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Inspection and Management of Bridges with Fracture-Critical Details (2005)

Chapter: Chapter Three - Results of Survey

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Suggested Citation:"Chapter Three - Results of Survey." National Academies of Sciences, Engineering, and Medicine. 2005. Inspection and Management of Bridges with Fracture-Critical Details. Washington, DC: The National Academies Press. doi: 10.17226/13887.
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Suggested Citation:"Chapter Three - Results of Survey." National Academies of Sciences, Engineering, and Medicine. 2005. Inspection and Management of Bridges with Fracture-Critical Details. Washington, DC: The National Academies Press. doi: 10.17226/13887.
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Suggested Citation:"Chapter Three - Results of Survey." National Academies of Sciences, Engineering, and Medicine. 2005. Inspection and Management of Bridges with Fracture-Critical Details. Washington, DC: The National Academies Press. doi: 10.17226/13887.
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Suggested Citation:"Chapter Three - Results of Survey." National Academies of Sciences, Engineering, and Medicine. 2005. Inspection and Management of Bridges with Fracture-Critical Details. Washington, DC: The National Academies Press. doi: 10.17226/13887.
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Suggested Citation:"Chapter Three - Results of Survey." National Academies of Sciences, Engineering, and Medicine. 2005. Inspection and Management of Bridges with Fracture-Critical Details. Washington, DC: The National Academies Press. doi: 10.17226/13887.
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Suggested Citation:"Chapter Three - Results of Survey." National Academies of Sciences, Engineering, and Medicine. 2005. Inspection and Management of Bridges with Fracture-Critical Details. Washington, DC: The National Academies Press. doi: 10.17226/13887.
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Suggested Citation:"Chapter Three - Results of Survey." National Academies of Sciences, Engineering, and Medicine. 2005. Inspection and Management of Bridges with Fracture-Critical Details. Washington, DC: The National Academies Press. doi: 10.17226/13887.
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This chapter summarizes the findings of the survey. One of the objectives of this survey was to gather information on fracture-critical structures and how bridge owners define, identify, inspect, and manage FCBs. Information related to structural failures and how owners have addressed or developed retrofit policies and strategies was also collected. In addition, what owners see as the most relevant research needs related to FCBs was solicited. Specifically, the survey was intended to collect data in varying levels related to the following: • How FCMs are presently defined, documented, and managed; • Inspection frequencies and procedures; • Methods for calculating remaining fatigue life; • Qualification and training of inspectors; • Available and needed training; • Locally owned bridges; • Experience with FCM fractures and problem details; • Examples of where an inspection program prevented failures; • Cost of inspection programs; • Retrofit techniques used; • NDE methods used; • As-built versus as-designed; • Fabrication methods and fabrication inspection; and • Impact of staff turnover. BACKGROUND A detailed questionnaire intended to identify and characterize specific issues related to FCBs was developed and distributed to all state and Canadian provincial DOTs and various other transportation authorities within the United States. The sur- vey was divided into four parts. Part I (General) collected general information related to FCBs and was the screening portion of the survey to determine whether participants should continue on to the other three sections. Part II (Inspection and Classification) was intended to identify the policies and approaches used to inspect FCBs. In addition, this section also requested specific data related to the classification and number of FCBs in an owner’s inventory. Part III (Failures) requested specific details about each owner’s experiences with respect to problems with both FCBs and non-FCBs. Owners were requested to provide information about all 24 types of failures, whether they were the result of fatigue and fracture or for other reasons (e.g., impact, overload, or corrosion). This section also differentiated between failures that occurred before and after the FCP was initiated (around 1975 for most agencies) and before and after the FCB inspec- tion program became regulation (around 1988 for most agen- cies). Part IV (Retrofit Procedures) contained a series of questions that sought to acquire information about how own- ers deal with failed bridges and/or subsequently develop pro- cedures to improve redundancy. This section also requested that individuals provide opinions on