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Proposed Guideline for Reliability-Based Bridge Inspection Practices P a r t I
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3 This guideline describes a methodology for developing Risk-Based Inspection (RBI) practices for highway bridges.
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4Definitions Attributes: Characteristics that affect the reliability of a bridge or bridge element. Condition Attributes: Characteristics that relate to the current condition of a bridge or bridge element.
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Definitions 5 Risk: Combination of the probability of an event and its consequence. Risk Analysis: Systematic use of information to estimate the risk.
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6Introduction This guideline describes a methodology for developing Risk-Based Inspection (RBI) practices for highway bridges.
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Introduction 7 prestressed superstructure elements constructed in the past 5 years, a multi-girder steel bridge constructed more than 50 years ago, and a multi-girder reinforced concrete bridge constructed in 1963. 1.1 Process The process involves an owner (e.g., state)
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8 Proposed Guideline for Reliability-Based Bridge Inspection Practices 1.1.2 Purpose The purpose of this document is to provide guidance for bridge owners for conducting reliability-based assessments for determining the frequency and scope of inspections for typical highway bridges. This document is intended to be used by bridge owners for assessing their bridge inventories in order to prioritize inspection needs based on an engineering analysis that considers the bridge type, age, loading, condition, and other characteristics of a bridge.
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Introduction 9 improve both bridge and inspection reliability. Other industries are increasingly recognizing the limitations of prescribed inspection frequencies and are developing methodologies for efficiently assessing inspection needs, ensuring the safety and reliability of systems, and focusing inspection resources most effectively (1, 4–6)
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10 Proposed Guideline for Reliability-Based Bridge Inspection Practices failure and the associated consequences. The setting of inspection frequencies or intervals is not a rigid process, such as is the case for uniform or calendar-based inspection frequencies.
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Introduction 11 is required to estimate the reliability of bridge elements based on past experience, engineering knowledge, and a rational process to systematically assess bridges of common design and construction characteristics. The process involves engineers with experience and expertise in the performance of bridges within a particular operational environment using engineering judgment to assess the probability (likelihood)
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12 This section describes the methodology for reliability assessment of the bridge elements. Section 2.1 describes and defines failure as applied to typical bridge elements for the reliability assessment.
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Reliability Assessment of Bridge Elements 13 This condition description is widely understood and there is significant past experience in the conditions warranting a rating of 3 throughout the bridge inventory. This condition description is not absolute, but provides a frame of reference for the analyst considering the likelihood of damage occurring to a serious extent.
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14 Proposed Guideline for Reliability-Based Bridge Inspection Practices unlikely that severe damage (i.e., failure) would occur in the next 72 months.
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Reliability Assessment of Bridge Elements 15 In assessing the consequences of a given damage mode for a given element, the RAP must establish which outcome characterized by the CFs in Table 2 is the most likely. In other words, which scenario does it have the most confidence will result if the damage were to occur.
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16 Proposed Guideline for Reliability-Based Bridge Inspection Practices notes and sketches included in the file, and have an understanding of the scope and the methods of the inspections used for the bridges under consideration.
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17 This section describes the process of determining the inspection interval and scope based on the assessment completed as described in Chapter 2. This process leads to a prioritization of inspection needs, highlights critical damage modes for bridges, and results in an RBI practice.
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18 Proposed Guideline for Reliability-Based Bridge Inspection Practices This is a relatively easy task for elements where the OF is high and the CF is severe, and hence an interval of 12 months or less is needed. However, if the OF is remote and the CF is low, then it would also seem reasonable and justifiable that the inspection interval should be greater than the longest interval assumed in the OF assessment (72 months)
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Determination of Inspection Interval and Scope 19 3.1.2 Sampling When using the RBI approach, it may be appropriate to inspect a representative sample of a bridge element, using the inspection method identified. This can be used to reduce or limit inspection activities that provide little or no measure of increased benefit or that introduce risks that are unjustified.
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20 Proposed Guideline for Reliability-Based Bridge Inspection Practices 3.1.6 Quality Control/Quality Assurance Quality control (QC) and quality assurance (QA)
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21 4.1 Overview of Process The overall process for implementing an RBI is shown schematically in Figure 3. The process begins with the selection of a bridge or family of similar bridges to be analyzed.
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22 Proposed Guideline for Reliability-Based Bridge Inspection Practices current condition. For those bridges where past experience is greatest, uncertainty regarding both the development of the damage and the associated consequences is reduced.
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Establishing an RBI Program 23 simple design and there is significant experience and confidence in their performance. For example, bridge owners conduct a simple analysis of their inventory to determine bridges that are multi-girder, short span, and in generally good condition for assessment first.
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24 Proposed Guideline for Reliability-Based Bridge Inspection Practices 4.4 Software Development and Integration The processes for assessing the OFs, such as identifying and scoring key attributes of bridge elements, can be repetitive once established, and therefore lends itself to software implementations. Many of the attributes identified by the RAP may already be stored in existing databases and bridge management systems.
