-Bank Protection Eroded 71 Waterway Adequacy 8 â Equal Minimum 109 Average Daily Truck Traffic 14 113 Scour Critical Bridges (2002 NBI Guidelines) U â Undefined Code
NCHRP 24-25 Page 144 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) x Simple Span(s) Â Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 10 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $1,800,000 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile x Truck running cost $1.30 per mile x Duration of detour * Use Table 2 (days) x 183 Value of time per adult * Use Table 3 ($/hr) x $8.27 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 10 Cost for each life lost $500,000 x * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $30,000 Estimated cost of installing scour countermeasures $1,800,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000
NCHRP 24-25 Page 145 Phase II Appendices Scour Management Evaluation 4. State Route 41 NB over the North Fork of Kings River Bridge 45-0019R in Kings County, CA was constructed in 1959 and reconstructed in 2000 and supports a rural principal arterial class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural principal arterial, which has significant economic value and may provide access to critical local services. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has significant economic value and may provide critical access to local services. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 146 Phase II Appendices Bridge #5 The Initial Survey Respondent Information Name Luis Avila E-mail Address Luis_Avila@dot.ca.gov Job Title Transportation Engineer Phone (916) 227-8030 Job Description (In what way does your job involve bridge maintenance?) Substructure inspection for Bridges over water. Mailing Address 1801 30th St. Sacramento, CA 95816 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Kings River, Bridge Number 45-0063, District 06, Route 00043, Post Mile 26.4 Continuous RC slab on pile (6) bents and open-end pile cap abutments. All founded on concrete piles. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 069 5 Inventory Route 00043 8 Structure Number 45 0063 19 Bypass, Detour Length (e.g. in miles) 13.05 mile 26 Functional Classification of Inventory Route 06-Rural Minor Arterial 27 Year Built 1954 29 Average Daily Traffic 8410 49 Structure Length (e.g. in feet) 23.49 ft 52 Deck Width, Out-to-Out (e.g. in feet) 8.26 ft 60 Substructure 7 - Good 61 Channel and Channel Protection 6-Bank Slumping 71 Waterway Adequacy 8 â Equal Desirable 109 Average Daily Truck Traffic 15 113 Scour Critical Bridges (2002 NBI Guidelines) U â Undefined Code
NCHRP 24-25 Page 147 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) x Simple Span(s) Â Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 23 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $1,000,000 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile x Truck running cost $1.30 per mile x Duration of detour * Use Table 2 (days) x 183 Value of time per adult * Use Table 3 ($/hr) x $8.27 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 10 Cost for each life lost $500,000 x * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $25,000 Estimated cost of installing scour countermeasures $100,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000
NCHRP 24-25 Page 148 Phase II Appendices Scour Management Evaluation 5. State Route 43 over Kings River Bridge 45-0063 in Kings County, CA was constructed in 1954 and reconstructed in 1985 and supports a rural minor arterial class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor arterial class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 6 Rural minor arterial classification NBI item 71 (bridge survey) 8 Waterway meets the desirable criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 7 Foundation is in good condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (23 years, according to the survey respondent) as follows:1-(1-0.00025)23, or about 0.0057 (a 1 in 175 chance of failure in the next 23 years). This and other survey data are now used to calculate the risk of death as follows: 671,28$)10()/000,500($)0057.0()0.1( 6 =â â â = â â â = peopleperson XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $25,000 and the risk of death is $28,671, automated scour monitoring may be warranted. However, before installing automated scour monitoring, we should determine if scour countermeasures are also warranted.
NCHRP 24-25 Page 149 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $100,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $1,000,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 268,554,11$ )183()/410,8()13( 100 15/30.1$ 100 151/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 519,382,7$ /40 )183()/410,8()13( 100 15)/01.22($ 100 151)63.1()/27.8($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $23,936,771. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $114,332. Thus, scour countermeasures are probably warranted because the lifetime risk of failure is greater than the estimated cost of scour countermeasures. The guidelines further recommend that you install countermeasures rather than automated scour monitoring. Is foundation reconnaissance and scour analysis warranted? The survey respondent estimated the foundation reconnaissance and scour analysis costs to be about $20,000 and $5,000, respectively. Since this is only about 25% of the estimated cost of installing countermeasures, foundation reconnaissance and scour analysis are probably warranted before installing the countermeasures. Recommended management strategy Given the results explained above, the guidelines recommend the following steps to ensure the safety of the bridge: 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, you could drill through the footing to determine elevation of the footing bottom. The parallel seismic test is generally the most effective NDT method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth using local knowledge. This should be a conservative assumption. Spread footing depths are
NCHRP 24-25 Page 150 Phase II Appendices easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 151 Phase II Appendices Bridge #6 The Initial Survey Respondent Information Name Luis Avila E-mail Address Luis_Avila@dot.ca.gov Job Title Transportation Engineer Phone (916) 227-8030 Job Description (In what way does your job involve bridge maintenance?) Substructure inspection for Bridges over water. Mailing Address 1801 30th St. Sacramento, CA 95816 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. San Juan Creek, Bridge Number 55-0228, District 12, Route 00005, Post Mile 8.87 A simply supported 4 span composite welded steel girder (15 each) with RC open end cantilever abutments and solid pier walls, all supported on concrete driven piles. High Priority structure. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 069 5 Inventory Route 00005 8 Structure Number 55 0228 19 Bypass, Detour Length (e.g. in miles) 1.24 mile 26 Functional Classification of Inventory Route 11-Urban Interstate 27 Year Built 1958 29 Average Daily Traffic 212000 49 Structure Length (e.g. in feet) 609.91 ft 52 Deck Width, Out-to-Out (e.g. in feet) 160.10 ft 60 Substructure 5-Fair 61 Channel and Channel Protection 5-Bank Protection Eroded 71 Waterway Adequacy 8 â Equal Desirable 109 Average Daily Truck Traffic 0 113 Scour Critical Bridges (2002 NBI Guidelines) 3-3 SC - Unstable
NCHRP 24-25 Page 152 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) x Simple Span(s) Â Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 27 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $17,000,000 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile x Truck running cost $1.30 per mile x Duration of detour * Use Table 2 (days) x 183 Value of time per adult * Use Table 3 ($/hr) x $8.27 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 10 Cost for each life lost $500,000 x * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $45,000 Estimated cost of installing scour countermeasures $200,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000
NCHRP 24-25 Page 153 Phase II Appendices Scour Management Evaluation 6. Interstate 5 over San Juan Creek Bridge 55-0228 in San Clemente, CA was constructed in 1958 and reconstructed in 1996 and supports an urban interstate. This bridgeâs foundation is known with an NBI item 113 rating of â3â (scour critical and unstable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports an urban interstate, which is emergency evacuation route, and provides direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has a known foundation, and requires action. This bridge furthermore provides critical access to local services and has significant economic value. Thus, if this bridge had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 154 Phase II Appendices Bridge #7 The Initial Survey Respondent Information Name Luis Avila E-mail Address Luis_Avila@dot.ca.gov Job Title Transportation Engineer Phone (916) 227-8030 Job Description (In what way does your job involve bridge maintenance?) Substructure inspection for Bridges over water. Mailing Address 1801 30th St. Sacramento, CA 95816 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Pala Creek, Bridge Number 57-0072, District 11, Route 00076, Post Mile 23.23 Continuous seven span with cantilever ends RC haunched slab with RC open-end diaphragm abutments and five column bents, all founded on concrete piles. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 069 5 Inventory Route 00076 8 Structure Number 57 0072 19 Bypass, Detour Length (e.g. in miles) 1.24 mile 26 Functional Classification of Inventory Route 06-Rural Minor Arterial 27 Year Built 1938 29 Average Daily Traffic 123000 49 Structure Length (e.g. in feet) 122.05 ft 52 Deck Width, Out-to-Out (e.g. in feet) 33.14 ft 60 Substructure 5-Fair 61 Channel and Channel Protection 3-Bank Protection Eroded 71 Waterway Adequacy 8 â Equal Desirable 109 Average Daily Truck Traffic 16 113 Scour Critical Bridges (2002 NBI Guidelines) 3-3 SC - Unstable
NCHRP 24-25 Page 155 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) x Simple Span(s) Â Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 10 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $700,000 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile x Truck running cost $1.30 per mile x Duration of detour * Use Table 2 (days) x 183 Value of time per adult * Use Table 3 ($/hr) x $8.27 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 10 Cost for each life lost $500,000 x * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $25,000 Estimated cost of installing scour countermeasures $700,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000
NCHRP 24-25 Page 156 Phase II Appendices Scour Management Evaluation 7. State Route 76 over Pala Creek Bridge 57-0072 in San Diego County, CA was constructed in 1938 and supports a rural minor arterial class road. This bridgeâs foundation is known with an NBI item 113 rating of â3â (scour critical and unstable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor arterial class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 6 Rural minor arterial classification NBI item 71 (bridge survey) 8 Waterway meets the desirable criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 5 Foundation is in fair condition NBI item 61 (bridge survey) 3 Bank protection has failed and threatens the bridge â´Scour Vulnerability (guidelines) 4 Analysis: stable; Survey: foundation is exposed â´Annual probability of failure (guidelines) 0.0005 A 1 in 2,000 chance of failure in any given year This bridge does not meet the minimum performance level because the annual probability of failure is not less than 0.0005. Recommended management strategy This bridge has a known foundation, and requires action. Furthermore, this bridge does not meet the minimum performance level for bridges with unknown foundations. Thus, if this bridge had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known.
NCHRP 24-25 Page 157 Phase II Appendices 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 158 Phase II Appendices Bridge #8 The Initial Survey Respondent Information Name Luis Avila E-mail Address Luis_Avila@dot.ca.gov Job Title Transportation Engineer Phone (916) 227-8030 Job Description (In what way does your job involve bridge maintenance?) Substructure inspection for Bridges over water. Mailing Address 1801 30th St. Sacramento, CA 95816 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Cottonwood Creek, Bridge Number 41-0025, District 06, Route 00145, Post Mile 5.39 Continuous RC slab pile (3) bents and wall abutments. All founded on concrete piles. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 069 5 Inventory Route 00145 8 Structure Number 41 0025 19 Bypass, Detour Length (e.g. in miles) 21.75 mile 26 Functional Classification of Inventory Route 14-Urban Other Princ 27 Year Built 1953 29 Average Daily Traffic 21600 49 Structure Length (e.g. in feet) 131.89 m 52 Deck Width, Out-to-Out (e.g. in feet) 32.15 m 60 Substructure No entry (7)* 61 Channel and Channel Protection 5-Bank Protection Eroded 71 Waterway Adequacy 7-Above Minimum 109 Average Daily Truck Traffic 7 113 Scour Critical Bridges (2002 NBI Guidelines) 3-3 SC - Unstable *This missing data was filled in based on NBI item 67 = â7â.
NCHRP 24-25 Page 159 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) x Simple Span(s) Â Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 22 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $800,000 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile x Truck running cost $1.30 per mile x Duration of detour * Use Table 2 (days) x 183 Value of time per adult * Use Table 3 ($/hr) x $8.27 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 10 Cost for each life lost $500,000 x * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $25,000 Estimated cost of installing scour countermeasures $200,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000
NCHRP 24-25 Page 160 Phase II Appendices Scour Management Evaluation 8. State Route 145 over Cottonwood Creek Bridge 41-0025 in Medera County, CA was constructed in 1953 and supports an urban principal arterial class road. This bridgeâs foundation is known with an NBI item 113 rating of â3â (scour critical and unstable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports an urban principal arterial, which has significant economical value and may provide critical access to local services. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has a known foundation, and requires action. Furthermore, this bridge has significant economic value and may provide critical access to local services. Thus, if this bridge had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 161 Phase II Appendices Bridge #9 The Initial Survey Respondent Information Name Luis Avila E-mail Address Luis_Avila@dot.ca.gov Job Title Transportation Engineer Phone (916) 227-8030 Job Description (In what way does your job involve bridge maintenance?) Substructure inspection for Bridges over water. Mailing Address 1801 30th St. Sacramento, CA 95816 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Russian River, Bridge Number 20-0038, District 04, Route 00128, Post Mile 5.44 21 spans with 6 riveted steel pony truss spans on RC columns with curtain wall piers with 4 western approach T beam spans on RC column bents and 11 eastern approach T beam spans on RC column bents and angle wing abutments. All founded on timber piles of unknown depth and soil type. (Bridge failed 12/24/2005, presumably due to scour.) National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 069 5 Inventory Route 00128 8 Structure Number 20 0038 19 Bypass, Detour Length (e.g. in miles) 13.05 mile 26 Functional Classification of Inventory Route 06-Rural Minor Arterial 27 Year Built 1932 29 Average Daily Traffic 2400 49 Structure Length (e.g. in feet) 975.06 ft 52 Deck Width, Out-to-Out (e.g. in feet) 32.15 ft 60 Substructure 4-Poor 61 Channel and Channel Protection 1-Br Closed-Correct (7)* 71 Waterway Adequacy 8 â Equal Desirable (8)* 109 Average Daily Truck Traffic 12 113 Scour Critical Bridges (2002 NBI Guidelines) 0-0 SC â Bridge Failed (U)* *This bridge failed on 12/24/2005, and the codes in parentheses were recorded a month before a new survey revealed that failure was immanent.
NCHRP 24-25 Page 162 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) x Simple Span(s) x Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed Failed at 74 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $30,000,000 (Emergency Replacement) Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile x Truck running cost $1.30 per mile x Duration of detour * Use Table 2 (days) x 365 Value of time per adult * Use Table 3 ($/hr) x $8.27 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 2 Cost for each life lost $500,000 x * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $45,000 Estimated cost of installing scour countermeasures $30,000,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000
NCHRP 24-25 Page 163 Phase II Appendices Scour Management Evaluation 9. State Route 128 over Russian River Bridge 20-0038 in Sonoma County, CA was constructed in 1932 and reconstructed in 1972 and supports a rural minor arterial road. This bridge failed on December 24, 2005, but it had an unknown foundation depth before it failed. The NBI codes before it failed were recovered from the 2005 NBI database, and this data will be used to test the scour guidelines. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor arterial class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 6 Rural minor arterial classification NBI item 71 (bridge survey) 8 Waterway meets the desirable criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 4 Foundation is in poor condition NBI item 61 (12/2005 NBI database) 8 Channel is stable and protected by vegetation â´Scour Vulnerability (guidelines) 4 Analysis: stable; Survey: foundation is exposed â´Annual probability of failure (guidelines) 0.0005 A 1 in 2,000 chance of failure in any given year This bridge does not meet the minimum performance level because the annual probability of failure is not less than 0.0005. Recommended management strategy This bridge does not meet the minimum performance level. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual.
NCHRP 24-25 Page 164 Phase II Appendices 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 165 Phase II Appendices Bridge #10 The Initial Survey Respondent Information Name Luis Avila E-mail Address Luis_Avila@dot.ca.gov Job Title Transportation Engineer Phone (916) 227-8030 Job Description (In what way does your job involve bridge maintenance?) Substructure inspection for Bridges over water. Mailing Address 1801 30th St. Sacramento, CA 95816 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Clear Creek, Bridge Number 12-0073, District 03, Route 00149, Post Mile 3.72 Continuous RC slab with RC 5-column bents and RC closed end backfilled strutted abutments all on spread footings. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 069 5 Inventory Route 00149 8 Structure Number 12 0073 19 Bypass, Detour Length (e.g. in miles) 8.7 mile 26 Functional Classification of Inventory Route 02-Rural Other Princ 27 Year Built 1951 29 Average Daily Traffic 12900 49 Structure Length (e.g. in feet) 73.16 ft 52 Deck Width, Out-to-Out (e.g. in feet) 43.64 ft 60 Substructure 6-Satisfactory 61 Channel and Channel Protection 7-Minor Damage 71 Waterway Adequacy 8 â Equal Desirable 109 Average Daily Truck Traffic 7 113 Scour Critical Bridges (2002 NBI Guidelines) 2-2 SC â Extensive Scour
NCHRP 24-25 Page 166 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) x Simple Span(s) Â Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 20 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $600,000 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile x Truck running cost $1.30 per mile x Duration of detour * Use Table 2 (days) x 183 Value of time per adult * Use Table 3 ($/hr) x $8.27 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 10 Cost for each life lost $500,000 x * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $25,000 Estimated cost of installing scour countermeasures $100,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000
NCHRP 24-25 Page 167 Phase II Appendices Scour Management Evaluation 10. State Route 149 over Clear Creek Bridge 12-0073 in Butte County, CA was constructed in 1951 and reconstructed in 1975 and supports a rural principal arterial class road. This bridgeâs foundation is known with an NBI item 113 rating of â2â (Analysis: scour critical; Survey: immediate action recommended). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural principal arterial, which has significant economical value and may provide critical access to local services. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has a known foundation, and requires action. Furthermore, this bridge has significant economic value and may provide critical access to local services. Thus, if this bridge had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 168 Phase II Appendices Response to Evaluations Steve Ng inserted comments into the management summary document, for convenience. His first comment appears in the second paragraph of the âDevelop a Bridge Closure Planâ section of the summary. He said, âConsider installing a remote stage sensor in lieu of just paint on the substructure. These sensors are fairly simple, reliable instruments. They can be set for numerous trigger elevations to tailor to the site needs and would not require the physical presence of personnel until conditions warrantâ. At the end of the management summaries Mr. Ng added the following comments. General Comments: I noticed that if information is missing regarding detour miles and duration or ADT, default information was assumed. I would consider setting the defaults higher with notation regarding the conservative value (or do you have defaults tied to Route importance?) This will increase costs and put more pressure to obtain real or at least more representative information. Making recommendations for additional borings is fine, but there are costs, time, permits and environmental concerns. [What about] NDT costs and reliability? Do you have any guidance? Unknown pile lengths: you assume they are 10 feet and move on. Sometimes the predicted scour will be below that 10 foot [assumption]. Geology will play a role. Also what happens if you do say that the scour is okay under this condition and the soils are not scour [prone]. Donât lead the evaluation to a âno work recommendedâ condition if there is no other consideration for seismic events. I was hoping to see some guidance regarding when it is appropriate to just rock and monitor without additional investigations or in lieu of a big effort to fine line evaluate all factors.