future research needs related to FCBs. Overall, the response to the survey was reasonably thor- ough. After it was sent out, several owners indicated that they did not have the ability to retrieve the data requested with respect to the breakdown of the structure types that were clas- sified as FCBs in their inventory. This was the result of limi- tations of the software that they used to manage their bridge databases. Most however were able to provide the detailed data, which are included in Appendix B. A list of survey respondents is included in Appendix C. Two states, Pennsylvania and Oklahoma, provided addi- tional documentation that described their general inspection procedures. [More information can be found on the website of each state (http://www.dot.state.pa.us/ and http://www. okladot.state.ok.us/).] According to the document provided, the procedures used by Oklahoma are based somewhat on those of the Pennsylvania DOT. That document provides guidance on how to prioritize FCBs for inspection criteria and intervals based on remaining fatigue life, fatigue detail, material properties, and so forth. In addition, issues related to FCBs were discussed with sev- eral colleagues, the project panel, AASHTO T-14 at the July 2003 meeting in Baltimore, and participants at the FHWA FCB workshop held in Orlando in November 2004. Many of the comments from these conversations are also reported here as anecdotes. SUMMARY OF RESPONSES TO PART I—GENERAL In this section, agencies were asked to provide their definition of an FCB. For the most part, the responses were consistent and nearly all agencies referred to or quoted the definition CHAPTER THREE RESULTS OF SURVEY

25 The greatest scatter in the responses appeared to be related to three-girder bridges and twin-steel “tub” girders. As indi- cated earlier, because respondents classified the bridge type based on their opinion owing to the lack of a formal policy by their agency, it is clear that different results would be obtained from different people. Interestingly, this implies that the same structural configuration may be classified as fracture-critical in one portion of a state and non-fracture-critical in another. As indicated in Table 2, agencies were also asked to iden- tify and classify other types of bridges as fracture or non- fracture-critical. The responses were limited to this question. However, approximately one-third of the agencies indicated that there are other bridge types they classify as fracture- critical. Some of these included timber bridges, post-tensioned concrete, and steel-tied arch bridges. Suspension bridges were also typically classified as fracture-critical owing to the main cables. SUMMARY OF RESPONSES TO PART II— INSPECTION AND CLASSIFICATION Part II of the survey provided considerable information as to the number of bridge types in the inventories of the respond- ing agencies. Specific structural configurations were identified by most agencies. Unfortunately, not all agencies provided data for this set of questions, because they were not able to extract the information from their databases. As can be seen, approximately 11% percent of the steel bridge inventory is classified as fracture-critical, based on the agencies that responded to this question. The percentage ranged from approximately 10% to up to 30%, depending on the agency. However, the majority of these bridges (about 75%) were built before 1975 (around the time the FCP was introduced by AASHTO). This is most likely for several reasons, including increases in quality control and the more stringent (and hence more costly) material and fabrication costs demanded by the FCP. In addition, the lack of apparent redundancy of FCBs was an obvious undesirable feature and led many agencies to move away from building such struc- tures. Because most of the FCBs in the U.S. inventory were designed before 1975, these bridges contain fatigue details known to be poor and those that are susceptible to out-of- plane distortion. It should also be noted that the “modern” fatigue design provisions were introduced into the specifi- cations beginning around 1973. Hence, most of the bridges built before 1975 were designed using the older, nonconser- vative fatigue design provisions. Fortunately, the loading used for fatigue design and the analytical models were, in most cases, quite conservative. FCBs designed beginning in the early 1980s were detailed to minimize out-of-plane distortion cracking and minimize the use of low-fatigue resistance details (D, E, and E′). In addi- tion, these bridges were built with material having improved fracture toughness requirements and shop inspection. provided by the AASHTO LRFD Bridge Design Specifica- tions. However, although the definition provided was consis- tent, how it is applied to various structure types was much more variable. A question was posed in tabular format asking the respondent to classify various types of bridges as fracture- critical or non-fracture-critical. The question and responses are summarized