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25 1. American Petroleum Institute (API)
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26 27 A 1 Introduction 28 A 2 Damage Modes 28 A 2.1 Expert Elicitation for Credible Damage Modes 29 A 2.2 Example of Soliciting Expert Judgment for Damage Modes 30 A 3 Element Attributes 31 A 3.1 Screening Attributes 32 A 3.1.1 Qualitative Assessment of Elements and Details 32 A 3.2 Identifying Key Attributes 33 A 3.3 Ranking Attributes 34 A 4 Occurrence Factor Assessment 34 A 4.1 Estimating the Occurrence Factor 34 A 4.2 Calibration of Scoring Regime 35 A 4.3 Occurrence Factor Scale Numerical Estimates 36 A 4.4 Use of Deterioration Rate Data 37 A 4.5 Use of Surrogate Data 38 A 4.6 Rationale and Criteria Based on RAP Assessments A P P E N D I X A Guideline for Evaluating the Occurrence Factor
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Guideline for Evaluating the Occurrence Factor 27 A 1 Introduction The Occurrence Factor (OF) is used within an RBI to estimate the likelihood of serious damage (i.e., failure)
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28 Proposed Guideline for Reliability-Based Bridge Inspection Practices The following sections describe how a Reliability Assessment Panel (RAP) identifies the damage modes to be assessed, determines important attributes for each damage mode, and ranks and scores those attributes to support assessment of an individual bridge or families of bridges of nearly identical attributes, damage modes, and design.
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Guideline for Evaluating the Occurrence Factor 29 2. Identify damage modes: The facilitator poses a question to the RAP such as: "The inspection report indicates that the element is rated in serious condition.
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30 Proposed Guideline for Reliability-Based Bridge Inspection Practices The elicitation process is repeated for each key element of the bridge to develop a listing of damage modes to be considered in the analysis. For example, considering a typical steel girder bridge with a bare concrete deck and concrete piers and abutments, damage modes for each element of the bridge that might be identified by a RAP are shown in Table A4.
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Guideline for Evaluating the Occurrence Factor 31 that contribute to the durability of the bridge element may be a design attribute, such as the use of penetrating sealers as a preservation strategy. Loading attributes are characteristics that describe the loads applied to the bridge element that affect its reliability.
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32 Proposed Guideline for Reliability-Based Bridge Inspection Practices brittle fracture. For fracture-critical bridges in particular, inspection will provide no protection as the CIF occurs without any warning and before any detectable cracks are observed.
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Guideline for Evaluating the Occurrence Factor 33 given damage mode can be identified through expert elicitation of the RAP. For example, the facilitator could ask the following question pertaining to a particular damage mode, X: • Consider damage mode X for the subject bridge element.
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34 Proposed Guideline for Reliability-Based Bridge Inspection Practices supports the RAP assessment of the OF. For attributes that are ranked with high importance, a scale of 20 points can be assigned, 15 points for an attribute that has a moderate importance, and 10 points for an attribute that plays a minor role, but is still an important indicator.
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Guideline for Evaluating the Occurrence Factor 35 or decreased to provide suitable results. Since operational environments and design and construction practices vary, rankings for attributes and associated values may need to be adjusted.
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36 Proposed Guideline for Reliability-Based Bridge Inspection Practices category, where the likelihood in less than 1/100 but greater than 1/1,000. Estimates from deterioration rate information or from statistical modeling can also be used to support the categorization of the OF.
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Guideline for Evaluating the Occurrence Factor 37 Deterioration rate data typically describe the mean or average behavior of the bridge element based on the observed behavior of a population of similar elements. Statistical descriptors of the dispersion of the data, such as the standard deviation, may be provided and then used as indicators of the variability of the data.
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38 Proposed Guideline for Reliability-Based Bridge Inspection Practices inspection result is from an RBI procedure, i.e., the inspection was capable of identifying the necessary condition attributes. This allows all bridges that are of this same rating (and similar design, loading, and condition attributes)
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39 40 B 1 Introduction 41 B 1.1 Definitions 41 B 2 General Descriptions of Consequence Scenarios 42 B 2.1 Low Consequence Event 42 General Description 43 Requirements for Selection 43 B 2.2 Moderate Consequence Event 43 General Description 43 Requirements for Selection 46 B 2.3 High Consequence Event 46 General Description 46 Requirements for Selection 48 B 2.4 Severe Consequence Event 48 General Description 48 Requirements for Selection 50 B 3 Use of Expert Elicitation for Determining the Consequence Scenario 50 B 4 References A P P E N D I X B Guideline for Evaluating the Consequence Factor
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40 Proposed Guideline for Reliability-Based Bridge Inspection Practices B 1 Introduction Within an RBI, the Consequence Factor (CF) is used to categorize the outcome or the result of the failure of a bridge element due to a given damage mode.
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Guideline for Evaluating the Consequence Factor 41 In these cases, it is important that the rationale used to support the determination is recorded. There are many situations in which analysis and/or experience can be used to justify selecting one scenario over another.
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42 Proposed Guideline for Reliability-Based Bridge Inspection Practices failure scenario are described. This section is intended as guidance for evaluation.
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Guideline for Evaluating the Consequence Factor 43 Requirements for Selection In order to select the lowest consequence category, the user must be able to clearly demonstrate that the consequence of the damage will be benign. Generally speaking, this decision will most often be based on engineering judgment and experience.
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44 Proposed Guideline for Reliability-Based Bridge Inspection Practices poses no serious threat to the structural integrity of the bridge or to the safety of the public. Generally, damage that will require repairs that can be addressed in a programmed fashion (i.e., non-emergency)
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Guideline for Evaluating the Consequence Factor 45 the examples above. However, other types of fatigue cracks may be more serious.
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46 Proposed Guideline for Reliability-Based Bridge Inspection Practices be able demonstrate that a lower CF is justifiable. Very high load ratings (e.g., 150% of the minimum required)
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Guideline for Evaluating the Consequence Factor 47 Examples of high consequence events would include scenarios that require short-term closures for repairs, lane restrictions that have a major impact on traffic, load postings, or other actions that majorly affect the public. Situations where the selection of this CF may be appropriate are as follows: • Failure of a main member in a multi-girder bridge with sufficient load path redundancy.