NCHRP 24-25 Page 169 Phase II Appendices Florida Bridges Bridge #1 The Initial Survey Respondent Information Name Richard C. Semple E-mail Address Richard.semple@dot.state.fl.us Job Title Structures Management Coordinator Phone 813-744-6050 Job Description (In what way does your job involve bridge maintenance?) Bridge Inspection Repair Plans Production Scour Evaluation Oversight Mailing Address District Structures & Facilities District 1 & 7 2916 Leslie Road Tampa, FL 35619 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. BR #030145 US 41 NE over Fahka Union Canal Location: 13.7 miles SE of ST 951 MP: 39.214 Emergency Route National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 12 5 Inventory Route 1 8 Structure Number 030145 19 Bypass, Detour Length (e.g. in miles) 0.6 mi 26 Functional Classification of Inventory Route 02 27 Year Built 1969 29 Average Daily Traffic 2100 49 Structure Length (e.g. in feet) 219.2 ft 52 Deck Width, Out-to-Out (e.g. in feet) 420 ft 60 Substructure 7 61 Channel and Channel Protection 8 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 11% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 170 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 13years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 9206 ft2; Cost per unit area: 70 $/ft2; Cost Multiplier: 1.5 $96,630.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠365 Value of time per adult * Use Table 3 ($/hr) ⧠$6.65 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $7,000.00/unit Estimated cost of installing scour countermeasures $35,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $6,015.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $10,808.00
NCHRP 24-25 Page 171 Phase II Appendices Scour Management Evaluation 1. US Highway 41 over Fahka Union Canal Bridge 030146 in Collier County, FL was constructed in 1969. It supports a rural principal arterial. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural principal arterial road, which is also an emergency evacuation route. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge provides a critical emergency route for local residents and has significant economic value. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 172 Phase II Appendices Bridge #2 The Initial Survey Respondent Information Name Richard C. Semple E-mail Address Richard.semple@dot.state.fl.us Job Title Structures Management Coordinator Phone 813-744-6050 Job Description (In what way does your job involve bridge maintenance?) Bridge Inspection Repair Plans Production Scour Evaluation Oversight Mailing Address District Structures & Facilities District 1 & 7 2916 Leslie Road Tampa, FL 35619 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. BR# 050018. ST 78 over Indian Prairie Canal Location: 7.4 miles E of CR 721 MP: 20.665 Emergency Route National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 12 5 Inventory Route 1 8 Structure Number 050018 19 Bypass, Detour Length (e.g. in miles) 34.8 mi 26 Functional Classification of Inventory Route 06 27 Year Built 1960 29 Average Daily Traffic 3,200 49 Structure Length (e.g. in feet) 225 ft 52 Deck Width, Out-to-Out (e.g. in feet) 33.8 ft 60 Substructure 7 61 Channel and Channel Protection 9 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 18% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 173 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 4 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 7605 ft2; Cost per unit area: 70 $/ft2; Cost Multiplier: 1.5 $798,525.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠365 Value of time per adult * Use Table 3 ($/hr) ⧠$6.65 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $7,000.00/unity Estimated cost of installing scour countermeasures $35,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $6,015.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $10,808.00
NCHRP 24-25 Page 174 Phase II Appendices Scour Management Evaluation 2. State Route 78 over Indian Prairie Canal Bridge 050018 in Glades County, FL was constructed in 1960 and supports a rural minor arterial class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is an emergency evacuation route. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge provides a critical emergency route for local residents and has significant economic value. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 175 Phase II Appendices Bridge #3 The Initial Survey Respondent Information Name Richard C. Semple E-mail Address Richard.semple@dot.state.fl.us Job Title Structures Management Coordinator Phone 813-744-6050 Job Description (In what way does your job involve bridge maintenance?) Bridge Inspection Repair Plans Production Scour Evaluation Oversight Mailing Address District Structures & Facilities District 1 & 7 2916 Leslie Road Tampa, FL 35619 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. BR# 120160. SR 80 over Orange River Location: 0.4 miles E of I-75 M.P.: 0.026 Emergency Route National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 12 5 Inventory Route 1 8 Structure Number 120160 19 Bypass, Detour Length (e.g. in miles) 6.2 26 Functional Classification of Inventory Route 14 27 Year Built 1990 29 Average Daily Traffic 27,500 49 Structure Length (e.g. in feet) 800 ft 52 Deck Width, Out-to-Out (e.g. in feet) 123 ft 60 Substructure 7 61 Channel and Channel Protection 8 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 13% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 176 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 34 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 98,468 ft2; Cost per unit area: 70 $/ft2; Cost Multiplier: 2.0 $13,777,120.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠183 Value of time per adult * Use Table 3 ($/hr) ⧠$6.65 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠10 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $7,000/unit Estimated cost of installing scour countermeasures $35,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $6,015.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $10,808.00
NCHRP 24-25 Page 177 Phase II Appendices Scour Management Evaluation 3. State Route 80 over Orange River Bridge 120160 in Fort Myers, FL was constructed in 1990 and supports an urban principal arterial road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports an urban principal arterial road, which is also an emergency evacuation route. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge provides a critical emergency route for local residents and has significant economic value. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 178 Phase II Appendices Bridge #4 The Initial Survey Respondent Information Name Richard C. Semple E-mail Address Richard.semple@dot.state.fl.us Job Title Structures Management Coordinator Phone 813-744-6050 Job Description (In what way does your job involve bridge maintenance?) Bridge Inspection Repair Plans Production Scour Evaluation Oversight Mailing Address District Structures & Facilities District 1 & 7 2916 Leslie Road Tampa, FL 35619 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. BR# 120165 ST 80 EB over Bediman Creek Location: 0.1 miles E of CR 884 MP: 18.333 Emergency route National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 12 5 Inventory Route 1 8 Structure Number 120165 19 Bypass, Detour Length (e.g. in miles) 0.6 mi 26 Functional Classification of Inventory Route 02 27 Year Built 2006 29 Average Daily Traffic 5841 49 Structure Length (e.g. in feet) 120.1 ft 52 Deck Width, Out-to-Out (e.g. in feet) 45.1 ft 60 Substructure 8 61 Channel and Channel Protection 8 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 13% 113 Scour Critical Bridges (2002 NBI Guidelines) 8
NCHRP 24-25 Page 179 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one)  Simple Span(s) ⧠Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 50 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 5172 ft2; Cost per unit area 80 $/ft2; Cost Multiplier: 2.0 $827,520.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠183 Value of time per adult * Use Table 3 ($/hr) ⧠$6.65 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠10 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $7,000/unit Estimated cost of installing scour countermeasures $35,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $6,015.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $10,808.00
NCHRP 24-25 Page 180 Phase II Appendices Scour Management Evaluation 4. State Route 80 EB over Bedman Creek Bridge 120165 in Lee County, FL was constructed in 2006 and supports a rural principal arterial class road. This bridgeâs foundation is known with an NBI item 113 rating of â8â (Analysis: stable; Survey: stable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural principal arterial, which is also an emergency evacuation route. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. This bridge is an evacuation route and has significant economic value. Thus, if this bridge had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 181 Phase II Appendices Bridge #5 The Initial Survey Respondent Information Name Richard C. Semple E-mail Address Richard.semple@dot.state.fl.us Job Title Structures Management Coordinator Phone 813-744-6050 Job Description (In what way does your job involve bridge maintenance?) Bridge Inspection Repair Plans Production Scour Evaluation Oversight Mailing Address District Structures & Facilities District 1 & 7 2916 Leslie Road Tampa, FL 35619 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. BR#160063. SR 37 over N. Fork Alafia River Location: 0.4 miles S of ST 60 MP: 17.787 Not Emergency National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 12 5 Inventory Route 1 8 Structure Number 16006.3 19 Bypass, Detour Length (e.g. in miles) 6.2 mi 26 Functional Classification of Inventory Route 1.6 27 Year Built 1957 29 Average Daily Traffic 11,500 49 Structure Length (e.g. in feet) 285.1 ft 52 Deck Width, Out-to-Out (e.g. in feet) 37.4 ft 60 Substructure 5 61 Channel and Channel Protection 7 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 17% 113 Scour Critical Bridges (2002 NBI Guidelines) 8
NCHRP 24-25 Page 182 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 1 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 10,663 ft2; Cost per unit area: 65 $/ft2; Cost Multiplier: 2.0 $1,386,190.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠183 Value of time per adult * Use Table 3 ($/hr) ⧠$6.65 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠10 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $7,000/unit Estimated cost of installing scour countermeasures $88,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $6,015.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $10,808.00
NCHRP 24-25 Page 183 Phase II Appendices Scour Management Evaluation 5. State Road 37 over N Fork Alafia River Bridge 160063 in Mulberry, FL was constructed in 1951 and supports an urban minor arterial class road. This bridgeâs foundation is known with an NBI item 113 rating of â8â (Analysis: stable; Survey: stable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports an urban minor arterial, but it is not an emergency evacuation route and does not provide direct access to emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for an urban minor arterial class bridge, according to the guidelines, is 0.0002 â the maximum annual probability of failure allowed for this bridge. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 16 Urban minor arterial classification NBI item 71 (bridge survey) 8 Waterway is equal to the desirable criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 5 Foundation is in fair condition NBI item 61 (bridge survey) 7 Channel has some minor drift and damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge does not meet the minimum performance level because the annual probability of failure is greater than 0.0002. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. But if the foundation was unknown it would not meet the minimum performance level. Thus, if it had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known.
NCHRP 24-25 Page 184 Phase II Appendices 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 185 Phase II Appendices Bridge #6 The Initial Survey Respondent Information Name Manuel H. Luna, EIT E-mail Address manuel.luna@dot.state.fl.us Job Title: Project Coordinator Phone(813) 744-6050 Cell (813) 323-1150 Job Description (In what way does your job involve bridge maintenance?) Project Coordinator for Scour Project, Paint Project and Bridge Management. Review Scour Reports, Conduct Quarterly Interdisciplinary Scour Meetings, prepared Biannual Federal Scour Reports. Certified Bridge Inspector, perform bridge inspection, review inspection reports, construction plan. Prepare bridge deficiencies list and assist project manager by conducting edit check of bridge data base. Write my own computer programs to accomplish this task. Mailing Address FDOT Department Of Transportation 2916 Leslie Road Tampa, FL 33619 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Bridge No. 100352 (Parallel to Bridge No. 100353) I-75 NB over Little Manatee River In Hillsborough County
NCHRP 24-25 Page 186 Phase II Appendices National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 12 5 Inventory Route 00075 8 Structure Number 100352 19 Bypass, Detour Length (e.g. in miles) 0.6214 26 Functional Classification of Inventory Route 01 27 Year Built 1981 29 Average Daily Traffic 31000 49 Structure Length (e.g. in feet) 1391.083 52 Deck Width, Out-to-Out (e.g. in feet) 58.80 60 Substructure 8 61 Channel and Channel Protection 7 71 Waterway Adequacy 9 109 Average Daily Truck Traffic 20% 113 Scour Critical Bridges (2002 NBI Guidelines) 7
NCHRP 24-25 Page 187 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) x Simple Span(s) Â Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 54 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: _81804.95______ft2; Cost per unit area: _$110_______$/ft2; Cost Multiplier: __2______ $ 17,997,089.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile x Truck running cost $1.30 per mile x Duration of detour * Use Table 2 (days) x 183 Value of time per adult * Use Table 3 ($/hr) x $6.65 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 5 Cost for each life lost $500,000 x 2,500,000.00 * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $64,000.00 per unit Estimated cost of installing scour countermeasures $ 187,784 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $4,500.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $8,000.00
NCHRP 24-25 Page 188 Phase II Appendices Scour Management Evaluation 6. I-75 NB over Little Manatee River Bridge 100352 in Hillsborough County, FL was constructed in 1981 and supports a rural interstate. This bridgeâs foundation is known with an NBI item 113 rating of â7â (scour countermeasures installed make it stable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor arterial class bridge, according to the guidelines, is 0.0001 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 1 Rural interstate classification NBI item 71 (bridge survey) 9 Waterway is better than the desirable criteria â´Overtopping Frequency (guidelines) R Remote (once in more than 100 years) NBI item 60 (bridge survey) 8 Foundation is in very good condition NBI item 61 (bridge survey) 7 Channel has some minor drift and damage â´Scour Vulnerability (guidelines) 7 Countermeasures were installed and is now stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge does not meet the minimum performance level because the annual probability of failure is greater than 0.0001. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. But if the foundation was unknown it would not meet the minimum performance level. Thus, if it had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known.
NCHRP 24-25 Page 189 Phase II Appendices 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 190 Phase II Appendices Bridge #7 The Initial Survey Respondent Information Name Manuel H. Luna, EIT E-mail Address manuel.luna@dot.state.fl.us Job Title : Project Coordinator Phone(813) 744-6050 Cell (813) 323-1150 Job Description (In what way does your job involve bridge maintenance?) Project Coordinator for Scour Project, Paint Project and Bridge Management. Review Scour Reports, Conduct Quarterly Interdisciplinary Scour Meetings, prepared Biannual Federal Scour Reports. Certified Bridge Inspector, perform bridge inspection, review inspection reports, construction plan. Prepare bridge deficiencies list and assist project manager by conducting edit check of bridge data base. Write my own computer programs to accomplish this task. Mailing Address FDOT Department Of Transportation 2916 Leslie Road Tampa, FL 33619 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. US-301 over Hillsborough River National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 12 5 Inventory Route 00301 8 Structure Number 100434 19 Bypass, Detour Length (e.g. in miles) 19.88 26 Functional Classification of Inventory Route 02 27 Year Built 1985 29 Average Daily Traffic 10900 49 Structure Length (e.g. in feet) 451.43 52 Deck Width, Out-to-Out (e.g. in feet) 47.50 60 Substructure 8 61 Channel and Channel Protection 7 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 10% 113 Scour Critical Bridges (2002 NBI Guidelines) 7
NCHRP 24-25 Page 191 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) X Simple Span(s) Â Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 54 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: _21444_______ft2; Cost per unit area: _110.00_______$/ft2; Cost Multiplier: ___2_____ $ 4,717,680.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile x Truck running cost $1.30 per mile x Duration of detour * Use Table 2 (days) x 183 Value of time per adult * Use Table 3 ($/hr) x $6.65 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 5 Cost for each life lost $500,000 x 2,500,000.00 * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $ 50,000.00 Estimated cost of installing scour countermeasures $ 120,823.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $ 4,500.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $ 8,000.00
NCHRP 24-25 Page 192 Phase II Appendices Scour Management Evaluation 7. US 301 over Hillsborough River Bridge 100434 in Hillsborough County, FL was constructed in 1985 and supports an rural principal arterial class road. This bridgeâs foundation is known with an NBI item 113 rating of â7â (scour countermeasures installed make it stable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports an urban principal arterial road, which has significant economic value and may provide access to critical local services. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. However, this bridge has significant economic value and may provide critical access to local services. Thus, if this bridge had an unknown foundation the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 193 Phase II Appendices Bridge #8 The Initial Survey Respondent Information Name Manuel H. Luna, EIT E-mail Address manuel.luna@dot.state.fl.us Job Title Structure Project Coordinator Phone (813) 744-6050 Cell (813) 323-1150 Job Description (In what way does your job involve bridge maintenance?) Project Coordinator for Scour Project, Paint Project and Bridge Management. Review Scour Reports, Conduct Quarterly Interdisciplinary Scour Meetings, prepared Biannual Federal Scour Reports. Certified Bridge Inspector, perform bridge inspection, review inspection reports, construction plan. Prepare bridge deficiencies list and assist project manager by conducting edit check of bridge data base. Write my own computer programs to accomplish this task. Mailing Address FDOT Department Of Transportation 2916 Leslie Road Tampa, FL 33619 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Bridge Number150107, the Howard Frankland is a tidal bridge constructed in 1959 and widened in 1992, 316 spans. This structure serves as the Northbound crossing of SR-93/I-275 over Old Tampa Bay The maximum computed 100 and 500 year scour depths for this bridge are 27.5 feet and 29.5 feet respectively, which make the structure low risk, high priority. An accurate determination of the pile tip elevation is recommended, thus it may eliminate the need for a Phase 4 scour assessment or countermeasure according to our scour consultant, Pitman Hartenstein & associates,( PH&A)
NCHRP 24-25 Page 194 Phase II Appendices National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI Database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 12 5 Inventory Route 00275 8 Structure Number 150107 19 Bypass, Detour Length (e.g. in miles) 0.6 26 Functional Classification of Inventory Route 11 27 Year Built 1959 29 Average Daily Traffic 67250 49 Structure Length (e.g. in feet) 15872 52 Deck Width, Out-to-Out (e.g. in feet) 62.3 60 Substructure 5 61 Channel and Channel Protection 7 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 8% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 195 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) X Simple Span(s) Â Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed Estimated 25 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: _988,922.13 ft2; Cost per unit area: __110.00__$/ft2; Cost Multiplier: 2.0__ $ 219,762,868.60 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile X Truck running cost $1.30 per mile X Duration of detour * Use Table 2 (days) X 183 Value of time per adult * Use Table 3 ($/hr) x $6.65 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 10 Cost for each life lost $500,000 x $2,500,000 * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $ 50,000.00 per Unit Estimated cost of installing scour countermeasures $ 156,300/first bent Articulating block Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) Dispersive Wave $1000 per bent . For the first boring the cost is app.$11,000. Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $ 8,000.00 to 10,000.00
NCHRP 24-25 Page 196 Phase II Appendices Scour Management Evaluation 8. I-275 NB over Tampa Bay Bridge 150107 in Pinellas County, FL was constructed in 1959 and supports an urban interstate. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports an urban interstate, but it is not an emergency evacuation route and does not provide direct access to emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for an urban minor arterial class bridge, according to the guidelines, is 0.0001 â the maximum annual probability of failure allowed for this bridge. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 11 Urban interstate classification NBI item 71 (bridge survey) 8 Waterway is equal to the desirable criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 5 Foundation is in fair condition NBI item 61 (bridge survey) 7 Channel has some minor drift and damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge does not meet the minimum performance level because the annual probability of failure is greater than 0.0001. Recommended management strategy This bridge does not meet the minimum performance level. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 197 Phase II Appendices Bridge #9 The Initial Survey Respondent Information Name Manuel H. Luna, EIT E-mail Address manuel.luna@dot.state.fl.us Job Title Structure Project Coordinator Phone : (813) 744-6050 Job Description (In what way does your job involve bridge maintenance?) Project Coordinator for Scour Project, Paint Project and Bridge Management. Review Scour Reports, Conduct Quarterly Interdisciplinary Scour Meetings, prepared Biannual Federal Scour Reports. Certified Bridge Inspector, perform bridge inspection, review inspection reports, construction plan. Prepare bridge deficiencies list and assist project manager by conducting edit check of bridge data base. Write my own computer programs to accomplish this task. Mailing Address FDOT Department Of Transportation 2916 Leslie Road Tampa, FL 33619 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Bridge 100039 the US-41 SB over Little Manatee River is a 759 feet long bridge with 15 spans. It was built in 1971. The little manatee river is a tidally influence river. The calculated maximum water velocity is 10.42 fps. A geotechnical assessment is required given the unknown pile tip elevation. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 12 5 Inventory Route 00041 8 Structure Number 100039 19 Bypass, Detour Length (e.g. in miles) 0.6214 26 Functional Classification of Inventory Route 02 27 Year Built 1971 29 Average Daily Traffic 8250 49 Structure Length (e.g. in feet) 758.85 52 Deck Width, Out-to-Out (e.g. in feet) 43.90 60 Substructure 7 61 Channel and Channel Protection 8 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 12% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 198 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) x Simple Span(s) Â Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed App. 40 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: _33319.24 __ft2; Cost per unit area: _60____$/ft2; Cost Multiplier: 2.0______ $ 39,983,308.80 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile X Truck running cost $1.30 per mile x Duration of detour * Use Table 2 (days) x 183 Value of time per adult * Use Table 3 ($/hr) x $6.65 Average car occupancy rate 1.63 people x Value of time for trucks $22.01 per hour x Average detour speed 40 miles per hour x Number of deaths from failure * Use Table 2 (Number of people) x 5 Cost for each life lost $500,000 x 2,500,000 * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $ 50,000.00 per Unit Estimated cost of installing scour countermeasures $172.00 per Square Yard Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $4,500.00 Initial borings Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $8,000.00
NCHRP 24-25 Page 199 Phase II Appendices Scour Management Evaluation 9. US 41 SB over Little Manatee River Bridge 100039 in Ruskin, FL was constructed in 1971 and supports a rural principal arterial class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural principal arterial road, which has significant economic value and may provide access to critical local services. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has significant economic value and may provide critical access to local services. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 200 Phase II Appendices Bridge #10 The Initial Survey Respondent Information Name Manuel H. Luna, EIT E-mail Address manuel.luna@dot.state.fl.us Job Title: Project Coordinator Phone(813) 744-6050 Cell (813) 323-1150 Job Description (In what way does your job involve bridge maintenance?) Project Coordinator for Scour Project, Paint Project and Bridge Management. Review Scour Reports, Conduct Quarterly Interdisciplinary Scour Meetings, prepared Biannual Federal Scour Reports. Certified Bridge Inspector, perform bridge inspection, review inspection reports, construction plan. Prepare bridge deficiencies list and assist project manager by conducting edit check of bridge data base. Write my own computer programs to accomplish this task. Mailing Address FDOT Department Of Transportation 2916 Leslie Road Tampa, FL 33619 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Bridge No. 100100 is a three spans, 321 feet long bridge, skew 20 degree , that was constructed in 1913 and reconstructed in 1994, as East/West crossing of SR-60 over the Hillsborough River. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 12 5 Inventory Route 00060 8 Structure Number 100100 19 Bypass, Detour Length (e.g. in miles) 1.8642 26 Functional Classification of Inventory Route 14 27 Year Built 1913 29 Average Daily Traffic 36500 49 Structure Length (e.g. in feet) 322.89 52 Deck Width, Out-to-Out (e.g. in feet) 77.99 60 Substructure 6 61 Channel and Channel Protection 8 71 Waterway Adequacy 7 109 Average Daily Truck Traffic 5% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 201 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) Movable Bascule Bridge x Simple Span(s) Â Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 63 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: _25189.45_______ft2; Cost per unit area: __$1500______$/ft2; Cost Multiplier: ___2.0_____ $ 78,568,380.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile X Truck running cost $1.30 per mile X Duration of detour * Use Table 2 (days) X 183 Value of time per adult * Use Table 3 ($/hr) X $6.65 Average car occupancy rate 1.63 people X Value of time for trucks $22.01 per hour X Average detour speed 40 miles per hour X Number of deaths from failure * Use Table 2 (Number of people) X 5 Cost for each life lost $500,000 X 2,500,000 * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $64,000.00 Estimated cost of installing scour countermeasures $172.00 per SY Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $4,500.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $ 8,000.00
NCHRP 24-25 Page 202 Phase II Appendices Scour Management Evaluation 10. State Route 60 over Hillsborough River Bridge 100100 in Tampa, FL was constructed in 1913 and supports an urban principal arterial class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports an urban principal arterial road, which has significant economic value and may provide access to critical local services. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has significant economic value and may provide critical access to local services. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 203 Phase II Appendices Response to Evaluations Richard Semple commented on the first five management summaries, which we submitted. He said: I've reviewed the first five case studies, since those are the ones I submitted. The comments are inclusive to all five, in as much as the "Recommended Management Strateg[ies]" are all the same. The approach presented seems logical and is along the lines of our approach for determining the stability of "unknown foundation" bridges, with the goal to eliminate them from this criteria based on field reconnaissance and foundation investigation. At the present time, we're doing some select SPT borings, to determine soil resistance and using a similar bridge with known foundation and location, make a determination if the bridge can be reclassified from "unknown to "known" foundation. The concern in using "risk based management" is the fact that youâre going "out on a limb" based on faith in your calculations. The one good thing that we have going for our situation is the relative slow flow of water and historical inspection data for our unknown foundation structures. Manuel Luna commented on the last five management summaries, which he submitted. He and others correctly note that bridge numbers 150107 and 100352 should have been classified as high priority structures. Fortunately this mistake did not change the management summary in either case, and illustrates the conservatism of the scour guidelines regarding high ADT bridges. His full comments and questions are as follows: 1. I have some questions as far as the Howard Frankland Bridge (Br. No. 150107), which is classified as not a high priority bridge. I would like you to explain what is a high priority bridge? Since, this bridge is on the National Highway System and it is on the STRAHNET Highway designation with a pretty high ADT, and yet is not considered high priority bridge. Why?