in Table 2. Most respondents indicated that their answers were based both on general policy where applicable and their own opinion. As is apparent from the summarized data, there is consid- erable inconsistency in how owners apply the definition of FCBs. The only structural configurations that all respondents classified the same were a two-girder system (fracture-critical) and multisteel tub girder bridges (non-fracture-critical). The respondents were generally more conservative in their application of the definition than the AASHTO Manual for Condition Evaluation and Load and Resistance Factor Rating (LRFR) of Highway Bridges (3) [identical in this respect to the predecessor Manual for Condition Evaluation of Bridges (54)] and the Bridge Inspector’s Reference Manual (29). Interestingly, truss bridges with two truss lines were clas- sified as non-fracture-critical by a few owners. In discussing this issue with one of the respondents, they indicated that they were primarily referring to riveted trusses because individual members were internally redundant and fracture of the entire tension chord was very unlikely. When asked if they would consider riveted two-girder bridges as non-fracture-critical if there were riveted cover plates, they indicated that they might if there was more than one cover plate, but that this would have to be considered on a case-by-case basis. Therefore, it appears that internal member redundancy is sometimes equated with load-path redundancy, or it at least lowers an owner’s concern regarding load-path redundancy. Description Two-girder bridges Three-girder bridges Three-girder bridges with girder spacing Multigirder bridges with girder spacing Truss bridges Two-girder bridges fabricated using HPS 70W Truss bridges fabricated using HPS 70W Single-steel ìt ub” girder bridges Twin-steel “tub” girder bridges Multisteel “tub” girder bridges Other (post-tensioned, timber, steel cross girders, etc.) Fracture-Critical Yes 38 9 10 3 34 31 28 32 22 0 13 No 0 21 32 28 3 1 2 5 12 34 3 TABLE 2 SURVEY RESPONSES TO QUESTION 3 (How would you categorize the following bridges?)

The two most common types of fracture-critical structural systems are not surprisingly two-girder bridges and trusses. The combination of these two structural systems comprises approximately 83% of all FCBs. About one-half of these struc- tures (41%) are riveted structures, the remaining being fully welded or welded and bolted. Inspection Issues Many agencies (60%) require that inspectors successfully complete the National Highway Institute fracture-critical train- ing course and indicated that experience with various NDT techniques is helpful. NDT (discussed in detail in Appendix A), such as magnetic-particle testing, dye-penetrant testing, or ultrasonic testing, was required when warranted. These techniques were also used depending on the bridge’s age, average daily truck traffic (ADTT), stress level, and condi- tion. No information on the use of special devices such as boroscopes for inspection of details that cannot be accessed was provided. Several states rotate field inspectors and shop inspectors and report that the cross transfer of knowledge is beneficial. Many respondents are concerned about shrinking budgets and staff, personnel turnover, and lost expertise. Many agen- cies are also concerned about contracting out inspections to consultants; however, no firm examples to warrant such con- cern were provided. These concerns are usually coupled with the perceived need for improved documentation. Concerns have been expressed about locally owned bridges and bridges less than 20 ft (6 m) in span not receiving any or enough atten- tion from skilled inspectors. Consultants are often hired to do this work and results are often reported to be inadequate. A local municipality was contacted as well as two local con- sultants and there does not appear to be a unified approach to the inspection of local bridges. Some, depending on size, location, and use, are inspected more rigorously than others. Some states may override the decisions of the local govern- ments. Some state agencies have expressed the desire to be able to review the quality of local inspectors to ensure that they are adequately trained and performing inspections con- sistent with required standards. Although the inspectors’ training is considered to be ade- quate, many engineers have noted how the training in fatigue and fracture is not adequate. Engineers are reportedly not learning lessons from fatigue and fracture incidents because of a lack of understanding. There is concern that they are not able to predict future problem details. Better education in this area in engineering programs as well as short courses for practicing engineers could lead not only to better new bridge designs but also to more qualified and knowledgeable engi- neers to participate in maintenance and inspections. In addition, approximately 65% of respondents indicated that special procedures were followed when inspecting FCBs. No details were