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48 Proposed Guideline for Reliability-Based Bridge Inspection Practices quantifiably showed that the bridge had sufficient reserve capacity in the faulted condition, i.e., with one girder fractured, it might be reasonable to identify the event as having a moderate consequence. Guidance on such analysis exists in the literature and it can be performed for common bridges and common bridge types.
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Guideline for Evaluating the Consequence Factor 49 that shows that the failure scenario being considered is likely to be consistent with a severe consequence event. Examples of severe consequence events would include failure of the pin or hanger in a bridge with a suspended truss span or a two-girder system, or strand fractures in a pre- or posttensioned element that results in a non-composite member falling into a roadway below, such as what was observed in Washington Township, PA (2)
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50 Proposed Guideline for Reliability-Based Bridge Inspection Practices B 3 Use of Expert Elicitation for Determining the Consequence Scenario An expert elicitation of the RAP can be a useful tool for evaluating the appropriate CF for situations that are not well matched to the examples given above, or to establish basic ground rules for the assessment of common situations. The expert elicitation process can be used to establish or to build consensus among the RAP and to assist in identifying the most likely outcomes of damage modes assessed during the reliability analysis.
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51 A P P E N D I X C 52 C 1 Inspection Intervals 52 C 1.1 Important or Essential Bridges Guideline for Determining the Inspection Interval
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52 Proposed Guideline for Reliability-Based Bridge Inspection Practices C 1 Inspection Intervals Inspection intervals are determined based on the reliability analysis using a simple four by four matrix as shown in Figure C1, which illustrates a risk matrix for a typical highway bridge. Engineering judgment is required for establishing the specific divisions applied to the risk matrix; the divisions are generally applied to ensure that the likelihood of damage remains low during the interval between inspections, such that there are multiple inspections conducted before there is a high likelihood of failure occurring.
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Guideline for Determining the Inspection Interval 53 and toward the lower left corner of the matrix. For example, Figure C2 illustrates a risk matrix an owner could apply to bridges for which an additional measure of reliability is desired.
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54 A P P E N D I X D 55 D 1 Introduction 55 D 1.1 NDE Method Technical Readiness Levels and Costs 56 D 2 Inspection Methods and Technologies Inspection Technologies
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Inspection Technologies 55 D 1 Introduction This appendix provides general guidance for the inspection methods to be utilized in a risk-based inspection (RBI) practice.
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56 Proposed Guideline for Reliability-Based Bridge Inspection Practices D 2 Inspection Methods and Technologies The tables included in this section (Tables D4 through D9) qualitatively describe the reliability and effectiveness of NDE technologies and inspection methods including routine inspection and hands-on inspections.
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Inspection Technologies 57 Table D4. Symbolic guide to inspection method reliability and effectiveness.
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58 Proposed Guideline for Reliability-Based Bridge Inspection Practices Damage Mode or Mechanism Routine Visual Hands-On Visual Sounding IR GPR Impact Echo Chain Drag SAW Delamination/ debonding Overlay cracking Spalling/patches Table D7. Concrete deck overlays.
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59 61 Introduction 61 Scoring Scheme 62 Screening Attributes 62 S.1 Current Condition Rating 62 S.2 Fire Damage 63 S.3 Susceptible to Collision 63 S.4 Flexural Cracking 64 S.5 Shear Cracking 65 S.6 Longitudinal Cracking in Prestressed Elements 65 S.7 Active Fatigue Cracks Due to Primary Stress Ranges 65 S.8 Details Susceptible to Constraint-Induced Fracture (CIF) 66 S.9 Significant Level of Active Corrosion or Section Loss 66 S.10 Design Features 67 Design Attributes 67 D.1 Joint Type 67 D.2 Load Posting 67 D.3 Minimum Vertical Clearance 69 D.4 Poor Deck Drainage and Ponding 69 D.5 Use of Open Decking 69 D.6 Year of Construction 71 D.7 Application of Protective Systems 72 D.8 Concrete Mix Design 73 D.9 Deck Form Type 73 D.10 Deck Overlays 73 D.11 Minimum Concrete Cover 75 D.12 Reinforcement Type 76 D.13 Built-Up Member 76 D.14 Constructed of High Performance Steel 76 D.15 Constructed of Weathering Steel 77 D.16 Element Connection Type 78 D.17 Worst Fatigue Detail Category 78 D.18 Skew 78 D.19 Presence of Cold Joints 79 D.20 Construction Techniques and Specifications 79 D.21 Footing Type 79 D.22 Subsurface Soil Condition A P P E N D I X E Attribute Index and Commentary
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60 Proposed Guideline for Reliability-Based Bridge Inspection Practices 80 Loading Attributes 80 L.1 ADTT 81 L.2 Dynamic Loading from Riding Surface 81 L.3 Exposure Environment 82 L.4 Likelihood of Overload 82 L.5 Rate of De-icing Chemical Application 83 L.6 Subjected to Overspray 83 L.7 Remaining Fatigue Life 84 L.8 Overtopping/High Water 84 Condition Attributes 84 C.1 Current Condition Rating 85 C.2 Current Element Condition State 86 C.3 Evidence of Rotation or Settlement 86 C.4 Joint Condition 86 C.5 Maintenance Cycle 87 C.6 Previously Impacted 87 C.7 Quality of Deck Drainage System 88 C.8 Corrosion-Induced Cracking 88 C.9 General Cracking 89 C.10 Delaminations 89 C.11 Presence of Repaired Areas 90 C.12 Presence of Spalling 90 C.13 Efflorescence/Staining 91 C.14 Flexural Cracking 92 C.15 Shear Cracking 92 C.16 Longitudinal Cracking in Prestressed Elements 93 C.17 Coating Condition 93 C.18 Condition of Fatigue Cracks 94 C.19 Presence of Fatigue Cracks due to Secondary or Out of Plane Stress 94 C.20 Non-Fatigue-Related Cracks or Defects 94 C.21 Presence of Active Corrosion 95 C.22 Presence of Debris 95 References
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Attribute Index and Commentary 61 Introduction This section includes suggested attributes for the reliability assessment of bridges. Users can select attributes from this listing.