NCHRP 24-25 Page 204 Phase II Appendices 2. According to our scour consultant, Hisham Sunna, he said the following: "Although the Parallel Seismic method is very reliable for determining pile embedments, it is a costly method and one of the most field labor-intensive." Do you recommend any other method besides Parallel Seismic method to make an unknown foundation bridge known? 3. Hisham Sunna also questions the priority on the following bridge as follows: "I-75 NB over Little Manatee River. The statement is that it is not a high priority bridge because it is a rural route; we believe since I-75 is an evacuation route, as are most major N-S arterials in Florida, that it is a high priority bridge." Please explain. 4. Another question that I have is, why all the recommended Management Strategies are the same? Are there any other methods that can be used to make an unknown foundation bridge known? I do agree with Richard when he said: "The approach presented seems logical and it is along the lines of our approach for determining the stability of unknown foundation bridges in District 1 and 7." 5. As you can see we have some reservation in your prioritization method for some of our bridges, such as the Howard Frankland and The Little Manatee River, also you do not mention any historical data for ground elevation comparison, and how it can be used to assign level of risk for the unknown foundation bridges. As for the revering bridges in both Districts 1 and 7 the one good thing that we have in Florida is the relative slow flow of water and our historical data for ground elevation comparison for our unknown foundation structures over several years.
NCHRP 24-25 Page 205 Phase II Appendices New York Bridges Bridge #1 The Initial Survey Respondent Information Name Bob Burnett E-mail Address bburnett@dot.state.ny.us Job Title Director, Geotech. Eng. Phone 518-457-4712 Job Description (In what way does your job involve bridge maintenance?) We do foundations. Mike Sullivan, in our Structures Division Inventory Unit, completed the survey. Mailing Address 50 Wolf Road, MP 31 Albany, NY 12232 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. County Road 1 over South Branch of Van Campen Creek. Town of Friendship, NY, NYSDOT Region 6 (Hornell), County 1 (Allegany). Not critical structure. Failed 8/2003. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 62 5 Inventory Route 140000000 8 Structure Number 000000003330270 19 Bypass, Detour Length (e.g. in miles) 4 (km) 26 Functional Classification of Inventory Route 07 27 Year Built 1957 29 Average Daily Traffic 689 49 Structure Length (e.g. in feet) 32.92 (m) 52 Deck Width, Out-to-Out (e.g. in feet) 9.14 (m) 60 Substructure 4 61 Channel and Channel Protection 6 71 Waterway Adequacy 6 109 Average Daily Truck Traffic 8% 113 Scour Critical Bridges (2002 NBI Guidelines) *3 * Bridge was coded â3â. Scour Critical for Item 113 before it failed due to scour at pier in 8/2003. Bridge was replaced with a new single span prestressed concrete structure in 2004.
NCHRP 24-25 Page 206 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 46 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $571,300 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠548 Value of time per adult * Use Table 3 ($/hr) ⧠$8.59 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $30,000 Estimated cost of installing scour countermeasures $25,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $0 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $25,000
NCHRP 24-25 Page 207 Phase II Appendices Scour Management Evaluation 1. County Road 1 over South Branch of Van Campen Creek Bridge 3330270 in Friendship, NY (Allegany County) was constructed in 1930. It supported a rural major collector class road before it failed due to scour in 2003. All of the data reported for this bridge was collected prior to failure and NBI item 113 was coded â3â (Scour critical and unstable). To test the guidelines, this bridge will be evaluated as if it had an unknown foundation. Is it a high-priority bridge? This bridge supported a rural road, which was not a principal arterial, emergency route, and does not provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural major collector class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 7 Rural major collector classification NBI item 71 (bridge survey) 6 Waterway exceeds than the minimum criteria â´Overtopping Frequency (guidelines) O Occasional (once in 3-10 years) NBI item 60 (bridge survey) 4 Foundation is in poor condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 4 Analysis: stable; Survey: exposed foundation â´Annual probability of failure (guidelines) 0.0005 A 1 in 3,030 chance of failure in any given year This bridge does not meet the minimum performance level because the annual probability of failure is not less than 0.0005. Recommended management strategy This bridge does not meet the minimum performance level. Thus, if it had an unknown foundation and had been evaluated before it failed the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known.
NCHRP 24-25 Page 208 Phase II Appendices 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 209 Phase II Appendices Bridge #2 The Initial Survey Respondent Information Name Bob Burnett E-mail Address bburnett@dot.state.ny.us Job Title Director, Geotech. Eng. Phone 518-457-4712 Job Description (In what way does your job involve bridge maintenance?) Mailing Address 50 Wolf Road, MP 31 Albany, NY 12232 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Warren Farm Road over Wiccopee Creek. Town of East Fishkill, NY. NYSDOT Region 8 (Poughkeepsie), County 2 (Dutchess). Dead end road to homes. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 62 5 Inventory Route 180000000 8 Structure Number 000000002268710 19 Bypass, Detour Length (e.g. in miles) 199 (km) 26 Functional Classification of Inventory Route 09 27 Year Built 1980 29 Average Daily Traffic 200 49 Structure Length (e.g. in feet) 8.8 (m) 52 Deck Width, Out-to-Out (e.g. in feet) 7.8 (m) 60 Substructure 6 61 Channel and Channel Protection 6 71 Waterway Adequacy 5 109 Average Daily Truck Traffic 4% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 210 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 24 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $$1,513,850 70 (prestressed concrete) + 15 (demo) Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠730 Value of time per adult * Use Table 3 ($/hr) ⧠$8.54 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠1 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $20,000 Estimated cost of installing scour countermeasures $15,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $5,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $15,000
NCHRP 24-25 Page 211 Phase II Appendices Scour Management Evaluation 2. Warren Farm Road over Wiccopee Creek Bridge 2268710 in East Fishkill, NY (Dutchess County) was constructed in 1980 and supports a rural-local class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, but it is the only evacuation route for a local community. Thus, in this context this bridge is considered a high priority bridge. Recommended management strategy This bridge is a critical evacuation route and has significant economic value. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 212 Phase II Appendices Bridge #3 The Initial Survey Respondent Information Name Bob Burnett E-mail Address bburnett@dot.state.ny.us Job Title Director, Geotech. Eng. Phone 518-457-4712 Job Description (In what way does your job involve bridge maintenance?) Mailing Address 50 Wolf Road, MP 31 Albany, NY 12232 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Arbutus Road over Fishing Brook. Town of Newcomb, NY. NYSDOT Region 1 (Albany), County 2 (Essex). Dead-end road to homes National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 62 5 Inventory Route 118000000 8 Structure Number 000000002268950 19 Bypass, Detour Length (e.g. in miles) 199 (km) 26 Functional Classification of Inventory Route 09 27 Year Built 1950 29 Average Daily Traffic 100 49 Structure Length (e.g. in feet) 16.1 (m) 52 Deck Width, Out-to-Out (e.g. in feet) 4.5 (m) 60 Substructure 6 61 Channel and Channel Protection 7 71 Waterway Adequacy 5 109 Average Daily Truck Traffic 6% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 213 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 10years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $340,808 70 (prestressed concrete) + 15 (demo) Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠730 Value of time per adult * Use Table 3 ($/hr) ⧠$8.54 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠1 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $20,000 Estimated cost of installing scour countermeasures $15,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $5,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $15,000
NCHRP 24-25 Page 214 Phase II Appendices Scour Management Evaluation 3. Arbutus Road over Fishing Brook Bridge 2268950 in Newcomb, NY (Essex County) was constructed in 1950 and supports a rural local class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, but it is the only evacuation route for a local community. Thus, in this context this bridge is considered a high priority bridge. Recommended management strategy This bridge is a critical evacuation route and has significant economic value. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 215 Phase II Appendices Bridge #4 The Initial Survey Respondent Information Name Bob Burnett E-mail Address bburnett@dot.state.ny.us Job Title Director, Geotech. Eng. Phone 518-457-4712 Job Description (In what way does your job involve bridge maintenance?) Mailing Address 50 Wolf Road, MP 31 Albany, NY 12232 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Route 23 over CSX/Amtrak/Hudson River âRip Van Winkle Bridgeâ. Village of Catskill, NY, NYSDOT Region 1 (Albany), County 3 (Greene). Critical National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 62 5 Inventory Route 131000230 8 Structure Number 000000005017820 19 Bypass, Detour Length (e.g. in miles) 64 (km) 26 Functional Classification of Inventory Route 14 27 Year Built 1935 29 Average Daily Traffic 13609 49 Structure Length (e.g. in feet) 1536.1 (m) 52 Deck Width, Out-to-Out (e.g. in feet) 11.2 (m) 60 Substructure 6 61 Channel and Channel Protection 8 71 Waterway Adequacy 6 109 Average Daily Truck Traffic 5% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 216 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one)  Simple Span(s) ⧠Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 29 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $31,956,192 120 + 15 (demo) Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠183 Value of time per adult * Use Table 3 ($/hr) ⧠$8.59 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠10 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $150,000 Estimated cost of installing scour countermeasures $150,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $50,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $50,000
NCHRP 24-25 Page 217 Phase II Appendices Scour Management Evaluation 4. Route 23 over Hudson River (âRip Van Winkle Bridgeâ) Bridge 5017820 in Catskill, NY (Albany County) was constructed in 1935 and supports an urban principal arterial class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is a principal arterial and provides direct access to emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge provides critical access to local services and has significant economic value. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 218 Phase II Appendices Bridge #5 The Initial Survey Respondent Information Name Bob Burnett E-mail Address bburnett@dot.state.ny.us Job Title Director, Geotech. Eng. Phone 518-457-4712 Job Description (In what way does your job involve bridge maintenance?) Rockway Turnpike over Mott Creek. Town of Hempstead (Long Island). NYSDOT Region 10 (Hauppauge), County 1 (Nassau). Not critical Mailing Address 50 Wolf Road, MP 31 Albany, NY 12232 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 62 5 Inventory Route 140000000 8 Structure Number 000000003300120 19 Bypass, Detour Length (e.g. in miles) 16 (km) 26 Functional Classification of Inventory Route 14 27 Year Built 1993 29 Average Daily Traffic 33,850 49 Structure Length (e.g. in feet) 39.9 (m) 52 Deck Width, Out-to-Out (e.g. in feet) 34.0 (m) 60 Substructure 8 61 Channel and Channel Protection 6 71 Waterway Adequacy 5 109 Average Daily Truck Traffic 3% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 219 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 37years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $2,446,688 70 (prestressed concrete) + 15 (demo) Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠183 Value of time per adult * Use Table 3 ($/hr) ⧠$8.59 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠10 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $80,000 Estimated cost of installing scour countermeasures $30,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $25,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $25,000
NCHRP 24-25 Page 220 Phase II Appendices Scour Management Evaluation 5. Rockway Turnpike over Mott Creek Bridge 3300120 in Hempstead, NY (Nassau County) was constructed in 1993 and supports an urban principal arterial class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports an urban principal arterial, which has significant economic value and may provide access to critical local services. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has significant economic value and may provide critical access to local services. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 221 Phase II Appendices Bridge #6 The Initial Survey Respondent Information Name Bob Burnett E-mail Address bburnett@dot.state.ny.us Job Title Director, Geotech. Eng. Phone 518-457-4712 Job Description (In what way does your job involve bridge maintenance?) Mailing Address 50 Wolf Road, MP 31 Albany, NY 12232 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Pearl Street over Mill River. Town of Hempstead (Long Island). NYSDOT Region 10 (Hauppauge), County 1 (Nassau. Not critical. 4 piers + abutments National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 62 5 Inventory Route 140000000 8 Structure Number 000000003330150 19 Bypass, Detour Length (e.g. in miles) 1 (km) 26 Functional Classification of Inventory Route 17 27 Year Built *1932 29 Average Daily Traffic 10050 49 Structure Length (e.g. in feet) 49.6 m) 52 Deck Width, Out-to-Out (e.g. in feet) 18.2 (m) 60 Substructure 5 61 Channel and Channel Protection 6 71 Waterway Adequacy 4 109 Average Daily Truck Traffic 2% 113 Scour Critical Bridges (2002 NBI Guidelines) U *superstructure replaced 1986.
NCHRP 24-25 Page 222 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 30 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $1,603,836 70 (prestressed concrete) + 15 (demo) Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠183 Value of time per adult * Use Table 3 ($/hr) ⧠$8.59 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠5 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $120,000 Estimated cost of installing scour countermeasures $45,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $40,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $25,000
NCHRP 24-25 Page 223 Phase II Appendices Scour Management Evaluation 6. Pearl Street over Mill River Bridge 3330150 in Hempstead, NY was constructed in 1930 and supports an urban collector class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports an urban road, which is not a principal arterial or emergency evacuation route, and does not provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for an urban collector class bridge, according to the guidelines, is 0.0002 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 17 Urban collector classification NBI item 71 (bridge survey) 4 Waterway meets the minimum limits for no action â´Overtopping Frequency (guidelines) O Occasional (once in 3-10 years) NBI item 60 (bridge survey) 5 Foundation is in fair condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 5 Analysis: stable; Survey: scour is within limits â´Annual probability of failure (guidelines) 0.00004 A 1 in 25,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (30 years, according to the survey respondent) as follows:1-(1-0.00004)30, or about 0.0012 (a 1 in 833 chance of failure in the next 30 years). This and other survey data are now used to calculate the risk of death as follows: 998,2$)5()/000,500($)/0012.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $120,000 and the risk of death is $2,998, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 224 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $45,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $1,603,836. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 330,515$ )183()/050,10()6.0( 100 2/30.1$ 100 21/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 687,390$ /40 )183()/050,10()6.0( 100 2)/01.22($ 100 21)63.1()/59.8($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $5,009,853. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $6,008. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures. However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 225 Phase II Appendices Bridge #7 The Initial Survey Respondent Information Name Bob Burnett E-mail Address bburnett@dot.state.ny.us Job Title Director, Geotech. Eng. Phone 518-457-4712 Job Description (In what way does your job involve bridge maintenance?) Mailing Address 50 Wolf Road, MP 31 Albany, NY 12232 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Interstate 90 over CSX/Hudson River âPatroon Island Bridgeâ. City of Albany, NY. NYSDOT Region 1 (Albany), County 1 (Albany). Critical National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 62 5 Inventory Route 111000900 8 Structure Number 000000001092839 19 Bypass, Detour Length (e.g. in miles) 7 (km) 26 Functional Classification of Inventory Route 11 27 Year Built 1968 29 Average Daily Traffic 75196 49 Structure Length (e.g. in feet) 547.1 (m) 52 Deck Width, Out-to-Out (e.g. in feet) 27.1 (m) 60 Substructure 6 61 Channel and Channel Protection 8 71 Waterway Adequacy 6 109 Average Daily Truck Traffic 9% 113 Scour Critical Bridges (2002 NBI Guidelines) 8
NCHRP 24-25 Page 226 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one)  Simple Span(s) ⧠Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 27years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $12,752,112 120 + 15 (Demo) Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠183 Value of time per adult * Use Table 3 ($/hr) ⧠$8.59 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠10 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $180,000 Estimated cost of installing scour countermeasures $150,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000* Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $50,000 *We know that the channel piers have spread footings on rock. We do not know how resilient the rock layer is to scour. You could enter â0â here as we do know all footing elevations for this structure.