provided as to what these special procedures 26 included, however, it can be assumed that they involve a more thorough inspection requiring a greater level of effort. Some of the following cost data were briefly discussed in chapter two. Costs associated with bridge inspection take up a considerable portion of each agency’s budget. It is believed by many owners that inspection costs associated with FCBs con- sume a large portion of the budget dedicated to inspection. Questions were asked to determine if this belief is consistent with actual practice. There was considerable variation in the data obtained. This is partly because the survey did not clearly indicate to respondents what cost comparisons should be included. However, for a given agency, it is reasonable to assume that the person completing the survey compared the same items for each type of inspection. Therefore, although the response from different agencies cannot be compared, relative increases indicated from an individual survey are comparable. Owners were asked to estimate what, if any, additional costs are incurred when inspecting an FCB. Surprisingly, the answers ranged from 0% to 6,000%, with most agencies indi- cating increases of from 200% to 500%. It should be noted that only two owners mentioned that there was none or neg- ligible increases in costs associated with inspecting FCBs. (Some agencies did not reply to these questions.) The indi- viduals who indicated that there were significant additional costs provided solid reasons for these increases, the most common of which were as follows: • Additional costs associated with the use of special- ized access equipment such as a snooper, manlift, or rigging. In many cases, non-FCBs can be inspected from the ground with binoculars. FCBs require “arm- length” access. • Additional costs associated with traffic control to close lanes to permit the access equipment to be placed on or below the bridge. Indirect costs associated with lane closures were estimated by one agency to be $11,000 per lane per hour of closure. Thus, if inspection required two lanes to be closed for 3 h, there would be a cost of $66,000 to the motoring public. • Increased costs associated with additional employee- hours required to conduct a detailed hands-on inspection. • Additional costs associated with needs to more frequently perform NDT. • Many states inspect FCBs at greater frequency than non- FCBs. This in itself may raise costs assuming that there are no other increases. As stated, some agencies inspect FCBs more frequently than non-FCBs. As part of the survey, owners were asked to provide the intervals at which inspections are conducted. There was moderate variation in the responses, with intervals ranging from 2 to 5 years. Certainly, the condition of a given structure has a significant influence on the interval between inspections. Based on discussions with some owners, inter- vals of 6 months or even less are sometimes used in unusual

27 cases where warranted. However, some agencies did not dis- tinguish between the FCB and non-FCB bridges when deter- mining the interval between inspections. The survey revealed that there are differences in how owners inspect FCBs. When asked if the entire bridge is inspected or just the FCMs in detail, there appeared to be no clear consensus. Apparently, in the training course, Michael Baker, Jr., has indicated that if there are FCMs the entire bridge should be subjected to hands-on inspection. Some owners see no increase in costs by inspecting the entire bridge in greater detail, whereas others indicated that only the FCMs are included to reduce costs. Some owners noted that hands-on inspection is encountering significant prob- lems in non-FCBs as well. Inspectors reported that variance of as-built conditions when compared with what is shown on the plans is a prob- lem. Documentation of the as-built details could be very use- ful. Examples include SR-422 in Pennsylvania (37), the Hoan Bridge (38), and other bridges with shelf–plate details for lateral bracing that were not built as shown in the plans and were not the same quality welding as expected. This and other problem details are discussed further in Appendix A. In conversations with owners and bridge engineers it is often expressed that inspection intervals and the level of scrutiny should be flexible; being determined by the states and different for different bridge situations. Many individu- als have expressed a desire to see such levels based on risk, which might include ADTT and the type of fatigue details. On the other hand, public and private inspectors want a cook- book procedure, owing to inadequate knowledge, not getting paid to make judgments, and concerns about liability if they do make judgments. A proper balance must be found between these two needs and the safety of the bridge. For example, John W. Fisher, Professor Emeritus of Lehigh University, expressed similar views during a personal interview con- ducted in June 2004. Dr. Fisher also stated that efforts