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62 Proposed Guideline for Reliability-Based Bridge Inspection Practices environment. The scoring scheme should effectively develop sound engineering rationale to support risk-based inspection practices.
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Attribute Index and Commentary 63 fire. Based on this observation, bridges that have experienced a fire may be screened from the reliability assessment until an inspection, which has been conducted approximately 12 months or more after the fire, confirms that the fire has not affected the typical durability characteristics of the bridge components.
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64 Proposed Guideline for Reliability-Based Bridge Inspection Practices The effects on the strength and the durability of a prestressed element due to flexural cracking are generally more significant than for a reinforced concrete element. Assessment Procedure.
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Attribute Index and Commentary 65 S.6 Longitudinal Cracking in Prestressed Elements Reason(s) for Attribute.
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66 Proposed Guideline for Reliability-Based Bridge Inspection Practices S.9 Significant Level of Active Corrosion or Section Loss Reason(s) for Attribute.
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Attribute Index and Commentary 67 Design Attributes D.1 Joint Type Reason(s) for Attribute.
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68 Proposed Guideline for Reliability-Based Bridge Inspection Practices depend on the traffic composition of the roadway below, such as the average daily truck traffic (ADTT)
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Attribute Index and Commentary 69 D.4 Poor Deck Drainage and Ponding Reason(s) for Attribute.
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70 Proposed Guideline for Reliability-Based Bridge Inspection Practices is presently modeled as a diffusion process, using Fick's Law, which depends on time, temperature, the permeability of the concrete, and the concentration of chlorides at the component's surface. Additionally, if the concrete has suffered damage, such as cracking or spalling, chlorides can more easily concentrate at the reinforcement, effectively expediting the corrosion process.
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Attribute Index and Commentary 71 2009 In 2008, language was introduced into the AASHTO LRFD Bridge Design Specifications which directly addressed the issue of CIF. The article provided prescriptive guidance to ensure that details susceptible to CIF are avoided.
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72 Proposed Guideline for Reliability-Based Bridge Inspection Practices An overlay is defined herein as an additional layer of protective material, which is applied on top of the concrete deck and that also serves as the riding surface. Overlays may consist of asphalt, latex-modified concrete, low-slump dense concrete, silica fume concrete, polymer concrete, or other materials.
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Attribute Index and Commentary 73 The permeability of a concrete mix depends on several factors including the water to cementitious ratio, the use of densifying additives, and the use of mix-improving additives. Supplementary cementitious materials such as fly ash, ground-granulated blast furnace slag, and silica fume have been shown to reduce permeability.
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74 Proposed Guideline for Reliability-Based Bridge Inspection Practices historically poor performance of bridge elements with inadequate cover. The depth of concrete cover characterizes how far corrosive agents need to travel in order to reach the embedded steel reinforcement.
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Attribute Index and Commentary 75 Assessment Procedure. This attribute is scored based on the actual, physical clear cover which with the specified bridge element operates.
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76 Proposed Guideline for Reliability-Based Bridge Inspection Practices can typically be identified from the structure's design plans. If suitable information is unavailable, engineering judgment should be used.
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Attribute Index and Commentary 77 Assessment Procedure. This attribute is scored based on whether or not the element is constructed using weathering steel and is detailed and located in a manner that minimizes the contact of the steel with de-icing chemicals and moisture.
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78 Proposed Guideline for Reliability-Based Bridge Inspection Practices Element connected with welds 15 points Element connected with rivets 7 points Element connected with HS bolts 0 points D.17 Worst Fatigue Detail Category Reason(s) for Attribute.
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Attribute Index and Commentary 79 superstructure. This may result in accelerated deterioration patterns including coating failure and section loss for steel members, corrosion damage in concrete members, and/or corrosion damage in the deck.
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80 Proposed Guideline for Reliability-Based Bridge Inspection Practices Assessment Procedure. Subsurface soil conditions susceptible to these effects are typically known to geotechnical engineers and/or maintenance personnel.
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Attribute Index and Commentary 81 For concrete bridges, high ADTT will likely have the most significant effect on the durability of the bridge deck. Superstructure components will be affected to a much lesser extent; if designed to modern standards, high ADTT may have little effect on the durability of superstructure components.
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82 Proposed Guideline for Reliability-Based Bridge Inspection Practices Assessment Procedure. The assessment procedure is similar to other environmental exposure classifications that are already in practice.
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Attribute Index and Commentary 83 critical roadways that may receive the focus of local maintenance crews for the application of deicing chemicals. Obviously, the more frequent the snowfall, the more often de-icing chemicals are likely to be applied.
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84 Proposed Guideline for Reliability-Based Bridge Inspection Practices that have longer remaining fatigue lives, there is a lower probability of failure due to fatigue cracking than for elements with shorter remaining fatigue lives. Assessment Procedure.
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Attribute Index and Commentary 85 an overall characterization of the general condition of the entire component. It is reasonable to assume that a given element that has already shown signs of damage is more likely to deteriorate to a serious condition than an element showing little or no signs of damage.
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86 Proposed Guideline for Reliability-Based Bridge Inspection Practices C.3 Evidence of Rotation or Settlement Reason(s) for Attribute.