NCHRP 24-25 Page 227 Phase II Appendices Scour Management Evaluation 7. Interstate 90 over Hudson River (âPatroon Island Bridgeâ) Bridge 1092839 in Albany, NY (Albany County) was constructed in 1968 and supports an urban interstate. This bridgeâs foundation is known with an NBI item 113 rating of â8â (Analysis: stable; Survey: stable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports an urban interstate, which is emergency evacuation route, and provides direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. This bridge provides critical access to local services and has significant economic value. Thus, if this bridge had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 228 Phase II Appendices Bridge #8 The Initial Survey Respondent Information Name Bob Burnett E-mail Address bburnett@dot.state.ny.us Job Title Director, Geotech. Eng. Phone 518-457-4712 Job Description (In what way does your job involve bridge maintenance?) Mailing Address 50 Wolf Road, MP 31 Albany, NY 12232 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Peace Bridge over I-190/Niagara River, City of Buffalo, NY. NYSDOT Region 5 (Buffalo), County 3 (Erie). Critical. Reconstructed in 1989. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 62 5 Inventory Route 181000000 8 Structure Number 000000005516290 19 Bypass, Detour Length (e.g. in miles) 64 (km) 26 Functional Classification of Inventory Route 12 27 Year Built 1927 29 Average Daily Traffic 17,000 49 Structure Length (e.g. in feet) 1218.5 (m) 52 Deck Width, Out-to-Out (e.g. in feet) 11.9 (m) 60 Substructure 6 61 Channel and Channel Protection 9 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 9% 113 Scour Critical Bridges (2002 NBI Guidelines) 6
NCHRP 24-25 Page 229 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 13years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $52,277,160 120 + 15 (demo) Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠183 Value of time per adult * Use Table 3 ($/hr) ⧠$8.59 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠5 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $100,000 Estimated cost of installing scour countermeasures $100,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $0 (known) Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $50,000
NCHRP 24-25 Page 230 Phase II Appendices Scour Management Evaluation 8. Peace Bridge over Niagara River Bridge 5516290 in Buffalo, NY (Erie County) was constructed in 1927 and supports an urban freeway. This bridgeâs foundation is known with an NBI item 113 rating of â6â (not yet evaluated, but probably stable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports an urban freeway, which is provides direct access to emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. This bridge provides critical access to local services and has significant economic value. Thus, if this bridge had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 231 Phase II Appendices Bridge #9 The Initial Survey Respondent Information Name Bob Burnett E-mail Address bburnett@dot.state.ny.us Job Title Director, Geotech. Eng. Phone 518-457-4712 Job Description (In what way does your job involve bridge maintenance?) Mailing Address 50 Wolf Road, MP 31 Albany, NY 12232 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Route 42 over Shingle Kill. Town of Deer Park, NY. NYSDOT Region 8 (Poughkeepsie), County 3 (Orange). Not critical National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 62 5 Inventory Route 131000420 8 Structure Number 000000001024960 19 Bypass, Detour Length (e.g. in miles) 48 (km) 26 Functional Classification of Inventory Route 14 27 Year Built 1956 29 Average Daily Traffic 7895 49 Structure Length (e.g. in feet) 16.7 (m) 52 Deck Width, Out-to-Out (e.g. in feet) 12.6 (m) 60 Substructure 4 61 Channel and Channel Protection 5 71 Waterway Adequacy 4 109 Average Daily Truck Traffic 5% 113 Scour Critical Bridges (2002 NBI Guidelines) 8
NCHRP 24-25 Page 232 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 23years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $444,049 75 (steel-simple span) + 15 (demo) Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠183 Value of time per adult * Use Table 3 ($/hr) ⧠$8.59 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠10 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $20,000 Estimated cost of installing scour countermeasures $15,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $0 (known) Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $25,000
NCHRP 24-25 Page 233 Phase II Appendices Scour Management Evaluation 9. Route 42 over Shingle Kill Bridge 1024960 in Deer Park, NY (Orange County) was constructed in 1956 and supports an urban principal arterial roadway. This bridge has a known foundation with an NBI item 113 rating of â8â (Analysis: stable; Survey: stable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports an urban principal arterial, which has significant economic significance. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. This bridge provides critical access to local services and has significant economic value. Thus, if this bridge had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 234 Phase II Appendices Bridge #10 The Initial Survey Respondent Information Name Bob Burnett E-mail Address bburnett@dot.state.ny.us Job Title Director, Geotech. Eng. Phone 518-457-4712 Job Description (In what way does your job involve bridge maintenance?) Mailing Address 50 Wolf Road, MP 31 Albany, NY 12232 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. County Road 155 over East Branch Cheningo Creek. Town of Cuyler, NY. NYSDOT Region 3 (Syracuse), County 2 (Cortland). Not critical National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 62 5 Inventory Route 140000000 8 Structure Number 000000003312460 19 Bypass, Detour Length (e.g. in miles) 14 (km) 26 Functional Classification of Inventory Route 09 27 Year Built 1983 29 Average Daily Traffic 79 49 Structure Length (e.g. in feet) 15.8 (m) 52 Deck Width, Out-to-Out (e.g. in feet) 7.9 (m) 60 Substructure 4 61 Channel and Channel Protection 6 71 Waterway Adequacy 4 109 Average Daily Truck Traffic 5% 113 Scour Critical Bridges (2002 NBI Guidelines) 8
NCHRP 24-25 Page 235 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 17years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $$229,216 70 + 15 (demo) Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠$1095 Value of time per adult * Use Table 3 ($/hr) ⧠$8.59 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠0 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $30,000 Estimated cost of installing scour countermeasures $20,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $0 (known) Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $15,000
NCHRP 24-25 Page 236 Phase II Appendices Scour Management Evaluation 10. County Road 155 over East Branch Cheningo Creek Bridge 3312460 in Cuyler, NY was constructed in 1983 and supports a rural local class road. This bridge has a known foundation with an NBI item 113 rating of â8â (Analysis: stable; Survey: stable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency evacuation route, and does not provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural local class bridge, according to the guidelines, is 0.002 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 9 Rural local classification NBI item 71 (bridge survey) 4 Waterway meets the minimum limits for no action â´Overtopping Frequency (guidelines) O Occasional (once in 3-10 years) NBI item 60 (bridge survey) 4 Foundation is in poor condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 4 Analysis: stable; Survey: foundation is exposed â´Annual probability of failure (guidelines) 0.0006 A 1 in 1,667 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.002. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (17 years, according to the survey respondent) as follows:1-(1-0.0006)17, or about 0.01 (a 1 in 100 chance of failure in the next 17 years). This and other survey data are now used to calculate the risk of death as follows: 0$)0()/000,500($)/01.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $30,000 and the risk of death is $0, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 237 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $20,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $229,216. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 652,370$ )1095()/79()7.8( 100 5/30.1$ 100 51/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 973,270$ /40 )1095()/79()7.8( 100 5)/01.22($ 100 51)63.1()/59.8($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages Since the cost of death is probably negligible, the total cost of bridge failure totals $870,842. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $8,840. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. However, if this bridge had an unknown foundation the guidelines would have strongly recommended that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 238 Phase II Appendices Response to Evaluations Robert Burnett, the acting director of the NY geotechnical engineering bureau, was the first to comment on the management summaries. He said: The recommendation to investigate the foundation, preferably using parallel seismic, followed by a scour analysis and possibly countermeasures came out far too frequently for the very diverse group of examples that we sent. The "value" of the structure to the transportation system does not seem to be properly accounted for, given that three absolutely crucial structures (Interstate 90 over the Hudson River, Peace Bridge over the Niagara River to Canada, The Rip Van Winkle Bridge over the Hudson) over two major rivers received the same advice as County Route 1 over Van Campen Creek. CR1 could be closed with hardly a ripple to the system and should not warrant even a minor effort to save it. The Peace Bridge to Canada is a major economic link and would certainly deserve an all-out investigation and mitigation project. The age of the structure and therefore its remaining life should also be a factor in economic decisions. Some of these bridges are less than 25 years old and some are more than fifty, some even 70, so our investment in them should take that into account. Yet, similar recommendations are made for many of them, as well. Is the structure condition and likely remaining life considered before the cost of the fix is proposed? One specific comment: I didn't understand how the risk of death from failure could be zero for County Route 155 over East Branch Cheningo Creek. No one uses this bridge? Mr. Burnettâs comments regarding the correlation between a bridgeâs suggested risk management plan and its priority (i.e. functional importance) highlight an important aspect of the scour risk guidelines. The implication of his comments is that County Route 1, which has a lower priority than the Peace or Rip Van Winkle bridges, should have a different
NCHRP 24-25 Page 239 Phase II Appendices management plan than these two high-priority bridges. He then suggests that the remaining life and the associated economics of the bridge should have changed these assessments. However, for the sake of clarity, Table 17 shows a comparison of these bridges with some pertinent parameters. Table 17 Bridge Case Study Comparison Scour Risk Parameter County Road 1 Rip Van Winkle Peace Bridge Is it High Priority? No Yes Yes NBI Item 27 (Year Built) 1957 1935 1927 Remaining Life 46* 29 13 NBI Item 113 Code 3â U 6 Overtopping Frequency Occasional Slight Slight Scour Vulnerability 4 7 7 Annual Probability of Failure 0.0005 0.00025 0.00025 Lifetime Probability of Failure 0.023 0.0072 0.0032 Total Cost of Failure $2,399,114 $121,461,054 $165,539,757 Does it Pass the MPL? No No No * This was the age of the bridge when it failed in August 2003. â This was the NBI code before the bridge failed. The first thing to note is that none of these three bridges passed their respective MPLâs, and the last two did not pass the high-priority test, which effectively supersedes the MPL test in the guidelines. The next thing to note is that County Road 1 had a known foundation that was rated scour critical (i.e. NBI item 113 = 3) before it ultimately failed, and the scour vulnerability parameter (an estimated NBI Item 113 code) identified its poor condition. The last thing to note is that the Peace and Rip Van Winkle bridges both lack a proper scour evaluation, and that the latter has an unknown foundation. Thus, the latter two bridges would qualify for mitigation or replacement or closure because they are high priority, while County Road 1 would qualify for the same treatment due to its poor performance. In other words, both rationales are clearly worthy of concern. This underscores the fact that these guidelines have two criterions that add special conservatism to the value of these mitigation options: priority and poor performance. It also underscores the fact that the recommended risk management plans are not intended to prioritize the
NCHRP 24-25 Page 240 Phase II Appendices work schedule of at-risk bridges. The States are ultimately free to rank the work orders for at-risk bridges with unknown foundations as they see fit. Furthermore, County Road 155 had a risk of death equal to zero because its low ADT makes it very unlikely that anyone will be on the bridge if it were to fail unexpectedly. A more rigorous probabilistic model for whether someone will be on the bridge if and when if failed unexpectedly was deemed unnecessary given the uncertainty assigning a value of lost life. If a state has a better estimate for either of these aspects of casualties due to bridge failure, the guidelines allow this to be used. Mike Sullivan, a NY hydraulics engineer, also submitted comments. Two of his comments relate to a mistake in the Annual Probability of Failure table that was attached to the management summaries. This mistake was subsequently acknowledged and discussed in a later phone conversation. His comments also underscore the fact that none of the case studies ultimately had a final recommendation that advocated installing automated scour monitoring (ASM). Ten of the case studies, however, would have warranted ASM if scour countermeasures were not also warranted. Mr. Sullivanâs comments are as follows: 1) I came up with a different result for Bridge #1 (BIN 3330270 - County Road 1 over South Branch of Van Campen Creek, failed due to pier scour in 2003). When I plug the values for NBI Items 26 & 71 into Table 2, I get an Overtopping frequency = 'S' (Slight). The Annual Probability of Failure is then reduced to 0.00033 in Table 4. This would then indicate that the bridge does meet the minimum performance level because the annual probability of failure is less than 0.0005 (from Table 1). 2) Bridges 2,3,4,5,7,8, and 9 are all considered high-priority bridges and receive a Recommended Management Strategy Plan. These suggested guidelines are logical and similar to what we currently do. NYSDOT performs a Hydraulic Vulnerability
NCHRP 24-25 Page 241 Phase II Appendices Assessment for every bridge over water and the FHWA now requires an individual Plan of Action for each bridge which is coded 0, 1, 2, 3, 7, or U for Item 113. 3) I came up with a different result for Bridge #6 (Annual Probability of Failure = 0.000075 instead of 0.00004 in Table 4). This increases the "risk of death" from $2,998 to $5,619. However, this revised "risk of death" value is still much lower than the estimated cost of scour monitoring ($120,000). I spoke with [Mr.] Sedmera about this and he suggested increasing $ value/person from the default value of $500,000. I would like to see an example where the risk of death controls as compared to the cost of scour monitoring or scour countermeasures. I think it would have to be an Interstate Bridge (10 people) with an estimated remaining life of 30 years or more.
NCHRP 24-25 Page 242 Phase II Appendices North Carolina Bridges Bridge #1 The Initial Survey Respondent Information Name Mohammed Mulla E-mail Address mmulla@dot.state.nc.us Job Title Transportation Engineer Manager Phone 919-250-4088 Job Description (In what way does your job involve bridge maintenance?) Assistant State Geotechnical Engineer Mailing Address 1589 Mail Service Center Raleigh, NC 27699 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. 270011 Care County. Hubert C. Bonner Bridge. NC 12 Across Oregon Inlet. 8 miles south of Junction US 158. Critical Evacuation Route (only structure to southern Outer Banks) National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 374 5 Inventory Route 131000120 8 Structure Number 000000000550011 19 Bypass, Detour Length (e.g. in miles) 99 26 Functional Classification of Inventory Route 07 27 Year Built 1962 29 Average Daily Traffic 5100 49 Structure Length (e.g. in feet) 12865 52 Deck Width, Out-to-Out (e.g. in feet) 033.3 60 Substructure 3 61 Channel and Channel Protection 4 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 7% 113 Scour Critical Bridges (2002 NBI Guidelines) 3
NCHRP 24-25 Page 243 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 2 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 463,140 ft2; Cost per unit area: 110.00 $/ft2; Cost Multiplier: 2.0 $101.9 million Estimated cost to replace $250 million to $500 million depending on replacement alternative chosen. Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠183 Value of time per adult * Use Table 3 ($/hr) ⧠$6.72 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠5 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $10 to 20 million Estimated cost of installing scour countermeasures $100 to 200 million Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $1 million Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $200,000 to 300,000
NCHRP 24-25 Page 244 Phase II Appendices Scour Management Evaluation 1. State Road 12 over Oregon Inlet (âHubert C. Bonner Bridgeâ) Bridge 550011 in Dare County, NC was constructed in 1962. It supports a rural major collector class road. This bridgeâs foundation is known with an NBI item 113 rating of â3â (scour critical and unstable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural road, which is an emergency evacuation route. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has a known foundation, and is scheduled to be replaced very soon due to its poor condition. This bridge provides a critical emergency evacuation route for local residents and has significant economic value. Thus, if this bridge had an unknown foundation the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 245 Phase II Appendices Bridge #2 The Initial Survey Respondent Information Name Mohammed Mulla E-mail Address mmulla@dot.state.nc.us Job Title Transportation Engineer Manager Phone 919-250-4088 Job Description (In what way does your job involve bridge maintenance?) Assistant State Geotechnical Engineer Mailing Address 1589 Mail Service Center Raleigh, NC 27699 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. 730038 Pitt County. US 13 across Tar River. 0.4 miles northeast of junction NC 43 National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 374 5 Inventory Route 121000130 8 Structure Number 000000001470038 19 Bypass, Detour Length (e.g. in miles) 01 26 Functional Classification of Inventory Route 14 27 Year Built 1955 29 Average Daily Traffic 012000 49 Structure Length (e.g. in feet) 541 52 Deck Width, Out-to-Out (e.g. in feet) 029.2 60 Substructure 6 61 Channel and Channel Protection 2 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 12% 113 Scour Critical Bridges (2002 NBI Guidelines) 7
NCHRP 24-25 Page 246 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 6 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 15,797 ft2; Cost per unit area: 100.80 $/ft2; Cost Multiplier: 2.0 $3.16 million Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠183 Value of time per adult * Use Table 3 ($/hr) ⧠$6.72 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠10 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $50,000 Estimated cost of installing scour countermeasures $61,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $60,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $20,000* *have a scour report.
NCHRP 24-25 Page 247 Phase II Appendices Scour Management Evaluation 2. US Highway 13 over Tar River Bridge 1470038 in Greenville, NC was constructed in 1955 and supports an urban principal arterial class road. This bridgeâs foundation is known with an NBI item 113 rating of â7â (scour countermeasures installed make it stable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports an urban principal arterial road, and would incur significant financial damage if it were to fail. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. However, this bridge has significant economic value and may provide critical access to local services. Thus, if this bridge had an unknown foundation the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 248 Phase II Appendices Bridge #3 The Initial Survey Respondent Information Name Mohammed Mulla E-mail Address mmulla@dot.state.nc.us Job Title Transportation Engineer Manager Phone 919-250-4088 Job Description (In what way does your job involve bridge maintenance?) Assistant State Geotechnical Engineer Mailing Address 1589 Mail Service Center Raleigh, NC 27699 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. 330091 Forsyth County. ST 1001 across Yadkin River. 0.8 miles west of junction ST 1173. Not critical or evac (US 421 is parallel nearby) National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 374 5 Inventory Route 131010010 8 Structure Number 000000000670091 19 Bypass, Detour Length (e.g. in miles) 01 26 Functional Classification of Inventory Route 08 27 Year Built 1979 29 Average Daily Traffic 001100 49 Structure Length (e.g. in feet) 000871 52 Deck Width, Out-to-Out (e.g. in feet) 031.0 60 Substructure 7 61 Channel and Channel Protection 7 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 6% 113 Scour Critical Bridges (2002 NBI Guidelines) 3
NCHRP 24-25 Page 249 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 6 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 15,797 ft2; Cost per unit area: 100.80$/ft2; Cost Multiplier: 2.0 $3.16 million Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠365 Value of time per adult * Use Table 3 ($/hr) ⧠$6.72 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $50,000 Estimated cost of installing scour countermeasures $61,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $60,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $20,000* *have a scour report.
NCHRP 24-25 Page 250 Phase II Appendices Scour Management Evaluation 3. State Road 1001 over Yadkin River Bridge 670091 in Forsyth County, NC was constructed in 1979 and supports a rural minor collector class road. This bridgeâs foundation is known with an NBI item 113 rating of â3â (scour critical and unstable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route, and does not provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor collector class bridge, according to the guidelines, is 0.001 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 8 Rural minor collector classification NBI item 71 (bridge survey) 8 Waterway is equal to the desirable criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 7 Foundation is in good condition NBI item 61 (bridge survey) 7 Channel has some minor drift and damage â´Scour Vulnerability (guidelines) 7 Countermeasures installed make it stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.001. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (36 years, according to the survey respondent) as follows:1-(1-0.00025)36, or about 0.009 (a 1 in 111 chance of failure in the next 36 years). This and other survey data are now used to calculate the risk of death as follows: 961,8$)2()/000,500($)/009.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $50,000 and the risk of death is $8,961, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 251 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $800,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $2,840,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 152,201$ )365()/100,1()1( 100 6/30.1$ 100 61/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 605,116$ /40 )365()/100,1()1( 100 6)/01.22($ 100 61)63.1()/72.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $4,157,757. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $37,257. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. However, if this bridge had an unknown foundation the guidelines would have strongly recommended that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 252 Phase II Appendices Bridge #4 The Initial Survey Respondent Information Name Mohammed Mulla E-mail Address mmulla@dot.state.nc.us Job Title Transportation Engineer Manager Phone 919-250-4088 Job Description (In what way does your job involve bridge maintenance?) Assistant State Geotechnical Engineer Mailing Address 1589 Mail Service Center Raleigh, NC 27699 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. 330091 Forsyth County. ST 1001 across Yadkin River Not critical or evac. (appears to have parallel routes) National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 374 5 Inventory Route 131011470 8 Structure Number 000000000450113 19 Bypass, Detour Length (e.g. in miles) 01 26 Functional Classification of Inventory Route 09 27 Year Built 1959 29 Average Daily Traffic 1000 49 Structure Length (e.g. in feet) 109 52 Deck Width, Out-to-Out (e.g. in feet) 20.3 60 Substructure 6 61 Channel and Channel Protection 6 71 Waterway Adequacy 6 109 Average Daily Truck Traffic 06 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 253 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 46 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area 2213 ft2; Cost per unit area 70 $/ft2; Cost Multiplier: 1.25 $200,000 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠365 Value of time per adult * Use Table 3 ($/hr) ⧠$6.72 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $50,000 Estimated cost of installing scour countermeasures $50,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $20,000
NCHRP 24-25 Page 254 Phase II Appendices Scour Management Evaluation 4. Pearl Street over Mill River Bridge 450113 in Cleveland County, NC was constructed in 1959 and supports a rural local class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports an urban road, which is not a principal arterial or emergency route, and does not provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural local class bridge, according to the guidelines, is 0.002 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 9 Rural local classification NBI item 71 (bridge survey) 6 Waterway meets the minimum limits for no action â´Overtopping Frequency (guidelines) O Occasional (once in 3-10 years) NBI item 60 (bridge survey) 6 Foundation is in satisfactory condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.0004 A 1 in 2,500 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.002. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (46 years, according to the survey respondent) as follows:1-(1-0.0004)46, or about 0.018 (a 1 in 56 chance of failure in the next 46 years). This and other survey data are now used to calculate the risk of death as follows: 235,18$)2()/000,500($)/018.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $50,000 and the risk of death is $18,235, automated scour monitoring may not be warranted.