related to inspection of a given bridge should be a function of the material used in the fabrication of the bridge. For example, a bridge constructed of HPS 70W material will not need to be inspected as often as bridges made from other steel, at least with respect to issues of fatigue and fracture. He suggests the following inspection scenario for new bridges. After con- struction, a bridge should be inspected every 2 years for the first 4 years to identify any critical issues, which are usually manifest early in the life of a bridge. If the condition of the bridge is acceptable after 4 years, then the inspection inter- val could be increased to 5 years for the next 10 to 15 years. The inspection frequency should be reconsidered and the inspection interval decreased, if needed, every 15 years. Follow-up questions were asked of some agencies to deter- mine how many states have centralized teams, including engi- neers and NDE technicians, that perform all the FCB inspec- tions in the state. This is common in low population states such as Wyoming, because there are a limited number of per- sonnel anyway. However, many of the larger states, such as Texas and Minnesota, also have centralized statewide teams. They noted the advantages of working with a snooper and continuity in having the same team do the inspections repeat- edly. Other larger states assign inspections to regional divi- sions that do the non-FCB inspections as well—or there is a mix of some inspections of major or troublesome FCBs done by centralized teams, whereas inspections of smaller, benign FCBs are done by regions. Approximately 20% of responding agencies have done more rigorous analysis to determine which members or por- tions of members are actually in tension and hence consid- ered fracture-critical. The objective of this question was to ascertain if owners actually analyze a structure to determine which members, if they were to fail, would lead to the col- lapse of the bridge. For example, there may be many tension members in a large truss that are subject to tensile dead and live load stresses. However, through more advanced analy- sis, it can usually be shown that there may only be a few of these critical members that if lost as a result of fracture would lead to collapse. One example is Texas, which has its cen- tralized team do this type of analysis in advance of inspect- ing all of their FCBs. Unfortunately, this question does not seem to have been worded clearly enough to ensure that this is the level of analy- sis being referred to. Thus, it seems that some agencies indi- cating “analysis” is performed were not referring to the advanced analysis described previously. Nevertheless, it appears that a very small percentage of owners would perform this level of analysis and only in large critical structures. In addition to the cost, inspectors and owners see many advantages to the hands-on fracture-critical inspections. They reported finding numerous problems with fatigue and corro- sion that might not otherwise have been discovered. There are also reports of finding these problems in non-FCMs; therefore, hands-on inspection is good for all members of all bridges. These hands-on inspections are also reported to be useful for the purpose of bridge management; that is, for pri- oritizing bridges as part of an overall bridge replacement and rehabilitation program. Inspection and Failures The following question (no. 13) was asked related to inspec- tion of FCBs and whether or not it has prevented any failures: Has the inspection of a fracture-critical bridge(s) ever iden- tified a condition that has clearly prevented a fracture and the subsequent collapse of the structure? Respondents were informed that the objective of this ques- tion was to identify specific cases or examples whereby the additional inspection efforts dedicated to FCBs prevented a failure that would have occurred had the inspection not been

carried out. However, case examples that would not warrant a “yes” were provided. For example, the discovery of typical out-of-plane distortion cracks, which usually take years to become critical, would not warrant a response of “yes.” Fur- thermore, inspections that found fractured members would also not warrant a response of “yes” because the inspection did not prevent the fracture and the bridge did not fail. Interestingly, approximately 30% of the agencies that replied to this question answered “yes.” However, in describ- ing the specific case where this had occurred, the fracture of the member had already taken place. Thus, the respondent should have answered “no.” Note that these responses also indicate cases where FCMs had fractured, and bridges did not collapse, and therefore would add to the few cases described in chapter two (see Figures 16 and 17). When one of the owners who completed the survey was asked why they answered “yes” to the question, they indi- cated that although the fracture had occurred, the bridge did not collapse. In addition, there was no indication of any