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Attribute Index and Commentary 87 washing out joints, and periodic application of the sealers help preserve bridge elements and extend their service lives. Conversely, a bridge that does not receive periodic maintenance and preservation activities is likely to experience damage and deterioration much earlier in its service life, and deteriorate at a higher rate relative to a bridge receiving consistent, periodic maintenance.
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88 Proposed Guideline for Reliability-Based Bridge Inspection Practices consider when scoring this attribute include build-up at the deck inlet grates, clogged drains or pipes, section loss in pipes, etc. Deck drains directly onto superstructure or substructure components, or ponding on deck results from poor drainage 20 points Drainage issues resulting in drainage onto superstructure or substructure components, or moderate ponding on deck; effects may be localized 10 points Adequate quality 0 points C.8 Corrosion-Induced Cracking Reason(s)
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Attribute Index and Commentary 89 C.10 Delaminations Reason(s) for Attribute.
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90 Proposed Guideline for Reliability-Based Bridge Inspection Practices Significant amount of repaired areas 15 points Moderate amount of repaired areas 10 points Minor amount of repaired areas 5 points No repaired areas 0 points C.12 Presence of Spalling Reason(s) for Attribute.
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Attribute Index and Commentary 91 Assessment Procedure. This attribute is scored based on inspection results.
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92 Proposed Guideline for Reliability-Based Bridge Inspection Practices Crack widths equal to or less than 0.006 inches to 0.012 inches, depending on environment for reinforced concrete; crack widths equal to or less than 0.006 inches for prestressed concrete 10 points No flexural cracking 0 points C.15 Shear Cracking Reason(s) for Attribute.
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Attribute Index and Commentary 93 C.17 Coating Condition Reason(s) for Attribute.
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94 Proposed Guideline for Reliability-Based Bridge Inspection Practices C.19 Presence of Fatigue Cracks Due to Secondary or Out-of-Plane Stress Reason(s) for Attribute.
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Attribute Index and Commentary 95 or not the corrosion is active. This attribute may also be used as a screening tool in a reliability assessment.
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96 Proposed Guideline for Reliability-Based Bridge Inspection Practices 14.
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97 98 F 1 Introduction 98 F 2 Example 1: Prestressed Concrete Bridge 98 F 2.1 Bridge Profile 98 F 2.1.1 Overview 99 F 2.1.2 Concrete Bridge Deck 99 F 2.1.3 Prestressed Girders 99 F 2.1.4 Substructure 99 F 2.2 Assessment 100 F 2.2.1 Concrete Bridge Deck 102 F 2.2.2 Prestressed Girder 105 F 2.2.3 Substructure 106 F 2.3 Consequence Assessment 107 F 2.4 Scoring Summary 107 F 2.5 Criteria for a Family of Bridges 109 F 3 Example 2: Steel Girder Bridge 109 F 3.1 Bridge Profile 109 F 3.1.1 Overview 109 F 3.1.2 Concrete Bridge Deck 110 F 3.1.3 Steel Girders 110 F 3.1.4 Substructure 110 F 3.2 Assessment 110 F 3.2.1 Concrete Bridge Deck 112 F 3.2.2 Asphalt Overlay 112 F 3.2.3 Steel Girders 114 F 3.2.4 Substructure 115 F 3.3 Consequence Assessment 116 F 3.4 Scoring Summary 117 F 3.5 Inspection Data 117 F 4 Example 3: Reinforced Concrete Bridge 117 F 4.1 Bridge Profile 117 F 4.1.1 Overview 117 F 4.1.2 Concrete Bridge Deck 118 F 4.1.3 Reinforced Concrete Girders 118 F 4.1.4 Substructure 119 F 4.2 Assessment 119 F 4.2.1 Concrete Bridge Deck 121 F 4.2.2 Reinforced Concrete Girders 123 F 4.2.3 Substructure 124 F 4.3 Consequence 126 F 4.4 Scoring Summary 126 F 4.5 Inspection Data A P P E N D I X F Illustrative Examples
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98 Proposed Guideline for Reliability-Based Bridge Inspection Practices F 1 Introduction This section provides three illustrative examples of applying reliability-based analysis to establish an inspection interval and strategy. The first is an example of a bridge constructed with a superstructure composed of prestressed girders, the second example is a bridge with a multi-girder steel superstructure, and the third example is a multi-girder reinforced concrete superstructure.
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Illustrative Examples 99 F 2.1.2 Concrete Bridge Deck The deck for this structure was cast-in-place and constructed with normal concrete and epoxy-coated rebar. From the design plans, the concrete cover for the top of the deck is 1-½ inches.
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100 Proposed Guideline for Reliability-Based Bridge Inspection Practices consequence of damage was considered. The results are then summarized in a table that provides the maximum inspection interval based on the risk matrix and the IPN determined from the analysis.
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Illustrative Examples 101 Corrosion Profile, Concrete Bridge Deck Attribute Score D.4 Poor Deck Drainage and Ponding • The deck drainage system is of modern design and is effective 0 D.6 Year of Construction • Bridge constructed in 2006 0 D.7 Application of Protective Systems • Protective systems never applied to deck 10 D.8 Concrete Mix Design • Constructed of normal grade concrete, no admixtures 15 D.11 Minimum Concrete Cover • Design cover is 1.5 inches 10 D.12 Reinforcement Type • Epoxy-coated reinforcement used 0 L.3 Exposure Environment • Deck environment is moderate 10 L.5 Rate of De-icing Chemical Application • Rate of de-icing chemical application is moderate 15 C.5 Maintenance Cycle • Bridge receives regular, periodic maintenance 0 Corrosion Profile score 60 out of 140 Attributes were identified by the RAP that affected the reliability and durability of a bare concrete deck. These attributes include the corrosion profile score, plus attributes based on the loading and the condition of a particular deck.