NCHRP 24-25 Page 255 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $50,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $200,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 865,182$ )365()/000,1()1( 100 6/30.1$ 100 61/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 005,106$ /40 )365()/000,1()1( 100 6)/01.22($ 100 61)63.1()/72.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $1,488,870. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $27,150. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures. However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 256 Phase II Appendices Bridge #5 The Initial Survey Respondent Information Name Scott Webb E-mail Address swebb@dot.state.nc.us Job Title Transportation Engineer III Phone 919-250-4088 Job Description (In what way does your job involve bridge maintenance?) Foundation Recommendations Mailing Address 1589 Mail Service Center Raleigh, NC 27699 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. 060115 Beaufort County, SR 13134 over Upper Goose Creek 1.4 miles from SR 1333 No parallel structure. Critical route National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 374 5 Inventory Route 131018340 8 Structure Number 000000000130115 19 Bypass, Detour Length (e.g. in miles) 11 26 Functional Classification of Inventory Route 9 27 Year Built 1976 29 Average Daily Traffic 320 49 Structure Length (e.g. in feet) 53 52 Deck Width, Out-to-Out (e.g. in feet) 29.4 60 Substructure 7 61 Channel and Channel Protection 7 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 6 113 Scour Critical Bridges (2002 NBI Guidelines) 8
NCHRP 24-25 Page 257 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 25 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 1550 ft2; Cost per unit area: 50 $/ft2; Cost Multiplier: 1.1 $85,000 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠730 Value of time per adult * Use Table 3 ($/hr) ⧠$6.72 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠1 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $50,000 Estimated cost of installing scour countermeasures $50,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $20,000* *have a scour report
NCHRP 24-25 Page 258 Phase II Appendices Scour Management Evaluation 5. State Road 1334 over Upper Goose Creek Bridge 130115 in Beaufort County, NC was constructed in 1976. It supports a rural local class road. This bridgeâs foundation is known with an NBI item 113 rating of â8â (analysis: stable; survey: stable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural road, which is an emergency evacuation route. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. However, this bridge has significant economic value and may provide critical access to local services. Thus, if this bridge had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 259 Phase II Appendices Bridge #6 The Initial Survey Respondent Information Name Scott Webb E-mail Address swebb@dot.state.nc.us Job Title Transportation Engineer III Phone 919-250-4088 Job Description (In what way does your job involve bridge maintenance?) Foundation Recommendations Mailing Address 1589 Mail Service Center Raleigh, NC 27699 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. 060101 Beaufort County SR 1518 over Runyon Creek No parallel structure Critical route National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 374 5 Inventory Route 1310115180 8 Structure Number 000000000120101 19 Bypass, Detour Length (e.g. in miles) 5 26 Functional Classification of Inventory Route 9 27 Year Built 1964 29 Average Daily Traffic 530 49 Structure Length (e.g. in feet) 52 52 Deck Width, Out-to-Out (e.g. in feet) 25 60 Substructure 7 61 Channel and Channel Protection 8 71 Waterway Adequacy 5 109 Average Daily Truck Traffic 6 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 260 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 15 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 1300 ft2; Cost per unit area: 50 $/ft2; Cost Multiplier: 1.25 $81,250 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠548 Value of time per adult * Use Table 3 ($/hr) ⧠$6.72 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $50,000 Estimated cost of installing scour countermeasures $50,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $20,000
NCHRP 24-25 Page 261 Phase II Appendices Scour Management Evaluation 6. State Road 1518 over Runyon Creek Bridge 120101 in Beaufort County, NC was constructed in 1964. It supports a rural local class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is an emergency evacuation route. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge provides a critical emergency evacuation route for local residents and has significant economic value. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 262 Phase II Appendices Bridge #7 The Initial Survey Respondent Information Name Scott Webb E-mail Address swebb@dot.state.nc.us Job Title Transportation Engineer III Phone 919-250-4088 Job Description (In what way does your job involve bridge maintenance?) Foundation Recommendations Mailing Address 1589 Mail Service Center Raleigh, NC 27699 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. 250042 Cumberland County SR 2030 over unnamed creek No parallel structure Critical route National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 374 5 Inventory Route 131020300 8 Structure Number 000000000510042 19 Bypass, Detour Length (e.g. in miles) 5 26 Functional Classification of Inventory Route 8 27 Year Built 1969 29 Average Daily Traffic 620 49 Structure Length (e.g. in feet) 91 52 Deck Width, Out-to-Out (e.g. in feet) 31 60 Substructure 6 61 Channel and Channel Protection 6 71 Waterway Adequacy 7 109 Average Daily Truck Traffic 6 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 263 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 17 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 2821 ft2; Cost per unit area: 70 $/ft2; Cost Multiplier: 1.25 $246,837 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠548 Value of time per adult * Use Table 3 ($/hr) ⧠$6.72 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $100,000 Estimated cost of installing scour countermeasures $100,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $50,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $50,000
NCHRP 24-25 Page 264 Phase II Appendices Scour Management Evaluation 7. State Road 2030 over an Unnamed Creek Bridge 510042 in Cumberland County, NC was constructed in 1969. It supports a rural minor collector class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is an emergency evacuation route. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge provides a critical emergency evacuation route for local residents and has significant economic value. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 265 Phase II Appendices Bridge #8 The Initial Survey Respondent Information Name Scott Webb E-mail Address swebb@dot.state.nc.us Job Title Transportation Engineer III Phone 919-250-4088 Job Description (In what way does your job involve bridge maintenance?) Foundation Recommendations Mailing Address 1589 Mail Service Center Raleigh, NC 27699 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. 440008 Henderson County ST 1314 over Boylston Creek 1 mile south of ST 1426. Not critical National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 374 5 Inventory Route 131013140 8 Structure Number 000000000890008 19 Bypass, Detour Length (e.g. in miles) 3 26 Functional Classification of Inventory Route 9 27 Year Built 1986 29 Average Daily Traffic 1300 49 Structure Length (e.g. in feet) 42 52 Deck Width, Out-to-Out (e.g. in feet) 21 60 Substructure 6 61 Channel and Channel Protection 6 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 6 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 266 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 2 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 882 ft2; Cost per unit area: 75 $/ft2; Cost Multiplier: 1.5 $99,200 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠365 Value of time per adult * Use Table 3 ($/hr) ⧠$6.72 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $50,000 Estimated cost of installing scour countermeasures $50,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $20,000
NCHRP 24-25 Page 267 Phase II Appendices Scour Management Evaluation 8. State Road 1314 over Boyleston Creek Bridge 890008 in Henderson County, NC was constructed in 1986 and supports a rural local class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route, and does not provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural local class bridge, according to the guidelines, is 0.002 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 9 Rural local classification NBI item 71 (bridge survey) 8 Waterway is equal to the desirable criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 6 Foundation is in satisfactory condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.002. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (2 years, according to the survey respondent) as follows:1-(1-0.00025)2, or about 0.0005 (a 1 in 2,000 chance of failure in the next 2 years). This and other survey data are now used to calculate the risk of death as follows: 500$)2()/000,500($)/0005.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $50,000 and the risk of death is $500, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 268 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $50,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $99,200. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 035,715$ )365()/300,1()3( 100 6/30.1$ 100 61/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 025,414$ /40 )365()/300,1()3( 100 6)/01.22($ 100 61)63.1()/72.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $2,228,260. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $1,114. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures. However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 269 Phase II Appendices Bridge #9 The Initial Survey Respondent Information Name Scott Webb E-mail Address swebb@dot.state.nc.us Job Title Transportation Engineer III Phone 919-250-4088 Job Description (In what way does your job involve bridge maintenance?) Foundation Recommendations Mailing Address 1589 Mail Service Center Raleigh, NC 27699 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. 350032 Gaston County US 321 NBL over Crowdenâs Creek 0.1 mile south of SR 2416 Dual bridges Not critical National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 374 5 Inventory Route 121003210 8 Structure Number 000000000710032 19 Bypass, Detour Length (e.g. in miles) 1 26 Functional Classification of Inventory Route 6 27 Year Built 1931 29 Average Daily Traffic 4350 49 Structure Length (e.g. in feet) 189 52 Deck Width, Out-to-Out (e.g. in feet) 23 60 Substructure 7 61 Channel and Channel Protection 7 71 Waterway Adequacy 7 109 Average Daily Truck Traffic 8 113 Scour Critical Bridges (2002 NBI Guidelines) 8
NCHRP 24-25 Page 270 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 6 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 4350 ft2; Cost per unit area: 70 $/ft2; Cost Multiplier: 1.5 $456,000 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠365 Value of time per adult * Use Table 3 ($/hr) ⧠$6.72 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $150,000 Estimated cost of installing scour countermeasures $150,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $75,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $75,000
NCHRP 24-25 Page 271 Phase II Appendices Scour Management Evaluation 9. US 321 NBC over Crosdenâs Creek Bridge 710032 in Gaston County, NC was constructed in 1931 and supports a rural minor arterial class road. This bridgeâs foundation is known with an NBI item 113 rating of â8â (analysis: stable; survey: stable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route, and does not provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor arterial class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 6 Rural minor arterial classification NBI item 71 (bridge survey) 7 Waterway is better than the minimum criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 7 Foundation is in good condition NBI item 61 (bridge survey) 7 Channel has some minor drift and damage â´Scour Vulnerability (guidelines) 7 Countermeasures installed make it stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (6 years, according to the survey respondent) as follows:1-(1-0.00025)6, or about 0.0015 (a 1 in 667 chance of failure in the next 6 years). This and other survey data are now used to calculate the risk of death as follows: 500,1$)2()/000,500($)/0015.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $50,000 and the risk of death is $1,500, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 272 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $150,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $456,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 665,412$ )183()/350,4()1( 100 8/30.1$ 100 81/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 694,235$ /40 )183()/350,4()1( 100 8)/01.22($ 100 81)63.1()/72.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $2,104,359. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $3,155. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. However, if this bridge had an unknown foundation the guidelines would have strongly recommended that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 273 Phase II Appendices Bridge #10 The Initial Survey Respondent Information Name Scott Webb E-mail Address swebb@dot.state.nc.us Job Title Transportation Engineer III Phone 919-250-4088 Job Description (In what way does your job involve bridge maintenance?) Foundation Recommendations Mailing Address 1589 Mail Service Center Raleigh, NC 27699 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. 620013 Moore County SR1102 over Aberdeen Creek 0..2 miles west of SR 1101 No parallel structure Critical structure National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 374 5 Inventory Route 131011020 8 Structure Number 000000001250013 19 Bypass, Detour Length (e.g. in miles) 6 26 Functional Classification of Inventory Route 8 27 Year Built 1941 29 Average Daily Traffic 1300 49 Structure Length (e.g. in feet) 51 52 Deck Width, Out-to-Out (e.g. in feet) 22 60 Substructure 6 61 Channel and Channel Protection 8 71 Waterway Adequacy 8 109 Average Daily Truck Traffic 6 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 274 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 15 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 1122 ft2; Cost per unit area: 60 $/ft2; Cost Multiplier: 1.5 $101,000 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠Value of time per adult * Use Table 3 ($/hr) ⧠Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $50,000 Estimated cost of installing scour countermeasures $50,000 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $20,000 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $20,000
NCHRP 24-25 Page 275 Phase II Appendices Scour Management Evaluation 10. State Road 1102 over Aberdeen Creek Bridge 1250013 in Moore County, NC was constructed in 1941. It supports a rural minor arterial class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is an emergency evacuation route. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge provides a critical emergency evacuation route for local residents and has significant economic value. Thus, the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 276 Phase II Appendices Response to Evaluations Mohammed Mulla, an assistant state geotechnical engineer, responded to the bridge evaluation as follows: I generally agree with the concept being utilized. It does help in making a decision to be able to quantify variables as opposed to just mentally ranking the variables due to perceptions of their importance. However, after reviewing the response, I felt that most of the effect of the risk analysis was in areas that would not ultimately control the decision, such as whether or not a detour route would be considered too long for local citizens, or that a fatality would be unacceptable regardless of costs. I feel this research is a step forward, but a small step.
NCHRP 24-25 Page 277 Phase II Appendices Tennessee Bridges Bridge #1 The Initial Survey Respondent Information Name Denise Glasgow E-mail Address Denise.glasgow@state.tn.us Job Title Transportation Associate Phone 615-532-2445 Job Description (In what way does your job involve bridge maintenance?) Maintenance records for bridge repair Mailing Address 505 Deaderick Suite 1200, JK Polk Building Nashville, TN 37243-0338 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Lake County, Madie Thompson Rd over Running Reelfoot Bayou. 5 span timber stringer and timber bents. 2 lanes wide National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 474 5 Inventory Route A043 8 Structure Number 480A0430001 19 Bypass, Detour Length (e.g. in miles) 4.97 mi 26 Functional Classification of Inventory Route R/Local 27 Year Built 1930 29 Average Daily Traffic 40 49 Structure Length (e.g. in feet) 93.8 ft 52 Deck Width, Out-to-Out (e.g. in feet) 21.0 ft 60 Substructure 0 61 Channel and Channel Protection 0 71 Waterway Adequacy 0 109 Average Daily Truck Traffic 2% 113 Scour Critical Bridges (2002 NBI Guidelines) 0
NCHRP 24-25 Page 278 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 70 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $457,700.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days)  1095 Value of time per adult * Use Table 3 ($/hr)  6.45 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people)  0 Cost for each life lost $500,000  * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $30,000.00 Estimated cost of installing scour countermeasures $70,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $5,000.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $8,000.00
NCHRP 24-25 Page 279 Phase II Appendices Scour Management Evaluation 1. Maidie Thompson Road over Running Reelfoot Bayou Bridge 480A0430001 in Lake County, TN is two lanes wide with five spans, timber stringers, and timber bents. Constructed in 1930, this bridge supported a rural-local class road before it failed due to scour. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Conclusion This bridge could not be properly evaluated because the NBI codes provided do not reveal any information about the condition of the bridge before it failed.
NCHRP 24-25 Page 280 Phase II Appendices Bridge #2 The Initial Survey Respondent Information Name Denise Glasgow E-mail Address Denise.glasgow@state.tn.us Job Title Transportation Associate Phone 615-532-2445 Job Description (In what way does your job involve bridge maintenance?) Maintenance records for bridge repair Mailing Address 505 Deaderick Suite 1200, JK Polk Building Nashville, TN 37243-0338 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Bledsoe County; Bedwell Rd over Cove Branch. Single span 1 lane, steel I beams with steel grating deck and stacked precast concrete block abutments. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 474 5 Inventory Route A136 8 Structure Number 040A1360001 19 Bypass, Detour Length (e.g. in miles) 123.65 mi 26 Functional Classification of Inventory Route R/Local 27 Year Built 1976 29 Average Daily Traffic 30 49 Structure Length (e.g. in feet) 32.2 ft 52 Deck Width, Out-to-Out (e.g. in feet) 13.5 ft 60 Substructure 6 61 Channel and Channel Protection 6 71 Waterway Adequacy 4 109 Average Daily Truck Traffic 2% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 281 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 30 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $223,000.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days)  1095 Value of time per adult * Use Table 3 ($/hr)  $6.45 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people)  0 Cost for each life lost $500,000  * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $25,000.00 Estimated cost of installing scour countermeasures $40,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $2,500.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $8,000.00
NCHRP 24-25 Page 282 Phase II Appendices Scour Management Evaluation 2. Bedwell Road over Cove Branch Bridge 040A1360001 in Bledsoe County, TN has one span and one lane with steel I- beams and grating deck, and is supported by stacked pre-cast concrete block abutments. Constructed in 1976, this bridge supports a rural-local class road but has an unknown foundation depth. It is further assumed that foundation records can not be found because NBI item 113 is coded âUâ. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural-local class bridge, according to the guidelines, is 0.002 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 9 Rural local classification NBI item 71 (bridge survey) 4 Waterway meets minimum criteria â´Overtopping Frequency (guidelines) O Occasional (once in 3-10 years) NBI item 60 (bridge survey) 6 Foundation is in satisfactory condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.0004 A 1 in 2,500 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.002. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (30 years, according to the survey respondent) as follows:1-(1-0.0004)30, or about 0.012 (a 1 in 83 chance of failure in the next 30 years). This and other survey data are now used to calculate the risk of death as follows: 0$)0()/000,500($)012.0()0.1( 6 =â â â = â â â = peopleperson XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $25,000 and the risk of death is $0, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 283 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $40,000. The first step is to calculate the potential cost of bridge failure. The survey respondent estimated that a new bridge would cost about $223,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 141,896,1$ )1095()/30()65.123( 100 2/30.1$ 100 21/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 528,090,1$ /40 )1095()/30()65.123( 100 2)/01.22($ 100 21)63.1()/45.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages Given that the chance death is negligible, the total cost of bridge failure totals $3,209,669. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $38,293. Thus, scour countermeasures may not be warranted because the lifetime risk of failure is slightly less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures. However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 284 Phase II Appendices Bridge #3 The Initial Survey Respondent Information Name Denise Glasgow E-mail Address Denise.glasgow@state.tn.us Job Title Transportation Associate Phone 615-532-2445 Job Description (In what way does your job involve bridge maintenance?) Maintenance records for bridge repair Mailing Address 505 Deaderick Suite 1200, JK Polk Building Nashville, TN 37243-0338 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Carroll County. State Rt. 77 over Branch. 3 span precast concrete channel slab with timber bents and abutments. 2 lanes wide. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 474 5 Inventory Route SR077 8 Structure Number 09ST0770025 19 Bypass, Detour Length (e.g. in miles) 49.7 mi 26 Functional Classification of Inventory Route R/Maj Col 27 Year Built 1990 29 Average Daily Traffic 850 49 Structure Length (e.g. in feet) 50.10 ft 52 Deck Width, Out-to-Out (e.g. in feet) 28.10 ft 60 Substructure 6 61 Channel and Channel Protection 6 71 Waterway Adequacy 7 109 Average Daily Truck Traffic 3% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 285 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 25 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $285,000.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days)  548 Value of time per adult * Use Table 3 ($/hr)  $6.45 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people)  2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $30,000.00 Estimated cost of installing scour countermeasures $70,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $2,500.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $8,000.00
NCHRP 24-25 Page 286 Phase II Appendices Scour Management Evaluation 3. State Route 77 over Branch Bridge 09SR0770025 in Carroll County, TN has three spans and two lanes with timber bents and abutments and a pre-cast concrete channel slab. Constructed in 1990, this bridge supports a rural major collector class road but has an unknown foundation depth. It is further assumed that foundation records can not be found because NBI item 113 is coded âUâ. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural major collector class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 7 Rural major collector classification NBI item 71 (bridge survey) 7 Waterway exceeds than the minimum criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 6 Foundation is in satisfactory condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (25 years, according to the survey respondent) as follows:1-(1-0.00025)25, or about 0.0062 (a 1 in 161 chance of failure in the next 25 years). This and other survey data are now used to calculate the risk of death as follows: 231,6$)2()/000,500($)/0062.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $30,000 and the risk of death is $6,231, automated scour monitoring may not be warranted.
NCHRP 24-25 Page 287 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $70,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $285,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 949,007,11$ )548()/850()7.49( 100 3/30.1$ 100 31/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 367,284,6$ /40 )548()/850()7.49( 100 3)/01.22($ 100 31)63.1()/45.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $18,577,315. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $115,760. Thus, scour countermeasures are probably warranted because the lifetime risk of failure is greater than the estimated cost of scour countermeasures. Is foundation reconnaissance and scour analysis warranted? The survey respondent estimated the foundation reconnaissance and scour analysis costs to be about $2,500 and $8,000, respectively. Since this is about 15% of the estimated cost of installing countermeasures, foundation reconnaissance and scour analysis is probably warranted before installing the countermeasures. Recommended management strategy Given the discussion above the guidelines recommend the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, you could drill through the footing to determine elevation of the footing bottom. The parallel seismic test is generally the most effective NDT method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth using local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In
NCHRP 24-25 Page 288 Phase II Appendices other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 289 Phase II Appendices Bridge #4 The Initial Survey Respondent Information Name Denise Glasgow E-mail Address Denise.glasgow@state.tn.us Job Title Transportation Associate Phone 615-532-2445 Job Description (In what way does your job involve bridge maintenance?) Maintenance records for bridge repair Mailing Address 505 Deaderick Suite 1200, JK Polk Building Nashville, TN 37243-0338 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Chester County State Rt. 225 over Melton Branch. Single span precast concrete channel slab with timber abutments. 2 lanes. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 474 5 Inventory Route SR225 8 Structure Number 125R2250005 19 Bypass, Detour Length (e.g. in miles) 4.97 mi 26 Functional Classification of Inventory Route R/Maj Col 27 Year Built 1985 29 Average Daily Traffic 1300 49 Structure Length (e.g. in feet) 28.3 ft 52 Deck Width, Out-to-Out (e.g. in feet) 28.7 ft 60 Substructure 7 61 Channel and Channel Protection 6 71 Waterway Adequacy 7 109 Average Daily Truck Traffic 1% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 290 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 20 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $271,000.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠365 Value of time per adult * Use Table 3 ($/hr)  6.45 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people)  2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $25,000.00 Estimated cost of installing scour countermeasures $40,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $2,500.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $8,000.00
NCHRP 24-25 Page 291 Phase II Appendices Scour Management Evaluation 4. State Route 225 over Melton Branch Bridge 12SR2250005 in Chester County, TN has one span and two lanes with timber abutments and a pre-cast concrete channel slab. Constructed in 1985, this bridge supports a rural major collector class road but has an unknown foundation depth. It is further assumed that foundation records can not be found because NBI item 113 is coded âUâ. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural major collector class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 7 Rural major collector classification NBI item 71 (bridge survey) 7 Waterway exceeds the minimum criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 7 Foundation is in good condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (20 years, according to the survey respondent) as follows:1-(1-0.00025)20, or about 0.005 (a 1 in 200 chance of failure in the next 20 years). This and other survey data are now used to calculate the risk of death as follows: 988,4$)2()/000,500($)/005.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $25,000 and the risk of death is $4,988, automated scour monitoring may not be warranted.