sag- ging of the structure. Hence, because the inspection found the fracture before any loss of structural integrity, the structure could be repaired before there was any more significant dam- age. (It should be noted that the fracture in question occurred in May 2003 under moderate temperatures. Had the frac- ture occurred in the winter during a cold period, it could have been much worse and significant damage introduced. Furthermore, the forensic investigation revealed that the frac- ture had occurred less than a few days to a maximum of one week before being discovered. Therefore, it is almost purely coincidental that the fracture was found before any additional damage occurred. Ironically, the owner had developed retro- fit drawings and was about to let the construction contract to retrofit the bridge to prevent this type of problem at the time the failure occurred.) Nevertheless, when the responses were closely reviewed and adjusted to properly answer the question, the percentage of “yes” respondents drops to 23%, which is still significant because failures were prevented. Journal articles have reported on instances of fractures that were found during inspections; for example, the Edgewood Road Bridge in Cedar Rapids, Iowa (31). This bridge was being inspected by a private firm and a large fracture in the top flange of the twin-box structure was discovered at several loca- tions. Although contracting inspections out worries many bridge owners, this firm was apparently doing a good job. Frac- tures in the Paseo Bridge on I-35 in Kansas City, Missouri, were noticed only when an 8 in. (200 mm) gap opened at the expansion joint (39). Only 5% of those responding indicated that the use of HPS would influence how they view FCBs. Most believed that if a member fails, it does not matter what type of steel was used and that owing to the lack of redundancy inherent 28 in the bridge, there was no advantage. There appeared to be little recognition of the significantly superior toughness of HPS in decreasing the potential for fracture of a given member. In addition, most agencies (79%) did not feel that eliminating poor fatigue details, say less than a Category C fatigue detail, would influence their decisions with respect to inspection frequency or the level of detail in new bridges. Some states base their inspection frequency on the types of fatigue details that are on the bridge and use this (and other data) to determine how often the bridge should be inspected and with what level of detail. With respect to fatigue, it is commonly observed that by using simplified structural analysis methods the calculations for many bridges indicated no remaining fatigue life or even “negative” fatigue life. These calculations imply that fatigue cracking should be observed presently or in the near future on these bridges. However, such bridges typically show no signs of fatigue-related problems. (This does not include cracking from secondary stresses, such as web-gap cracking, because this type of cracking is not explicitly considered in fatigue rating calculations.) When asked about their agency’s policy regarding cases when this inconsistency occurs, results were that one of the owners responding had a formal policy regarding this common problem. Most indicated that they do a more rigorous analysis or field instrumentation on a case- by-case basis. Even then, these efforts are mostly limited to use on larger or critical bridges. However, other factors, such as route, ADTT, existing condition, type of steel, and age also influence the decision to use the more advanced meth- ods. Weigh-in-motion or advanced three-dimensional analy- ses are used by approximately 10% and 32% of the agencies, respectively, as needed. Interestingly, field instrumentation and load testing was used by approximately 45% of the agen- cies at one time or another. However, this is somewhat mis- leading, because an agency may have only used field instru- mentation once in 10 years. Thus, although nearly half of those responding have indicated they have used field instru- mentation to improve fatigue life predictions at one time, it is not used very often. SUMMARY OF RESPONSES TO PART III—FAILURES This section collects information relating only to bridge fail- ures. Cracking associated with fatigue that did not result in fracture was not included as a failure. For example, out-of- plane distortion cracks were not to be counted as failures. However, fractures that resulted from a fatigue crack were to be included. Respondents were asked to distinguish between failures that occurred before and those that occurred after the implementation of the FCB inspection program. Failures in FCBs and non-FCBs were to be identified separately. Fur- thermore, owners were asked to distinguish between failures that were the result of impact, scour, and so forth, and those caused by fatigue or fracture. Unfortunately, the data col- lected related to these questions were not as complete as was desired and were very difficult to quantify.