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102 Proposed Guideline for Reliability-Based Bridge Inspection Practices Corrosion Damage, Concrete Bridge Deck Attribute Score C.9 General Cracking • No general cracking observed 0 C.10 Delaminations • No delaminations found 0 C.11 Presence of Repaired Areas • No repaired areas 0 C.12 Presence of Spalling • No spalling noted 0 C.13 Efflorescence/Staining • Minor efflorescence without rust observed 5 Corrosion Damage total 80 out of 290 Corrosion Damage ranking 1.1 Low This bridge deck is still relatively new, was built to modern standards for durability and corrosion resistance, and has very little damage accumulation. As a result, the deck received very low scores for the attributes identified.
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Illustrative Examples 103 Corrosion Profile, Prestressed Girder Attribute Score C.5 Maintenance Cycle • Bridge receives regular, periodic maintenance 0 Corrosion Profile point total 60 out of 140 The RAP then considered the identified damage modes for a prestressed girder element, identified and ranked attributes, and applied the scoring model for each damage mode as shown below. Bearing Area Damage, Prestressed Girder Attribute Score Corrosion Profile score 60 D.1 Joint Type • Bridge contains a closed joint system 0 C.4 Joint Condition • Joints are not leaking 5 C.8 Corrosion-Induced Cracking • No corrosion-induced cracking noted 0 C.9 General Cracking • No general cracking observed 0 C.11 Presence of Repaired Areas • No repaired areas 0 C.12 Presence of Spalling • No areas of spalling noted 0 Bearing Area Damage point total 65 out of 240 Bearing Area Damage ranking 1.08 Low Corrosion Between Beam Ends, Prestressed Girder Attribute Score Corrosion Profile score 60 C.8 Corrosion-Induced Cracking • No corrosion-induced cracking noted 0 C.10 Delaminations • No delaminations found 0 C.11 Presence of Repaired Areas • No repaired areas 0 C.12 Presence of Spalling • No spalling present 0 C.13 Efflorescence/Staining • No signs of efflorescence 0
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From page 103... ...
104 Proposed Guideline for Reliability-Based Bridge Inspection Practices Corrosion Between Beam Ends, Prestressed Girder Attribute Score Corrosion Between Beam Ends point total 60 out of 235 Corrosion Between Beam Ends ranking 1.02 Low Flexural/Shear Cracking, Prestressed Girder Attribute Score S.4 Flexural Cracking • No flexural cracking Pass S.5 Shear Cracking • No shear cracking Pass D.2 Load Posting • Bridge is not load posted 0 L.4 Likelihood of Overload • Likelihood of overload is low 0 C.14 Flexural Cracking • No flexural cracking 0 C.15 Shear Cracking • No shear cracking 0 Flexural/Shear Cracking point total 0 out of 55 Flexural/Shear Cracking ranking 0 Remote Strand Fracture, Prestressed Girder Attribute Score S.1 Current Condition Rating • Superstructure condition rating is greater than 4 Pass S.6 Longitudinal Cracking in Prestressed Elements • Significant cracking is not present Pass Corrosion Profile score 60 L.6 Subjected to Overspray • Bridge not over a roadway, not exposed to overspray 0 C.1 Current Condition Rating • Superstructure condition rating is 8 0 C.4 Joint Condition • Joints are present but not leaking 5 C.8 Corrosion-Induced Cracking • No corrosion-induced cracking noted 0 C.10 Delaminations • No delaminations found 0 C.11 Presence of Repaired Areas • No repaired areas 0 C.12 Presence of Spalling • No spalling present 0
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From page 104... ...
Illustrative Examples 105 Strand Fracture, Prestressed Girder Attribute Score C.16 Longitudinal Cracking in Prestressed Elements • No longitudinal cracking in the girders 0 Strand Fracture point total 65 out of 285 Strand Fracture ranking 0.91 Remote Based on the attributes identified by the RAP, the OF for the bearing area damage and corrosion between the beam ends was estimated to be Low (OF = 2)
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From page 105... ...
106 Proposed Guideline for Reliability-Based Bridge Inspection Practices Corrosion Damage -- Piers and Abutments, Substructure Attribute Score Corrosion Profile score 75 C.1 Current Condition Rating • Current substructure condition rating is 8 0 C.4 Joint Condition • Joints present but not leaking 5 C.8 Corrosion-Induced Cracking • No corrosion-induced cracking noted 0 C.9 General Cracking • No cracking observed 0 C.10 Delaminations • No delaminations found 0 C.11 Presence of Repaired Areas • No repaired areas present 0 C.12 Presence of Spalling • No spalling noted 0 C.13 Efflorescence/Staining • No signs of efflorescence 0 Corrosion Damage point total 80 out of 290 Corrosion Damage ranking 1.10 Low Based on the attribute scoring, the OF for the damage mode of "Corrosion Damage" was assessed to be Low (OF = 2)
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From page 106... ...
Illustrative Examples 107 for this bridge was reviewed and the bridge possessed a capacity far in excess of the required Inventory and Operating ratings. Hence, the RAP concluded that the loss of one girder would at most have a Moderate (CF = 2)
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From page 107... ...
108 Proposed Guideline for Reliability-Based Bridge Inspection Practices by the analysis, such as shear or flexural cracking, corrosion-induced cracking, spalling, or efflorescence, were either not present or minimal if the CS ratings for the element were CS 1 or CS 2. Therefore, for the prestressed girder element, elements that are rated as CS 1 and CS 2 would not have the damage characteristics the panel identified as key to the potential for serious damage to develop.