NCHRP 24-25 Page 292 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $40,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $271,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 265,081,1$ )365()/300,1()97.4( 100 1/30.1$ 100 11/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 618,626$ /40 )365()/300,1()97.4( 100 1)/01.22($ 100 11)63.1()/45.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $2,978,883. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $14,859. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures. However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 293 Phase II Appendices Bridge #5 The Initial Survey Respondent Information Name Denise Glasgow E-mail Address Denise.glasgow@state.tn.us Job Title Transportation Associate Phone 615-532-2445 Job Description (In what way does your job involve bridge maintenance?) Maintenance records for bridge repair Mailing Address 505 Deaderick Suite 1200, JK Polk Building Nashville, TN 37243-0338 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Davidson County, Coopertown Road over Long Creek. 2 lane, single span, prestressed precast concrete box beams. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 474 5 Inventory Route A989 8 Structure Number 19019430001 19 Bypass, Detour Length (e.g. in miles) 9.94 mi 26 Functional Classification of Inventory Route U/Local 27 Year Built 1960 29 Average Daily Traffic 1700 49 Structure Length (e.g. in feet) 53.2 ft 52 Deck Width, Out-to-Out (e.g. in feet) 23.11 ft 60 Substructure 7 61 Channel and Channel Protection 7 71 Waterway Adequacy 7 109 Average Daily Truck Traffic 1 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 294 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 30 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $127,000.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days)  365 Value of time per adult * Use Table 3 ($/hr)  6.45 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people)  2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $25,000.00 Estimated cost of installing scour countermeasures $40,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $2,500.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $8,000.00
NCHRP 24-25 Page 295 Phase II Appendices Scour Management Evaluation 5. Coopertown Road over Long Creek Bridge 19019430001 in Davidson County, TN has one span and two lanes with pre- stressed pre-cast concrete box beams. Constructed in 1960, this bridge supports an urban- local class road but has an unknown foundation depth. It is further assumed that foundation records can not be found because NBI item 113 is coded âUâ. Is it a high-priority bridge? This bridge supports an urban road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for an urban-local class bridge, according to the guidelines, is 0.002 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 19 Urban local classification NBI item 71 (bridge survey) 7 Waterway exceeds the minimum criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 7 Foundation is in good condition NBI item 61 (bridge survey) 7 Channel has some minor drift and damage â´Scour Vulnerability (guidelines) 7 Countermeasures were installed and is now stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.002. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (30 years, according to the survey respondent) as follows:1-(1-0.00025)30, or about 0.0075 (a 1 in 133 chance of failure in the next 30 years). This and other survey data are now used to calculate the risk of death as follows: 473,7$)2()/000,500($)0075.0()0.1( 6 =â â â = â â â = peopleperson XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $25,000 and the risk of death is $7,473, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 296 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $40,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $127,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 923,827,2$ )365()/1700()94.9( 100 1/30.1$ 100 11/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 848,638,1$ /40 )365()/1700()94.9( 100 1)/01.22($ 100 11)63.1()/45.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $5,593,771. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $41,802. Thus, scour countermeasures are probably warranted because the lifetime risk of failure is greater than the estimated cost of scour countermeasures. Is foundation reconnaissance and scour analysis warranted? The survey respondent estimated the foundation reconnaissance and scour analysis costs to be about $2,500 and $8,000, respectively. Since this is only about 26% of the estimated cost of installing countermeasures, foundation reconnaissance and scour analysis are probably warranted before installing the countermeasures. Recommended management strategy Given the results explained above, the guidelines recommend the following steps to ensure the safety of the bridge: 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, you could drill through the footing to determine elevation of the footing bottom. The parallel seismic test is generally the most effective NDT method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth using local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In
NCHRP 24-25 Page 297 Phase II Appendices other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 298 Phase II Appendices Bridge #6 The Initial Survey Respondent Information Name Denise Glasgow E-mail Address Denise.glasgow@state.tn.us Job Title Transportation Associate Phone 615-532-2445 Job Description (In what way does your job involve bridge maintenance?) Maintenance records for bridge repair Mailing Address 505 Deaderick Suite 1200, JK Polk Building Nashville, TN 37243-0338 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Grundy County. Bells Mill Road over Caldwell Creek. 2 lane, single span, steel I-beam. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 474 5 Inventory Route 2132 8 Structure Number 31021320001 19 Bypass, Detour Length (e.g. in miles) 6.83 mi 26 Functional Classification of Inventory Route R/Min Col 27 Year Built 1940 29 Average Daily Traffic 220 49 Structure Length (e.g. in feet) 54.2 ft 52 Deck Width, Out-to-Out (e.g. in feet) 22.8 ft 60 Substructure 5 61 Channel and Channel Protection 5 71 Waterway Adequacy 6 109 Average Daily Truck Traffic 5 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 299 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 5 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $355,000.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days)  730 Value of time per adult * Use Table 3 ($/hr)  6.45 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour v Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people)  1 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $25,000.00 Estimated cost of installing scour countermeasures $40,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $2,500.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $8,000.00
NCHRP 24-25 Page 300 Phase II Appendices Scour Management Evaluation 6. Bells Mill Road over Caldwell Creek Bridge 31021320001 in Grundy County, TN has one span and two lanes with steel I- beams. Constructed in 1930, this bridge supports a rural minor collector class road but has an unknown foundation depth. It is further assumed that foundation records can not be found because NBI item 113 is coded âUâ. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor collector class bridge, according to the guidelines, is 0.001 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 8 Rural local classification NBI item 71 (bridge survey) 6 Waterway exceeds the minimum criteria â´Overtopping Frequency (guidelines) O Occasional (once in 3-10 years) NBI item 60 (bridge survey) 5 Foundation is in fair condition NBI item 61 (bridge survey) 5 Channel banks are eroding; major damage â´Scour Vulnerability (guidelines) 5 Analysis: stable; Survey: scour is within limits â´Annual probability of failure (guidelines) 0.00004 A 1 in 25,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.001. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (5 years, according to the survey respondent) as follows:1-(1-0.00004)5, or about 0.0002 (a 1 in 5,000 chance of failure in the next 5 years). This and other survey data are now used to calculate the risk of death as follows: 100$)1()/000,500($)0002.0()0.1( 6 =â â â = â â â = personperson XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $25,000 and the risk of death is $100, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 301 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $40,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $355,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 222,540$ )730()/220()83.6( 100 5/30.1$ 100 51/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 069,304$ /40 )730()/220()83.6( 100 5)/01.22($ 100 51)63.1()/45.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $1,699,291. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $340. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures. However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 302 Phase II Appendices Bridge #7 The Initial Survey Respondent Information Name Denise Glasgow E-mail Address Denise.glasgow@state.tn.us Job Title Transportation Associate Phone 615-532-2445 Job Description (In what way does your job involve bridge maintenance?) Maintenance records for bridge repair Mailing Address 505 Deaderick Suite 1200, JK Polk Building Nashville, TN 37243-0338 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Marion County. Valley View Highway over Owen Spring Creek. 2 lane, 4 span concrete deck girder. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 474 5 Inventory Route 1131 8 Structure Number 58SR0270007 19 Bypass, Detour Length (e.g. in miles) 8.07 mi 26 Functional Classification of Inventory Route R/Min Col 27 Year Built 1939 29 Average Daily Traffic 2340 49 Structure Length (e.g. in feet) 113.10 ft 52 Deck Width, Out-to-Out (e.g. in feet) 36.5 ft 60 Substructure 6 61 Channel and Channel Protection 7 71 Waterway Adequacy 7 109 Average Daily Truck Traffic 26% 113 Scour Critical Bridges (2002 NBI Guidelines) 5
NCHRP 24-25 Page 303 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 10 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $973,000.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days)  365 Value of time per adult * Use Table 3 ($/hr)  6.45 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people)  2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $30,000 Estimated cost of installing scour countermeasures $80,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $5,000.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $8,000.00
NCHRP 24-25 Page 304 Phase II Appendices Scour Management Evaluation 7. Valley View Highway over Owen Spring Creek Bridge 58SR0270007 in Marion County, TN has four spans and two lanes with concrete deck girders. Constructed in 1939, this bridge supports a rural minor collector class road, and has a known foundation with an NBI item 113 rating of â5â (Analysis: stable; Survey: within limits). However, this bridge will be evaluated as if it were unknown. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor collector class bridge, according to the guidelines, is 0.001 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 8 Rural local classification NBI item 71 (bridge survey) 7 Waterway exceeds the minimum criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 6 Foundation is in satisfactory condition NBI item 61 (bridge survey) 7 Channel has some minor drift and damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.001. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (10 years, according to the survey respondent) as follows:1-(1-0.00025)10, or about 0.0025 (a 1 in 400 chance of failure in the next 10 years). This and other survey data are now used to calculate the risk of death as follows: 497,2$)2()/000,500($)0025.0()0.1( 6 =â â â = â â â = peopleperson XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $30,000 and the risk of death is $2,497, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 305 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $80,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $973,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 926,624,4$ )365()/340,2()07.8( 100 26/30.1$ 100 261/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 694,326,2$ /40 )365()/340,2()07.8( 100 26)/01.22($ 100 261)63.1()/45.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $8,924,620. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $22,286. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. However, if the foundation was unknown, the guidelines would have strongly recommended that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 306 Phase II Appendices Bridge #8 The Initial Survey Respondent Information Name Denise Glasgow E-mail Address Denise.glasgow@state.tn.us Job Title Transportation Associate Phone 615-532-2445 Job Description (In what way does your job involve bridge maintenance?) Maintenance records for bridge repair Mailing Address 505 Deaderick Suite 1200, JK Polk Building Nashville, TN 37243-0338 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Cumberland City. State Rt. 233 over Wells Creek. 2 lane, 6 span prestressed precast concrete box beams. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 474 5 Inventory Route SR233 8 Structure Number 81561140007 19 Bypass, Detour Length (e.g. in miles) 4.97 mi 26 Functional Classification of Inventory Route R/Maj Col 27 Year Built 1961 29 Average Daily Traffic 2950 49 Structure Length (e.g. in feet) 202.1 ft 52 Deck Width, Out-to-Out (e.g. in feet) 34.5 ft 60 Substructure 6 61 Channel and Channel Protection 7 71 Waterway Adequacy 6 109 Average Daily Truck Traffic 4% 113 Scour Critical Bridges (2002 NBI Guidelines) 5
NCHRP 24-25 Page 307 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 30 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $172,000.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days)  365 Value of time per adult * Use Table 3 ($/hr)  6.45 Average car occupancy rate 1.63 people  Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people)  2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $30,000.00 Estimated cost of installing scour countermeasures $80,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $5,000.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $8,000.00
NCHRP 24-25 Page 308 Phase II Appendices Scour Management Evaluation 8. State Route 233 over Wells Creek Bridge 81S61140007 in Stewart County, TN has six spans and two lanes with pre- stressed pre-cast concrete box beams. Constructed in 1961, this bridge supports a rural major collector class roadway, and has a known foundation with an NBI item 113 rating of â5â (Analysis: stable; Survey: within limits). However, this bridge will be evaluated as if it were unknown. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural major collector class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 7 Rural major collector classification NBI item 71 (bridge survey) 4 Waterway meets the minimum limits for no action â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 6 Foundation is in satisfactory condition NBI item 61 (bridge survey) 7 Channel has some minor drift and damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (30 years, according to the survey respondent) as follows:1-(1-0.00025)30, or about 0.0075 (a 1 in 133 chance of failure in the next 30 years). This and other survey data are now used to calculate the risk of death as follows: 473,7$)2()/000,500($)0075.0()0.1( 6 =â â â = â â â = peopleperson XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $30,000 and the risk of death is $7,473, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 309 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $80,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $172,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 101,590,2$ )365()/950,2()97.4( 100 4/30.1$ 100 41/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 084,468,1$ /40 )365()/950,2()97.4( 100 4)/01.22($ 100 41)63.1()/45.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $5,230,185. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $39,085. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge has a known foundation, and thus does not require any additional action. However, if the foundation was unknown, the guidelines would have strongly recommended that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 310 Phase II Appendices Bridge #9 The Initial Survey Respondent Information Name Denise Glasgow E-mail Address Denise.glasgow@state.tn.us Job Title Transportation Associate Phone 615-532-2445 Job Description (In what way does your job involve bridge maintenance?) Maintenance records for bridge repair Mailing Address 505 Deaderick Suite 1200, JK Polk Building Nashville, TN 37243-0338 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Warren County, Old Shelbyville Road over Oakland Branch. 2 lane, single span, steel I-beam bridge. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 474 5 Inventory Route 1114 8 Structure Number 89542900017 19 Bypass, Detour Length (e.g. in miles) 4.97 mi 26 Functional Classification of Inventory Route R/Min Col 27 Year Built 1930 29 Average Daily Traffic 670 49 Structure Length (e.g. in feet) 29.10 ft 52 Deck Width, Out-to-Out (e.g. in feet) 21.0 ft 60 Substructure 5 61 Channel and Channel Protection 5 71 Waterway Adequacy 6 109 Average Daily Truck Traffic 10% 113 Scour Critical Bridges (2002 NBI Guidelines) 3
NCHRP 24-25 Page 311 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 5 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $253,000.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days)  548 Value of time per adult * Use Table 3 ($/hr)  6.45 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people)  2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $30,000.00 Estimated cost of installing scour countermeasures $40,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $2,500.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $8,000.00
NCHRP 24-25 Page 312 Phase II Appendices Scour Management Evaluation 9. Old Shelbyville Road over Oakland Branch Bridge 89S42900017 in Warren County, TN has one span and two lanes with steel I- beams. Constructed in 1930, this bridge supports a rural minor collector class roadway, and has a known foundation with an NBI item 113 rating of â3â (Scour critical and unstable). However, this bridge will be evaluated as if it were unknown. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural major collector class bridge, according to the guidelines, is 0.001 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 8 Rural minor collector classification NBI item 71 (bridge survey) 6 Waterway is equal to the minimum criteria â´Overtopping Frequency (guidelines) O Occasional (once in 3-10 years) NBI item 60 (bridge survey) 5 Foundation is in fair condition NBI item 61 (bridge survey) 5 Channel banks are eroding; major damage â´Scour Vulnerability (guidelines) 5 Analysis: stable; Survey: scour is within limits â´Annual probability of failure (guidelines) 0.00004 A 1 in 25,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.001. However, because the foundation has been assumed to be unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (5 years, according to the survey respondent) as follows:1-(1-0.00004)5, or about 0.0002 (a 1 in 5,000 chance of failure in the next 5 years). This and other survey data are now used to calculate the risk of death as follows: 200$)2()/000,500($)0002.0()0.1( 6 =â â â = â â â = peopleperson XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $30,000 and the risk of death is $200, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 313 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $40,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $253,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 260,976$ )548()/670()97.4( 100 10/30.1$ 100 101/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 069,532$ /40 )548()/670()97.4( 100 10)/01.22($ 100 101)63.1()/45.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $2,761,329. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $552. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge has a known foundation, and requires action. However, if the foundation was unknown, the guidelines would have strongly recommended that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 314 Phase II Appendices Bridge #10 The Initial Survey Respondent Information Name Denise Glasgow E-mail Address Denise.glasgow@state.tn.us Job Title Transportation Associate Phone 615-532-2445 Job Description (In what way does your job involve bridge maintenance?) Maintenance records for bridge repair Mailing Address 505 Deaderick Suite 1200, JK Polk Building Nashville, TN 37243-0338 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Sevier County, Railroad Street over Middle Creek. 2 lane, 2 span, steel I-beam. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 474 5 Inventory Route B072 8 Structure Number 780B0720001 19 Bypass, Detour Length (e.g. in miles) 1.86 mi 26 Functional Classification of Inventory Route U/Local 27 Year Built 1940 29 Average Daily Traffic 960 49 Structure Length (e.g. in feet) 48.11 ft 52 Deck Width, Out-to-Out (e.g. in feet) 25.7 ft 60 Substructure 5 61 Channel and Channel Protection 6 71 Waterway Adequacy 7 109 Average Daily Truck Traffic 2% 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 315 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 10 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $373,000.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠548 Value of time per adult * Use Table 3 ($/hr)  6.45 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people)  2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $30,000.00 Estimated cost of installing scour countermeasures $50,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $2,500.00 Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $8,000.00
NCHRP 24-25 Page 316 Phase II Appendices Scour Management Evaluation 10. Railroad Street over Middle Creek Bridge 780B0720001 in Sevier County, TN has two spans and two lanes with steel I- beams. Constructed in 1940, this bridge supports an urban-local class road but has an unknown foundation depth. It is further assumed that foundation records can not be found because NBI item 113 is coded âUâ. Is it a high-priority bridge? This bridge supports an urban road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for an urban-local class bridge, according to the guidelines, is 0.002 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 19 Rural local classification NBI item 71 (bridge survey) 7 Waterway exceeds the minimum criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 5 Foundation is in fair condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 5 Analysis: stable; Survey: scour is within limits â´Annual probability of failure (guidelines) 0.000008 A 1 in 125,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.002. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (10 years, according to the survey respondent) as follows:1-(1-0.000008)10, or about 0.00008 (a 1 in 12,500 chance of failure in the next 10 years). This and other survey data are now used to calculate the risk of death as follows: 80$)2()/000,500($)00008.0()0.1( 6 =â â â = â â â = peopleperson XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $30,000 and the risk of death is $80, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 317 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $50,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $373,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 964,456$ )548()/960()86.1( 100 2/30.1$ 100 21/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 814,262$ /40 )548()/960()86.1( 100 2)/01.22($ 100 21)63.1()/45.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $2,092,777. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $167. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures. However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 318 Phase II Appendices Response to Evaluations Wayne Seger, a Civil engineering manager II, was not able to finish his response to the bridge evaluations. However, the following is his preliminary comments. I've read through your assessments of the bridge information sent and find it interesting and somewhat thinking of voodoo magic. I didn't really follow, in this first read through, where all of the numbers originated but Iâll comb back through it to see if I can make better sense of logic. If you don't mind, Iâll share this with my boss for his opinion and thoughts. I think he'll have it done fairly quickly. I'll let you know what he says about it. The overall approach, in my preliminary opinion, is that it has a good thought path and guide. I just want to digest it a bit before passing final judgment.