29 The results of this section revealed that there have been very few failures of FCBs that were the result of fatigue or fracture. As discussed chapter two, with the exception of the Silver Bridge (1967) (Figure 1) and the Mianus River Bridge (1983) (Figure 4), no bridges have completely collapsed as a result of brittle fracture caused by fatigue or a flaw in the past 45 years. As discussed in chapter two, the failure of the Silver Bridge led to the development and implementation of the national bridge inspection program in the United States. Interestingly, the fail- ure of the Mianus River Bridge in 1983 occurred after the implementation of that program. As discussed in chapter two, however, the failure of the Mianus River Bridge did lead to the development and implementation of the FCB inspection pro- gram, which was put into practice in 1988. As mentioned earlier, respondents were asked to distin- guish between all failures (fracture-critical and non-fracture- critical) that occurred before and after the implementation of the FCB inspection program. Unfortunately, many agen- cies did not indicate when the failure occurred. Based on the limited responses, it appears that most were not because the bridge was fracture-critical and could not have been prevented through inspection. Note that this is not to say that FCBs have not failed catastrophically for reasons such as overloads, scour, or impact. (A bridge posted for 3 tons that has collapsed because a 30-ton truck attempted to cross it did not fail sim- ply because it was fracture-critical.) Rather, the data suggest that there are very few failures that have been caused by fatigue or brittle fracture in the absence of overloads, impact, scour, or corrosion. Owners were asked if any special or formal investigative procedures were implemented when a failure had occurred to identify the cause of the fracture. Few of the agencies indi- cated that any formal procedures exist, although limited inves- tigations were conducted on most failures. In other cases, the girder was repaired and no formal investigation was conducted. Therefore, failure investigations appear to be conducted at various levels on a case-by-case basis. Another interesting observation from the survey data is related to the lack of owners documenting and archiving reports or data related to failures. Although many failures throughout the United States over the past 30 years are gener- ally known, interestingly many states did not include these failures when replying to this section of the survey. It is assumed that the individual who responded had no personal knowledge of the failure or that the individuals who did either did not get the survey, left the organization, or simply forgot. This also implies that not all owners keep a centralized data- base of failures within their jurisdiction that can be easily accessed. Thus, new employees may not be adequately informed of previous problems on a given structure or when a problem previously studied arises. The issue of individuals retiring or leaving state DOTs was reviewed in NCHRP Synthesis of Highway Practice 313: State DOT Outsourcing and Private-Sector Utilization (55). A primary objective of that report was to provide guidance on the outsourcing of major program responsibility of state trans- portation agencies. The outsourcing of the decision-making process and issues associated with procuring and adminis- tering outsourced activities are also discussed. SUMMARY OF RESPONSES TO PART IV— RETROFIT PROCEDURES This section was intended to identify any standard practices that have been developed to improve the redundancy of FCBs. Approximately 92% of the agencies responding to this ques- tion have not developed such policies. In addition, agencies were asked to identify any research needs related to FCBs. A summary of the “yes” votes for each of the suggested potential research topics is summarized here. The top three are highlighted in bold. • Develop guidelines related to advanced structural analy- sis procedures to better predict service load behavior in FCBs (8). • Develop advanced fatigue-life calculation proce- dures taking into account the lack of visible cracks for FCBs (9). • Field monitoring for FCBs (10). • Crack arrest capabilities of bridge steel (3). • Establish evaluation procedures for advanced large deformation and member loss (7). • Develop advanced analyses techniques and proce- dures to investigate alternate load paths, redundancy, and bridge collapse (10). • Develop retrofit procedures to add redundancy (1). Although some examples were provided, owners were also asked to suggest other potential research topics. Only a few agencies suggested additional research topics. Three owners indicated that inspection frequency and extent for fracture- critical (and all) bridges should be risk-based and related to ADTT and fatigue details. FCBs on very low ADTT roads should not need the same frequency of inspection as those on busy Interstates. Two states indicated that they already con- duct inspections as a function of ADTT. For these states, if the ADTT is less than 1,000 (150 for the other state), they are not required to perform the detailed inspections associated with FCBs. Another potential topic mentioned was that the loading of the structure should be checked when investigating the potential for collapse. NCHRP Report 406 (34), discussed in chapter two, provides a procedure that has been used suc- cessfully in practice. One respondent suggested that some guidance as to the extent of damage, analysis methods, mag- nitude of live load, impact, and so forth, be specified so that a designer can determine if there is the potential for collapse. It should be noted that the 2005 AASHTO LRFD is to have