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From page 108... ...
Illustrative Examples 109 F 3 Example 2: Steel Girder Bridge F 3.1 Bridge Profile F 3.1.1 Overview This example bridge carries a state highway over a non-navigable river. The bridge was constructed in 1954 with a continuous steel girder superstructure, a non-composite reinforced concrete deck, and a reinforced concrete substructure (Figure F2)
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From page 109... ...
110 Proposed Guideline for Reliability-Based Bridge Inspection Practices The most recent inspection rated the deck condition as 6-Satisfactory. According to the inspection report, the underside of the deck has hairline transverse cracks, spaced 2 to 3 feet apart, with efflorescence stains.
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From page 110... ...
Illustrative Examples 111 Corrosion Profile, Concrete Bridge Deck Attribute Score D.4 Poor Deck Drainage and Ponding • No drainage problems noted 0 D.6 Year of Construction • Bridge constructed in 1954 6 D.7 Application of Protective Systems • Protective systems never applied to deck 10 D.8 Concrete Mix Design • Constructed of normal grade concrete, no admixtures 15 D.11 Minimum Concrete Cover • Design cover is between 1.5 inches and 2.5 inches 10 D.12 Reinforcement Type • Uncoated carbon steel reinforcement 15 L.3 Exposure Environment • Deck environment is moderate 10 L.5 Rate of De-icing Chemical Application • Rate of de-icing chemical application is high (100 times per year) 20 C.5 Maintenance Cycle • Maintenance cycle is at least limited 10 Corrosion Profile score 96 out of 140 Corrosion Damage, Concrete Bridge Deck Attribute Score S.1 Current Condition Rating • Current deck condition rating is greater than 4 Pass S.2 Fire Damage • No fire damage in the past 12 months Pass Corrosion Profile score 96 L.1 ADTT • ADTT is minor (130 vehicles)
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From page 111... ...
112 Proposed Guideline for Reliability-Based Bridge Inspection Practices Corrosion Damage, Concrete Bridge Deck Attribute Score C.13 Efflorescence/Staining • Moderate efflorescence without rust observed 10 Extent of Damage total 141 out of 290 Corrosion damage ranking 1.94 Low Based on the attributes identified by the RAP, the OF for corrosion damage was assessed to be Low (OF = 2)
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From page 112... ...
Illustrative Examples 113 Corrosion Damage, Steel Girder Attribute Score S.9 Significant Level of Active Corrosion or Section Loss • Active corrosion present is not alarming Pass D.5 Use of Open Decking • Bridge does not have an open deck 0 D.13 Built-Up Member • Element is built up 15 D.15 Constructed of Weathering Steel • Element not constructed with weathering steel 10 L.3 Exposure Environment • Exposure environment is moderate 10 L.5 Rate of De-icing Chemical Application • Rate of de-icing chemical application is high (100 times per year) 20 L.6 Subjected to Overspray • Superstructure is not subjected to overspray 0 C.4 Joint Condition • Joints are moderately leaking 15 C.7 Quality of Deck Drainage System • Drainage system is of adequate quality 0 C.17 Coating Condition • Element is painted, with steel exposed on bottom flanges 10 C.21 Presence of Active Corrosion • Significant active corrosion is present 20 C.22 Presence of Debris • Element has no debris 0 Corrosion Damage point total 100 out of 190 Corrosion Damage ranking 2.1 Moderate Fracture Damage, Steel Girder Attribute Score S.7 Active Fatigue Cracks due to Primary Stress Ranges • No active fatigue cracks due to primary stress Pass S.8 Details Susceptible to Constraint-Induced Fracture • No details susceptible to constraint induced fracture Pass D.3 Minimum Vertical Clearance • Bridge is not over a roadway, max vertical clearance 0 D.6 Year of Construction • Bridge constructed in 1954 20 D.14 Constructed of High Performance Steel • Element is not constructed of HPS/unknown 10 L.1 ADTT • ADTT is 130 vehicles 15
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From page 113... ...
114 Proposed Guideline for Reliability-Based Bridge Inspection Practices Fracture Damage, Steel Girder Attribute Score L.7 Remaining Fatigue Life • Remaining fatigue life is unknown 10 C.6 Previously Impacted • Bridge has not been impacted before 0 C.19 Presence of Fatigue Cracks due to Secondary or Out-of-Plane Stress • No fatigue cracks present 0 C.20 Non-Fatigue-Related Cracks or Defects • No fatigue cracks present 0 Fracture Damage point total 55 out of 125 Fracture Damage ranking 1.76 Low The RAP analysis of key attributes for the damage modes indicated that the steel superstructure has a moderate likelihood of fatigue damage (OF = 3) , a moderate likelihood of developing corrosion damage (OF = 3)
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From page 114... ...
Illustrative Examples 115 Corrosion Damage -- Piers and Abutments, Substructure Attribute Score Corrosion Profile score 86 C.1 Current Condition Rating • Current substructure condition rating is six 5 C.4 Joint Condition • Joints are significantly leaking onto substructure 20 C.8 Corrosion-Induced Cracking • Moderate corrosion-induced cracking noted 10 C.9 General Cracking • Presence of minor general cracking 5 C.10 Delaminations • Minor localized delaminations on footings 5 C.11 Presence of Repaired Areas • No repaired areas present 0 C.12 Presence of Spalling • Significant spalling with exposed reinforcement present on piers 20 C.13 Efflorescence/Staining • Moderate efflorescence without rust staining 10 Substructure Elements point total 161 out of 290 Substructure Elements ranking 2.22 Moderate Based on the attribute scoring, the RAP estimated the OF was Moderate (OF = 3) for corrosion damage for the piers and abutments.