NCHRP 24-25 Page 319 Phase II Appendices Texas Bridges Bridge #1 The Initial Survey Respondent Information Name Alan Kowalik E-mail Address akowali@dot.state.tx.us Job Title Bridge Inspection Supervisor Phone 512-416-2208 Job Description (In what way does your job involve bridge maintenance?) Supervise the bridge inspection program and the NBI Database Mailing Address 125 East 11th Street Austin, TX 78701 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. FM 56 over Bosque River â 16-span bridge with continuous steel I-beams. Maximum span length is 75 ft on a concrete spread footing. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 486 5 Inventory Route 1-15-1-0056-0 8 Structure Number 090180039801026 19 Bypass, Detour Length (e.g. in miles) 20 26 Functional Classification of Inventory Route 07 27 Year Built 1950 29 Average Daily Traffic 2300 49 Structure Length (e.g. in feet) 535 52 Deck Width, Out-to-Out (e.g. in feet) 29.2 60 Substructure 4 61 Channel and Channel Protection 4 71 Waterway Adequacy 6 109 Average Daily Truck Traffic 13 113 Scour Critical Bridges (2002 NBI Guidelines) 3
NCHRP 24-25 Page 320 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 20 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 15,622 ft2; Cost per unit area: 46 $/ft2; Cost Multiplier: 1.5 $1,077,918.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠365 Value of time per adult * Use Table 3 ($/hr) ⧠$6.96 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $ No information Estimated cost of installing scour countermeasures $ No information Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $ N/A â depth known Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000.00
NCHRP 24-25 Page 321 Phase II Appendices Scour Management Evaluation 1. FM 56 over Bosque River Bridge 090180039801026 in Bosque County, TX was constructed in 1950 and supports a rural major collector class road. This bridgeâs foundation is known with an NBI item 113 rating of â3â (scour critical and unstable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency evacuation route, and does not provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor arterial class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 7 Rural major collector classification NBI item 71 (bridge survey) 6 Waterway meets the minimum criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 4 Foundation is in poor condition NBI item 61 (bridge survey) 4 Channel protection/banks have severe damage â´Scour Vulnerability (guidelines) 4 Analysis: stable; Survey: foundation is exposed â´Annual probability of failure (guidelines) 0.0005 A 1 in 2,000 chance of failure in any given year This bridge does not meet the minimum performance level because the annual probability of failure is not less than 0.0005. Recommended management strategy This bridge has a known foundation, and requires action. Furthermore, this bridge does not meet the minimum performance level for bridges with unknown foundations. Thus, if this bridge had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be
NCHRP 24-25 Page 322 Phase II Appendices necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 323 Phase II Appendices Bridge #2 The Initial Survey Respondent Information Name Alan Kowalik E-mail Address akowali@dot.state.tx.us Job Title Bridge Inspection Supervisor Phone 512-416-2208 Job Description (In what way does your job involve bridge maintenance?) Supervise the bridge inspection program and the NBI Database Mailing Address 125 East 11th Street Austin, TX 78701 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. SH over Fish Creek â 5-span-concrete T-beams. 5 â 29 ft simple spans on multiple concrete piles. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 486 5 Inventory Route 1-13-1-0006-0 8 Structure Number 090740004904052 19 Bypass, Detour Length (e.g. in miles) 6 26 Functional Classification of Inventory Route 02 27 Year Built 1934 29 Average Daily Traffic 7600 49 Structure Length (e.g. in feet) 143 52 Deck Width, Out-to-Out (e.g. in feet) 45.3 60 Substructure 7 61 Channel and Channel Protection 7 71 Waterway Adequacy 6 109 Average Daily Truck Traffic 26 113 Scour Critical Bridges (2002 NBI Guidelines) 3
NCHRP 24-25 Page 324 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 4 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 6,478 ft2; Cost per unit area: 65 $/ft2; Cost Multiplier: 2.0 $842,140.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠183 Value of time per adult * Use Table 3 ($/hr)  6.96 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people)  5 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $ No information Estimated cost of installing scour countermeasures $50,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $ N/A â depth known Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000.00
NCHRP 24-25 Page 325 Phase II Appendices Scour Management Evaluation 2. State Highway 6 over Fish Creek Bridge 090740004904052 in Falls County, TX was constructed in 1934 and reconstructed in 1958 and supports a rural principal arterial class road. This bridgeâs foundation is known with an NBI item 113 rating of â3â (scour critical and unstable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural principal arterial and thus has significant economic value and may provide critical access to local services. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has a known foundation, and requires action. Furthermore, this bridge has significant economic value and provides critical access to local services. Thus, if this bridge had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 326 Phase II Appendices Bridge #3 The Initial Survey Respondent Information Name Alan Kowalik E-mail Address akowali@dot.state.tx.us Job Title Bridge Inspection Supervisor Phone 512-416-2208 Job Description (In what way does your job involve bridge maintenance?) Supervise the bridge inspection program and the NBI Database Mailing Address 125 East 11th Street Austin, TX 78701 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. IH 35W south-bound at Island Creek â 5 simple span â pan girder (concrete) type bridge on multiple concrete drilled shafts. 4 shafts per bent line founded on shale. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 486 5 Inventory Route 1-11-1-0035-4 8 Structure Number 091100001423285 19 Bypass, Detour Length (e.g. in miles) 6 26 Functional Classification of Inventory Route 01 27 Year Built 1965 29 Average Daily Traffic 13,000 49 Structure Length (e.g. in feet) 209 52 Deck Width, Out-to-Out (e.g. in feet) 41.7 60 Substructure 6 61 Channel and Channel Protection 6 71 Waterway Adequacy 6 109 Average Daily Truck Traffic 25 113 Scour Critical Bridges (2002 NBI Guidelines) 3
NCHRP 24-25 Page 327 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 35 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 8715 ft2; Cost per unit area: 60 $/ft2; Cost Multiplier: 2.0 $1,045,800 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠183 Value of time per adult * Use Table 3 ($/hr) ⧠6.96 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people)  3 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $No information Estimated cost of installing scour countermeasures $50,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $N/A â depth known Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000.00
NCHRP 24-25 Page 328 Phase II Appendices Scour Management Evaluation 3. I-35W SB over Island Creek Bridge 091100001423285 in Hill County, TX was constructed in 1965 and supports a rural interstate. This bridgeâs foundation is known with an NBI item 113 rating of â3â (scour critical and unstable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural principal arterial and thus has significant economic value and may provide critical access to local services. Thus, in this context this bridge is considered a high priority bridge and should be given special attention. Recommended management strategy This bridge has a known foundation, and requires action. Furthermore, this bridge has significant economic value and provides critical access to local services. Thus, if this bridge had an unknown foundation the guidelines would have recommended the following three-step strategy to ensure the safety of this bridge. 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, drill through the footing to determine elevation of the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles. The parallel seismic test is generally the most effective reconnaissance method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth. For piles, assume a 10 foot depth or use local knowledge. This should be a conservative assumption. Spread footing depths are easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 329 Phase II Appendices Bridge #4 The Initial Survey Respondent Information Name Alan Kowalik E-mail Address akowali@dot.state.tx.us Job Title Bridge Inspection Supervisor Phone 512-416-2208 Job Description (In what way does your job involve bridge maintenance?) Supervise the bridge inspection program and the NBI Database Mailing Address 125 East 11th Street Austin, TX 78701 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. SH 171 at Ash Creek â 40 simple concrete flat slabs on multiple concrete piling. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 486 5 Inventory Route 1-13-1-0171-0 8 Structure Number 091100041802028 19 Bypass, Detour Length (e.g. in miles) 13 26 Functional Classification of Inventory Route 07 27 Year Built 1940 29 Average Daily Traffic 2800 49 Structure Length (e.g. in feet) 800 52 Deck Width, Out-to-Out (e.g. in feet) 35.3 60 Substructure 5 61 Channel and Channel Protection 5 71 Waterway Adequacy 6 109 Average Daily Truck Traffic 22 113 Scour Critical Bridges (2002 NBI Guidelines) 3
NCHRP 24-25 Page 330 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 9 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 28,240 ft2; Cost per unit area: 67 $/ft2; Cost Multiplier: 1.5 $2,838,120.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠365 Value of time per adult * Use Table 3 ($/hr) ⧠6.96 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $ No information Estimated cost of installing scour countermeasures $ No information Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $N/A - depth known Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000.00
NCHRP 24-25 Page 331 Phase II Appendices Scour Management Evaluation 4. State Highway 171 over Ash Creek Bridge 091100041802028 in Hill County, TX was constructed in 1940 and reconstructed in 1966 and supports a rural major collector class road. This bridgeâs foundation is known with an NBI item 113 rating of â3â (scour critical and unstable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural major collector class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 7 Rural major collector classification NBI item 71 (bridge survey) 6 Waterway meets the minimum criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 5 Foundation is in fair condition NBI item 61 (bridge survey) 5 Channel banks are eroding; major damage â´Scour Vulnerability (guidelines) 5 Analysis: stable; Survey: scour is within limits â´Annual probability of failure (guidelines) 0.00008 A 1 in 125,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is assumed to be unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (9 years, according to the survey respondent) as follows:1-(1-0.00008)9, or about 0.000072 (a 1 in 13,889 chance of failure in the next 9 years). This and other survey data are now used to calculate the risk of death as follows: 72$)2()/000,500($)000072.0()0.1( 6 =â â â = â â â = peopleperson XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $20,000 and the risk of death is $72, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 332 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which we estimated to be about $50,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $2,838,000. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 182,463,8$ )365()/800,2()13( 100 22/30.1$ 100 221/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 513,547,4$ /40 )365()/800,2()13( 100 22)/01.22($ 100 221)63.1()/96.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $16,848,815. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $1,213. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge has a known foundation, and requires action. If this bridge had an unknown foundation, it would have met the performance standards for these guidelines would not have warranted automated scour monitoring or countermeasures. The guidelines would have strongly recommended that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 333 Phase II Appendices Bridge #5 The Initial Survey Respondent Information Name Alan Kowalik E-mail Address akowali@dot.state.tx.us Job Title Bridge Inspection Supervisor Phone 512-416-2208 Job Description (In what way does your job involve bridge maintenance?) Supervise the bridge inspection program and the NBI Database Mailing Address 125 East 11th Street Austin, TX 78701 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. FM 34 at Sanders Creek â 6 simple spans prestressed concrete box girders on multiple concrete drilled shafts National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 486 5 Inventory Route 1-15-1-0039-0 8 Structure Number 091470064302038 19 Bypass, Detour Length (e.g. in miles) 11 26 Functional Classification of Inventory Route 07 27 Year Built 1977 29 Average Daily Traffic 2700 49 Structure Length (e.g. in feet) 316 52 Deck Width, Out-to-Out (e.g. in feet) 36.6 60 Substructure 7 61 Channel and Channel Protection 7 71 Waterway Adequacy 6 109 Average Daily Truck Traffic 10 113 Scour Critical Bridges (2002 NBI Guidelines) 3
NCHRP 24-25 Page 334 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 11,566 ft2; Cost per unit area: 63 $/ft2; Cost Multiplier: 1.5 $1,092,987.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠365 Value of time per adult * Use Table 3 ($/hr) ⧠6.96 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠2 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $No information Estimated cost of installing scour countermeasures $50,000.00 Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $ N/A - depth known Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $5,000.00
NCHRP 24-25 Page 335 Phase II Appendices Scour Management Evaluation 5. FM 39 over Sanders Creek Bridge 091470064302038 in Limestone County, TX was constructed in 1977 and supports a rural major collector class road. This bridgeâs foundation is known with an NBI item 113 rating of â3â (scour critical and unstable). However, this bridge will be evaluated as if it had an unknown foundation to test the guidelines. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural major collector class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 7 Rural major collector classification NBI item 71 (bridge survey) 6 Waterway meets the minimum criteria â´Overtopping Frequency (guidelines) S Slight (once in 11-100 years) NBI item 60 (bridge survey) 7 Foundation is in good condition NBI item 61 (bridge survey) 7 Channel has only minor damage â´Scour Vulnerability (guidelines) 7 Countermeasures now make it stable â´Annual probability of failure (guidelines) 0.00025 A 1 in 4,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (47 years, according to the survey respondent) as follows:1-(1-0.00025)47, or about 0.012 (a 1 in 83 chance of failure in the next 47 years). This and other survey data are now used to calculate the risk of death as follows: 683,11$)2()/000,500($)012.0()0.1( 6 =â â â = â â â = peopleperson XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $20,000 and the risk of death is $11,683, automated scour monitoring is probably not warranted.
NCHRP 24-25 Page 336 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which the survey respondent estimated to be about $50,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $1,092,987. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 668,799,5$ )365()/700,2()11( 100 10/30.1$ 100 101/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 623,363,3$ /40 )365()/700,2()11( 100 10)/01.22($ 100 101)63.1()/96.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $11,256,277. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $131,504. Thus, scour countermeasures are probably warranted because the lifetime risk of failure is greater than the estimated cost of scour countermeasures. Is foundation reconnaissance and scour analysis warranted? We estimated the foundation reconnaissance and scour analysis costs to be about $10,000 and $5,000, respectively. Since this is only about 30% of the estimated cost of installing countermeasures, foundation reconnaissance and scour analysis are probably warranted before installing the countermeasures. Recommended management strategy This bridge has a known foundation, and requires action. If this bridge had an unknown foundation, the guidelines recommend the following steps to ensure the safety of the bridge: 1. Perform field reconnaissance to determine foundation type and depth. If the foundation is a spread footing, you could drill through the footing to determine elevation of the footing bottom. The parallel seismic test is generally the most effective NDT method. Assume that the foundation information from the field evaluation is accurate. If field reconnaissance is unsuccessful (no access for testing, poor signal from NDT, etc.), assume a foundation depth using local knowledge. This should be a conservative assumption. Spread footing depths are
NCHRP 24-25 Page 337 Phase II Appendices easily discovered and an assumption should not be necessary for this type of foundation. In other words, continue as if the foundation is known. 2. Evaluate scour using FHWA HEC-18 manual. 3. If scour analysis indicates that countermeasures are warranted, countermeasures should be designed using FHWA HEC-23 manual â or consider replacing or closing the bridge.
NCHRP 24-25 Page 338 Phase II Appendices Bridge #6 The Initial Survey Respondent Information Name Alan Kowalik E-mail Address akowali@dot.state.tx.us Job Title Bridge Inspection Supervisor Phone 512-416-2208 Job Description (In what way does your job involve bridge maintenance?) Supervise the bridge inspection program and the NBI Database Mailing Address 125 East 11th Street Austin, TX 78701 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. Big Elm Creek Road (#516) over Big Elm Creek â 1 span steel superstructured on concrete piling. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 486 5 Inventory Route 1-21-1-0000-0 8 Structure Number 090140AA0268002 19 Bypass, Detour Length (e.g. in miles) 6 26 Functional Classification of Inventory Route 06 27 Year Built 1986 29 Average Daily Traffic 32 49 Structure Length (e.g. in feet) 54 52 Deck Width, Out-to-Out (e.g. in feet) 20 60 Substructure 6 61 Channel and Channel Protection 6 71 Waterway Adequacy 5 109 Average Daily Truck Traffic Unknown 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 339 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 30 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 1080 ft2; Cost per unit area: 60 $/ft2; Cost Multiplier: 1 $64,800 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠1095 Value of time per adult * Use Table 3 ($/hr)  6.96 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠0 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $ Unknown Estimated cost of installing scour countermeasures $ No information Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $ N/A Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $3,000.00
NCHRP 24-25 Page 340 Phase II Appendices Scour Management Evaluation 6. Big Elm Creek Road over Big Elm Creek Bridge 12SR2250005 in Bell County, TX was constructed in 1986, and supports a rural minor arterial class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor arterial class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 6 Rural minor arterial classification NBI item 71 (bridge survey) 3 Waterway is a high priority for corrective action â´Overtopping Frequency (guidelines) O Occasional (once in 3-10 years) NBI item 60 (bridge survey) 6 Foundation is in satisfactory condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.0004 A 1 in 2,500 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (30 years, according to the survey respondent) as follows:1-(1-0.0004)30, or about 0.012 (a 1 in 83 chance of failure in the next 30 years). This and other survey data are now used to calculate the risk of death as follows: 0$)0()/000,500($)/012.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $20,000 and the risk of death is $0, automated scour monitoring may not be warranted.
NCHRP 24-25 Page 341 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which we estimated to be about $50,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $64,800. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 330,105$ )1095()/32()6( 100 6/30.1$ 100 61/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 992,62$ /40 )1095()/32()6( 100 6)/01.22($ 100 61)63.1()/96.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $233,122. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $2,781. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures. However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 342 Phase II Appendices Bridge #7 The Initial Survey Respondent Information Name Alan Kowalik E-mail Address akowali@dot.state.tx.us Job Title Bridge Inspection Supervisor Phone 512-416-2208 Job Description (In what way does your job involve bridge maintenance?) Supervise the bridge inspection program and the NBI Database Mailing Address 125 East 11th Street Austin, TX 78701 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. County Road 302 over Brazos River Slough â 2 simple span timber stringer on multiple timber piling. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 486 5 Inventory Route 1-21-1-0302-0 8 Structure Number 090740AA0128001 19 Bypass, Detour Length (e.g. in miles) 3 26 Functional Classification of Inventory Route 06 27 Year Built 1987 29 Average Daily Traffic 87 49 Structure Length (e.g. in feet) 52 52 Deck Width, Out-to-Out (e.g. in feet) 20.3 60 Substructure 7 61 Channel and Channel Protection 6 71 Waterway Adequacy 4 109 Average Daily Truck Traffic Unknown 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 343 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 31 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 713 ft2; Cost per unit area: 73 $/ft2; Cost Multiplier: 1 $52,049.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠1095 Value of time per adult * Use Table 3 ($/hr) ⧠6.96 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠0 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $ No information Estimated cost of installing scour countermeasures $ No information Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $ N/A Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $3,000.00
NCHRP 24-25 Page 344 Phase II Appendices Scour Management Evaluation 7. County Road 302 over Brazos River Slough Bridge 090740AA0128001 in Falls County, TX was constructed in 1987 and supports a rural minor arterial class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor arterial class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 6 Rural minor arterial classification NBI item 71 (bridge survey) 4 Waterway meets the minimum limits for no action â´Overtopping Frequency (guidelines) O Occasional (once in 3-10 years) NBI item 60 (bridge survey) 7 Foundation is in good condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.0004 A 1 in 2,500 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (31 years, according to the survey respondent) as follows:1-(1-0.0004)31, or about 0.012 (a 1 in 83 chance of failure in the next 31 years). This and other survey data are now used to calculate the risk of death as follows: 0$)0()/000,500($)/012.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $20,000 and the risk of death is $0, automated scour monitoring may not be warranted.
NCHRP 24-25 Page 345 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which we estimated to be about $50,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $64,800. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 183,143$ )1095()/87()3( 100 6/30.1$ 100 61/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 629,85$ /40 )1095()/87()3( 100 6)/01.22($ 100 61)63.1()/96.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $281,613. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $3,471. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures. However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 346 Phase II Appendices Bridge #8 The Initial Survey Respondent Information Name Alan Kowalik E-mail Address akowali@dot.state.tx.us Job Title Bridge Inspection Supervisor Phone 512-416-2208 Job Description (In what way does your job involve bridge maintenance?) Supervise the bridge inspection program and the NBI Database Mailing Address 125 East 11th Street Austin, TX 78701 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. County Road 2342 at BR Alligator Creek â 2 span continuous steel I-beam on steel piling. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 486 5 Inventory Route 1-21-1-0000-0 8 Structure Number 091100AA0878002 19 Bypass, Detour Length (e.g. in miles) 5 26 Functional Classification of Inventory Route 06 27 Year Built 1987 29 Average Daily Traffic 41 49 Structure Length (e.g. in feet) 44 52 Deck Width, Out-to-Out (e.g. in feet) 16.2 60 Substructure 6 61 Channel and Channel Protection 6 71 Waterway Adequacy 4 109 Average Daily Truck Traffic Unknown 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 347 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 31 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 713 ft2; Cost per unit area: 73 $/ft2; Cost Multiplier: 1 $52,049.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠1095 Value of time per adult * Use Table 3 ($/hr) ⧠6.96 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠0 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $ No information Estimated cost of installing scour countermeasures $ No information Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $ N/A Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $3,000.00
NCHRP 24-25 Page 348 Phase II Appendices Scour Management Evaluation 8. County Road 2342 over BR Alligator Creek Bridge 091100AA0878002 in Hill County, TX was constructed in 1987 and supports a rural minor arterial class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor arterial class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 6 Rural minor arterial classification NBI item 71 (bridge survey) 4 Waterway meets the minimum limits for no action â´Overtopping Frequency (guidelines) O Occasional (once in 3-10 years) NBI item 60 (bridge survey) 6 Foundation is in satisfactory condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 6 Not yet evaluated, but probably stable â´Annual probability of failure (guidelines) 0.0004 A 1 in 2,500 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (31 years, according to the survey respondent) as follows:1-(1-0.0004)31, or about 0.012 (a 1 in 83 chance of failure in the next 31 years). This and other survey data are now used to calculate the risk of death as follows: 0$)0()/000,500($)/012.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $20,000 and the risk of death is $0, automated scour monitoring may not be warranted.