substantial additional commentary on how to analyze and address the loading and analysis issues for FCBs. The results of the survey also suggest that the applica- tion of the AASHTO definition of FCMs and FCBs needs clarification, because there is considerable variability in the classification of structures. One owner suggested that research be conducted to eval- uate and identify issues related to overhead sign bridges and high-mast lighting towers because these are often fracture- critical structures. They further indicated that these structures actually give them more problems than bridges; however, there are no standardized inspection and fabrication specifi- cations for these structures. SUMMARY OF SURVEY RESULTS The results of the survey can be summarized as follows: • Owners use a consistent definition for FCBs that is in agreement with that provided by AASHTO. However, how they establish which bridges are fracture-critical is much more variable. A bridge that is determined to be fracture-critical in one state may not be identified as such in another state. Often, the decision is based on engineering judgment. • Additional costs associated with the inspection of FCBs can be considerable, both in terms of direct dollar costs and the additional indirect costs to the public as a result of lane closures and traffic delays. Most agencies reported inspection costs that were 2 to 5 times greater for FCBs than for non-FCBs. Increases in inspection costs of 10 to 50 times have been reported for some structures. 30 • There are two documented collapses of FCBs where the structure catastrophically failed. One is the Point Pleas- ant Bridge that failed before any initiatives related to the FCP and NBIS. The second is the Mianus River Bridge, which failed before the implementation of the FCB inspection program. Other failures that were the result of unreasonable overloads should not be directly attributed to the circumstance of the bridge being frac- ture-critical. Other failures have occurred as a result of scour or impact; but again, these failures are indepen- dent of bridge type. • There have been several fractures of bridges identified as FCBs over the last 30 years that have occurred with- out collapse or resulting in fatality. The apparent ade- quacy of alternate load paths within all of these structures has provided substantial redundancy, although they were not designed as such. • Owners identified the following as the most important areas for future research related to FCBs: – Develop load models, criteria for extent of damage, and guidelines related to advanced structural analy- sis procedures to better predict service load behavior in FCBs and the behavior after fracture of an FCM, including dynamic effects from the shock of the frac- ture and, if necessary, large deformations. – Develop advanced fatigue-life calculation procedures taking into account a lack of visible cracks for FCBs. – Provide field monitoring for FCBs. – Develop rational risk-based criteria for inspection frequency criteria and level of detail based on ADTT, date of design, and fatigue detail categories present. – Evaluate fracture-critical issues related to sign, signal, and light supports. (Respondents indicated that these structures give them more problems than bridges).

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TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 354: Inspection and Management of Bridges with Fracture-Critical Details explores the inspection and maintenance of bridges with fracture-critical members (FCMs), as defined in the American Association of State Highway and Transportation Officials’ Load and Resistance Factor Design (LRFD) Bridge Design Specifications. The report identifies gaps in literature related to the subject; determines practices and problems with how bridge owners define, identify, document, inspect, and manage bridges with fracture-critical details; and identifies specific research needs. Among the areas examined in the report are inspection frequencies and procedures; methods for calculating remaining fatigue life; qualification, availability, and training of inspectors; cost of inspection programs; instances where inspection programs prevented failures; retrofit techniques; fabrication methods and inspections; and experience with fracture-critical members fractures and problems details.

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