NCHRP 24-25 Page 349 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which we estimated to be about $50,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $52,049. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 462,112$ )1095()/41()5( 100 6/30.1$ 100 61/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 257,67$ /40 )1095()/41()5( 100 6)/01.22($ 100 61)63.1()/96.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $231,768. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $2,857. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures. However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 350 Phase II Appendices Bridge #9 The Initial Survey Respondent Information Name Alan Kowalik E-mail Address akowali@dot.state.tx.us Job Title Bridge Inspection Supervisor Phone 512-416-2208 Job Description (In what way does your job involve bridge maintenance?) Supervise the bridge inspection program and the NBI Database Mailing Address 125 East 11th Street Austin, TX 78701 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. County Road 190 (Sandy Road) at Pin Oak Creek â 2 simple span steel I-beams on steel piles National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 486 5 Inventory Route 1-21-1-01901-0 8 Structure Number 091470AA0173001 19 Bypass, Detour Length (e.g. in miles) Dean end road 26 Functional Classification of Inventory Route 06 27 Year Built 1987 29 Average Daily Traffic 51 49 Structure Length (e.g. in feet) 31 52 Deck Width, Out-to-Out (e.g. in feet) 15.8 60 Substructure 5 61 Channel and Channel Protection 6 71 Waterway Adequacy 4 109 Average Daily Truck Traffic Unknown 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 351 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 31 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 490 ft2; Cost per unit area: 73 $/ft2; Cost Multiplier: 1 $35,770.00 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠1095 Value of time per adult * Use Table 3 ($/hr) ⧠6.96 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠0 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $ No information Estimated cost of installing scour countermeasures $ No information Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $ N/A Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $3,000.00
NCHRP 24-25 Page 352 Phase II Appendices Scour Management Evaluation 9. County Road 190 over Pin Oak Creek Bridge 091470AA0173001 in Limestone County, TX was constructed in 1987 and supports a rural minor arterial road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor arterial class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 6 Rural minor arterial classification NBI item 71 (bridge survey) 4 Waterway meets the minimum limits for no action â´Overtopping Frequency (guidelines) O Occasional (once in 3-10 years) NBI item 60 (bridge survey) 5 Foundation is in fair condition NBI item 61 (bridge survey) 6 Channel has widespread minor damage â´Scour Vulnerability (guidelines) 5 Analysis: stable; Survey: scour is within limits â´Annual probability of failure (guidelines) 0.00004 A 1 in 25,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (31 years, according to the survey respondent) as follows:1-(1-0.00004)31, or about 0.0012 (a 1 in 833 chance of failure in the next 31 years). This and other survey data are now used to calculate the risk of death as follows: 0$)0()/000,500($)/0012.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $20,000 and the risk of death is $0, automated scour monitoring may not be warranted.
NCHRP 24-25 Page 353 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which we estimated to be about $50,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $35,770. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 870,167$ )1095()/51()6( 100 6/30.1$ 100 61/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 393,100$ /40 )1095()/51()6( 100 6)/01.22($ 100 61)63.1()/96.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $304,033. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $377. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures. However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 354 Phase II Appendices Bridge #10 The Initial Survey Respondent Information Name Alan Kowalik E-mail Address akowali@dot.state.tx.us Job Title Bridge Inspection Supervisor Phone 512-416-2208 Job Description (In what way does your job involve bridge maintenance?) Supervise the bridge inspection program and the NBI Database Mailing Address 125 East 11th Street Austin, TX 78701 Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. County Road 421 at Pin Oak Creek â 2 span continuous steel I-beam on steel piles National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 486 5 Inventory Route 1-21-1-0421-0 8 Structure Number 091470AA0327001 19 Bypass, Detour Length (e.g. in miles) 1 26 Functional Classification of Inventory Route 06 27 Year Built 1987 29 Average Daily Traffic 51 49 Structure Length (e.g. in feet) 40 52 Deck Width, Out-to-Out (e.g. in feet) 16.1 60 Substructure 5 61 Channel and Channel Protection 5 71 Waterway Adequacy 3 109 Average Daily Truck Traffic Unknown 113 Scour Critical Bridges (2002 NBI Guidelines) U
NCHRP 24-25 Page 355 Phase II Appendices Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one) ⧠Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed 10 years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: 644 ft2; Cost per unit area: 73 $/ft2; Cost Multiplier: 1 $47,012 Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile ⧠Truck running cost $1.30 per mile ⧠Duration of detour * Use Table 2 (days) ⧠1095 Value of time per adult * Use Table 3 ($/hr) ⧠6.96 Average car occupancy rate 1.63 people ⧠Value of time for trucks $22.01 per hour ⧠Average detour speed 40 miles per hour ⧠Number of deaths from failure * Use Table 2 (Number of people) ⧠0 Cost for each life lost $500,000 ⧠* Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $ No information Estimated cost of installing scour countermeasures $ No information Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $ N/A Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $3,000.00
NCHRP 24-25 Page 356 Phase II Appendices Scour Management Evaluation 10. County Road 421 over Pin Oak Creek Bridge 091470AA0327001 in Limestone County, TX was constructed in 1987 and supports a rural minor arterial class road. This bridge has an unknown foundation depth, and it is further assumed that foundation records can not be found. Is it a high-priority bridge? This bridge supports a rural road, which is not a principal arterial, emergency route or provide direct access to other emergency services (e.g. hospital, fire stations, etc.). Thus, in this context this bridge is not considered a high priority bridge. Does the bridge meet the minimum performance level? The minimum performance level for a rural minor arterial class bridge, according to the guidelines, is 0.0005 â the threshold probability of failure that this bridge must outperform. To estimate this bridgeâs annual probability of failure, it is first necessary to estimate the overtopping frequency and scour vulnerability of this bridge, as in the table below. Data/Parameter (source) Value Interpretation NBI item 26 (bridge survey) 6 Rural minor arterial classification NBI item 71 (bridge survey) 3 Waterway is a high priority for corrective action â´Overtopping Frequency (guidelines) O Occasional (once in 3-10 years) NBI item 60 (bridge survey) 5 Foundation is in fair condition NBI item 61 (bridge survey) 5 Channel banks are eroding; major damage â´Scour Vulnerability (guidelines) 5 Analysis: stable; Survey: scour is within limits â´Annual probability of failure (guidelines) 0.00004 A 1 in 25,000 chance of failure in any given year This bridge meets the minimum performance level because the annual probability of failure is less than 0.0005. However, because the foundation is unknown, we need to determine the most cost effective way to manage this uncertainty. Is automated scour monitoring warranted? Automated scour monitoring is considered warranted if the lifetime risk of death is greater than the cost of automated scour monitoring. The lifetime probability of failure for this bridge can be computed from the annual probability of failure and its tentative remaining life (10 years, according to the survey respondent) as follows:1-(1-0.00004)10, or about 0.0004 (a 1 in 2,500 chance of failure in the next 10 years). This and other survey data are now used to calculate the risk of death as follows: 0$)0()/000,500($)/0004.0()0.1( 6 =â â â = â â â = peoplepersonyr XCPKR Ldeath Since the cost of automated scour monitoring was estimated to be $20,000 and the risk of death is $0, automated scour monitoring may not be warranted.
NCHRP 24-25 Page 357 Phase II Appendices Are scour countermeasures warranted? Scour countermeasures are considered warranted if the lifetime risk of failure is greater than the estimated cost of scour countermeasures, which we estimated to be about $50,000. The first step in estimating the risk of failure is to estimate the potential cost of failure, assuming that it would need to be replaced. The survey respondent estimated that a new bridge would cost about $47,012. The car and truck running cost associated with the detour for this bridge is computed from the survey data as follows: 978,27$ )1095()/51()1( 100 6/30.1$ 100 61/45.0$ 100100 1 32 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ = daysdaymimimi dADTCTCCrunning The cost of lost wages is computed from the survey data as follows: 732,16$ /40 )1095()/51()1( 100 6)/01.22($ 100 61)63.1()/96.6($ 100100 1 54 = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = â â â â¥â¦ â¤â¢â£ â¡ â +ââ âââ â ââ â = hrmi daysdaymitruckperper S dADTCTOCCwages When we include the cost of death, the total cost of bridge failure totals $91,723. Computing the risk of a scour-induced failure over the remaining life of the bridge is just the product of the lifetime probability of failure and the total cost of failure â about $37. Thus, scour countermeasures are probably not warranted because the lifetime risk of failure is less than the estimated cost of scour countermeasures. Recommended management strategy This bridge meets the performance standards for these guidelines and does not appear to warrant automated scour monitoring or countermeasures. However, because this bridge has an unknown foundation the guidelines strongly recommend that you follow the recommendations in the âBridge Closure Planâ section of this report. Furthermore, scour monitoring should be performed with every 2-yr routine bridge inspection for all bridges with unknown foundations. If the scour depth increases more than two feet from baseline conditions (as-built drawings or initial scour survey), action should be taken. The first action is to follow the âBridge Closure Planâ to take any necessary immediate action. Countermeasures should then be considered for this site; or close or replace the bridge. This two foot trigger can be adjusted based on local geotechnical and engineering considerations and should represent the depth of scour that the bridge engineer feels comfortable with for the individual bridge.
NCHRP 24-25 Page 358 Phase II Appendices Response to Evaluations Alan Kowalik, a bridge inspection branch manager, completed the bridge surveys for Keith Ramsey but forwarded the task of commenting on the evaluations to Mark McClellan, a bridge scour engineer. Mark McClellan commented via phone that the guidelines appear to be a good first step, but that they would benefit from better indicators of scour vulnerability. He also stated that he does not think that NBI substructure code (NBI item 60) is a reliable indicator of a foundationâs vulnerability.
NCHRP 24-25 Page 359 Phase II Appendices APPENDIX G. SCOUR EVALUATION FORMS AND TABLES This appendix collects into one place all of the basic forms and tables that a practitioner will need in order to implement the scour risk management guidelines. Thus, this appendix is intended to help the practitioner who has already read the main report implement the guidelines efficiently. Data Collection The following three-page bridge survey (see Appendix F) provides a useful checklist for the input data needed to implement the scour guidelines. It also reproduces useful information from Tables 3, 8, 9, 10, and 11 in the main report.
NCHRP 24-25 Page 360 Phase II Appendices Bridge #_____________ Page 1 Respondent Information Name E-mail Address Job Title Phone Job Description (In what way does your job involve bridge maintenance?) Mailing Address Bridge Description Please provide a general description of the bridge including its name, location, route, and water body. National Bridge Inventory (NBI) Data Please provide the following information for the bridge. This information should be available in the NBI database. Please provide the NBI Database Values consistent with those required in the 2002 NBI Coding Guide, and specify the units (where appropriate). NBI Item No. NBI Item Description NBI Database Value 1 State Code 5 Inventory Route 8 Structure Number 19 Bypass, Detour Length (e.g. in miles) 26 Functional Classification of Inventory Route 27 Year Built 29 Average Daily Traffic 49 Structure Length (e.g. in feet) 52 Deck Width, Out-to-Out (e.g. in feet) 60 Substructure 61 Channel and Channel Protection 71 Waterway Adequacy 109 Average Daily Truck Traffic 113 Scour Critical Bridges (2002 NBI Guidelines)
NCHRP 24-25 Page 361 Phase II Appendices Page 2 Undocumented Assumptions Please provide the following information for the bridge which in not documented in the NBI database. Description User Input Bridge Type (check only one)  Simple Span(s)  Continuous Span(s) over 100 ft. Remaining life of bridge in years. If this bridge has already failed, report the actual lifetime of the bridge before it failed years Total Bridge Rebuilding Cost, if known. If unknown, estimate the cost by multiplying the bridge area by the cost per unit area as shown in Table 1 and the ADT cost multiplier as shown in Table 2. If estimated, provide the assumptions used in the spaces below: Bridge Area: ________ft2; Cost per unit area: ________$/ft2; Cost Multiplier: ________ $ Economic Loss Data Please provide the following economic factors to be associated with the failure of this bridge. Either check the box confirming that the default factor is to be used or provide a different value. Description Default Value User-Provided Value Car running cost $0.45 per mile  Truck running cost $1.30 per mile  Duration of detour * Use Table 2 (days)  Value of time per adult * Use Table 3 ($/hr)  Average car occupancy rate 1.63 people  Value of time for trucks $22.01 per hour  Average detour speed 40 miles per hour  Number of deaths from failure * Use Table 2 (Number of people)  Cost for each life lost $500,000  * Please select an appropriate value from the reference table listed. Cost of Analysis or Corrective Actions Provide estimates for the following costs. Keep in mind that these costs may depend on a number of factors, e.g., the number of piers, abutments, etc. Also keep in mind that the guidelines include many significant broad assumptions, so significant effort is not warranted in estimating this data. Description User Input Estimated cost of installing automated scour monitoring $ Estimated cost of installing scour countermeasures $ Estimated cost of field reconnaissance to determine foundation type and depth (nondestructive testing, borings, etc.) $ Estimated cost to evaluate scour (survey, hydrology, and hydraulics analysis, if unavailable) $
NCHRP 24-25 Page 362 Phase II Appendices Table 1 Cost of Bridge Construction Page 3 Bridge Superstructure Type Total Cost ($/ft2) Reinforced concrete flat slab; simple span $50-65* Reinforced concrete flat slab; continuous span $60-80* Steel deck/girder; simple span $62-75* Steel deck/girder; continuous span $70-90* Pre-stressed concrete deck/girder; simple span $50-70* Pre-stressed concrete deck/girder; continuous span $65-110* Post-tensioned, cast-in-place, concrete box girder cast on scaffolding; span length <=240 ft $75-110 Steel Box Deck/Girder: Span range from 150 ft to 280 ft $76-120 For curvature add a 15 percent premium segmental concrete box girders; span range from 150 ft to 280 ft $80-110 Movable bridges; bascule spans & piers $900-1500 Demolition of existing bridges: Typical $9-15 Bascule spans & piers $63 * Increase the cost by twenty percent for phased construction. Source: http://www.dot.state.fl.us/structures/Manuals/LRFDSDG2002AugChap11.pdf visited on January 12, 2005. Table 2 Bridge Failure Statistics versus Average Daily Traffic Average Daily Traffic (ADT) Cost Multiplier for Early Replacement Detour Duration (days) Number of Lives Lost ADT < 100 1.0 1,095 0 100 < ADT < 500 1.1 730 1 500 < ADT < 1000 1.25 548 2 1000 < ADT < 5000 1.5 365 2 ADT > 5000 2.0 183 5* â 10â * Not an interstate or arterial. â Interstate or arterial. Table 3 Values of Time by State State Value of time ($/hour) State Value of time ($/hour) Alabama $6.29 Montana $5.89 Alaska $8.31 Nebraska $6.51 Arizona $6.88 Nevada $6.76 Arkansas $5.83 New Hampshire $7.38 California $8.27 New Jersey $8.48 Colorado $7.85 New Mexico $6.51 Connecticut $8.75 New York $8.59 Delaware $7.70 North Carolina $6.72 District of Columbia $11.43 North Dakota $6.04 Florida $6.65 Ohio $7.08 Georgia $7.06 Oklahoma $6.14 Guam $5.41 Oregon $7.29 Hawaii $7.24 Pennsylvania $7.09 Idaho $6.46 Puerto Rico $4.35 Illinois $7.61 Rhode Island $7.54 Indiana $6.67 South Carolina $6.29 Iowa $6.31 South Dakota $5.73 Kansas $6.66 Tennessee $6.45 Kentucky $6.34 Texas $6.96 Louisiana $6.16 Utah $6.72 Maine $6.60 Vermont $6.83 Maryland $8.15 Virgin Islands $5.58 Massachusetts $8.93 Virginia $7.71 Michigan $7.80 Washington $8.06 Minnesota $7.85 West Virginia $6.01 Mississippi $5.65 Wisconsin $6.95 Missouri $6.79 Wyoming $6.41 State wage data is from http://www.bls.gov/oes/current/oessrcst.htm, visited on January 12, 2006. This table assumes that the value of time is equal to 41% of the mean hourly wage, as proposed by José A. Gómez-Ibáñez, William B. Tye, Clifford Winston, âEssays in Transportation Economics and Policy: A Handbook in Honor of John R. Meyerâ, 1999.
NCHRP 24-25 Page 363 Phase II Appendices Scour Risk Probability Tables Tables 12 â 14 from the main report are reproduced here to help the practitioner estimate the probability of scour failure. Table 18 Overtopping Frequency Waterway Adequacy (NBI Item 71 Code) Functional Class: (NBI Item 26 Code) (0) (1) (2) (3) (4) (5) (6) (7) (8) (9) (N) Principal Arterials, Interstates (01, 11) O O O O S S S R N Freeways, Expressways (12) Other Principal Arterials (02, 14) Minor Arterials (06, 16) Major Collectors (07, 17) F O O O S S S R N Minor Collectors (08) Locals (09, 19) B rid ge C lo se d U nu se d F F O O O S S R N Key: N = Never; R = Remote (T > 100 yr); S = Slight (T = 11â100 yr); O = Occasional (T = 3â10 yr); F = Frequent (T < 3 yr) Table 19 Scour Vulnerability Substructure Condition (NBI Item 60 Code) Channel Protection (NBI Item 61 Code) (0 ) F ai le d (1 ) I m m in en t F ai lu re (2 ) C ri tic al C on di tio n (3 ) S er io us C on di tio n (4 ) P oo r C on di tio n (5 ) F ai r C on di tio n (6 ) S at is fa ct or y co nd iti on (7 ) G oo d C on di tio n (8 ) V er y G oo d C on di tio n (9 ) E xc el le nt C on di tio n (N ) N ot A pp lic ab le (0) Failure 0 0 0 0 0 0 0 0 0 0 0 (1) Failure 0 1 1 1 1 1 1 1 1 1 N (2) Near Collapse 0 1 2 2 2 2 2 2 2 2 N (3) Channel Migration 0 1 2 2 3 4 4 4 4 4 N (4) Undermined Bank 0 1 2 3 4 4 5 5 6 6 N (5) Eroded Bank 0 1 2 3 4 5 5 6 7 7 N (6) Bed Movement 0 1 2 3 4 5 6 6 7 7 N (7) Minor Drift 0 1 2 3 4 6 6 7 7 8 N (8) Stable Condition 0 1 2 3 4 6 7 7 8 8 N (9) No Deficiencies 0 1 2 3 4 7 7 8 8 9 N (N) Not Over Water 0 1 N N N N N N N N N
NCHRP 24-25 Page 364 Phase II Appendices Table 20 Annual Probability of Scour Failure Overtopping Frequency (from Table 18) Scour Vulnerability (from Table 19) Remote (R) Slight (S) Occasional (O) Frequent (F) (0) Failed 1 1 1 1 (1) Imminent failure 0.01 0.01 0.01 0.01 (2) Critical scour 0.005 0.006 0.008 0.009 (3) Serious scour 0.0011 0.0013 0.0016 0.002 (4) Advanced scour 0.0004 0.0005 0.0006 0.0007 (5) Minor scour 0.000007 0.000008 0.00004 0.00007 (6) Minor deterioration 0.00018 0.00025 0.0004 0.0005 (7) Good condition 0.00018 0.00025 0.0004 0.0005 (8) Very good condition 0.000004 0.000005 0.00002 0.00004 (9) Excellent condition 0.0000025 0.000003 0.000004 0.000007 Minimum Performance Levels Table 27 from the main report is reproduced here to help the practitioner assess the maximum annual probability of scour failure that is acceptable for different bridge classes. Table 21 Minimum Performance Levels NBI Code Description Minimum Performance Level (Threshold Probability of Failure) Rural 01, 02 Principal Arterial â All 0.0001 06, 07 Minor Arterial or Major Collector 0.0005 08 Minor Collector 0.001 09 Local 0.002 Urban 11, 12, 14 Principal Arterial â All 0.0001 16 Minor Arterial 0.0002 17 Collector 0.0005 19 Local 0.002