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From page 115... ...
116 Proposed Guideline for Reliability-Based Bridge Inspection Practices than or equal to this bridge, had similar skew, had similar girder spacing, and had a non-composite deck. In all cases, none of the bridges collapsed, though some displayed minor sagging.
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From page 116... ...
Illustrative Examples 117 F 3.5 Inspection Data Table F4 summarizes the information from the RAP analysis to be included in the RBI procedure to be used for this bridge. The identified screening criteria for fatigue cracking due to primary stresses and significant section loss are included as special emphasis items.
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From page 117... ...
118 Proposed Guideline for Reliability-Based Bridge Inspection Practices From the design plans, the minimum cover was determined to be 1-13⁄16 inches. Based on the most recent inspection report, the deck is considered to be in CS 6-Satisfactory.
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From page 118... ...
Illustrative Examples 119 F 4.2 Assessment The primary elements of this bridge are a concrete bridge deck, reinforced concrete girders, and piers and abutments. For the concrete bridge deck element, the typical damage mode identified was corrosion damage (concrete cracking and spalling)
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From page 119... ...
120 Proposed Guideline for Reliability-Based Bridge Inspection Practices Corrosion Profile, Concrete Bridge Deck Attribute Score D.6 Year of Construction • Bridge constructed in 1963 6 D.7 Application of Protective Systems • Waterproof penetrating sealer applied, frequency unknown 5 D.8 Concrete Mix Design • Constructed of normal grade concrete, no admixtures 15 D.11 Minimum Concrete Cover • Design cover is between 1.5 inches and 2.5 inches 10 D.12 Reinforcement Type • Uncoated carbon steel reinforcement 15 L.3 Exposure Environment • Deck environment is moderate 10 L.5 Rate of De-icing Chemical Application • Rate of de-icing chemical application is moderate 15 C.5 Maintenance Cycle • Maintenance cycle is at least limited 10 Corrosion Profile score 86 out of 140 Corrosion Damage, Concrete Bridge Deck Attribute Score S.1 Current Condition Rating • Current deck condition rating is greater than four Pass S.2 Fire Damage • No fire damage in the past 12 months Pass Corrosion Profile score 86 L.1 ADTT • ADTT is high (5,500 vehicles) 20 C.1 Current Condition Rating • Current deck condition rating is 6 5 C.8 Corrosion-Induced Cracking • Moderate corrosion-induced cracking noted 10 C.9 General Cracking • Moderate general cracking observed 10 C.10 Delaminations • No delaminations noted 0 C.11 Presence of Repaired Areas • No repaired areas 0 C.12 Presence of Spalling • No spalling noted 0
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From page 120... ...
Illustrative Examples 121 Corrosion Damage, Concrete Bridge Deck Attribute Score C.13 Efflorescence/Staining • Minor efflorescence without rust observed 5 Corrosion Damage total 136 out of 290 Corrosion Damage ranking 1.88 Low Based on the attributes identified by the RAP, the OF for corrosion damage in the deck was estimated as Low (OF = 2)
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From page 121... ...
122 Proposed Guideline for Reliability-Based Bridge Inspection Practices Bearing Area Damage, Reinforced Concrete Girder Attribute Score C.4 Joint Condition • Joints are leaking but sealant is still in fair condition 15 C.8 Corrosion-Induced Cracking • No corrosion-induced cracking noted 0 C.9 General Cracking • No general cracking observed 0 C.11 Presence of Repaired Areas • No repaired areas 0 C.12 Presence of Spalling • Moderate spalling in several locations, no exposed reinforcement noted. 15 Bearing Area Damage point total 111 out of 240 Bearing Area Damage ranking 1.85 Low Corrosion Between Beam Ends, Reinforced Concrete Girder Attribute Score Corrosion Profile score 81 C.1 Current Condition Rating • Current condition rating is 5 20 C.6 Previously Impacted 20 C.8 Corrosion-Induced Cracking • No corrosion-induced cracking noted 0 C.9 General Cracking • No general cracking observed 0 C.10 Delaminations • Unknown 20 C.11 Presence of Repaired Areas • No repaired areas 0 C.12 Presence of Spalling • Moderate spalling in several locations (due to impact)
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From page 122... ...
Illustrative Examples 123 Flexural Cracking, Reinforced Concrete Girder Attribute Score D.2 Load Posting • Bridge is not load posted 0 L.4 Likelihood of Overload • Likelihood of overload is moderate 10 C.14 Flexural Cracking • Hairline flexural cracking noted 15 Flexural Cracking point total 25 out of 45 Flexural Cracking ranking 2.22 Moderate Shear Cracking, Reinforced Concrete Girder Attribute Score S.5 Shear Cracking • No shear cracking present Pass D.2 Load Posting • Bridge is not load posted 0 L.4 Likelihood of Overload • Likelihood of overload is moderate 10 C.15 Shear Cracking • No shear cracking 0 Shear Cracking point total 10 out of 45 Shear Cracking ranking 0.88 Remote The attribute scoring indicated an OF of Moderate (OF = 3) for corrosion between beam ends and flexural cracking, an OF of Low (OF = 2)
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From page 123... ...
124 Proposed Guideline for Reliability-Based Bridge Inspection Practices Corrosion Profile, Substructure Attribute Score D.11 Minimum Concrete Cover • Minimum design concrete cover is 2-½ inches 0 D.12 Reinforcement Type • Reinforcement is uncoated carbon steel 15 L.3 Exposure Environment • Exposure environment is moderate 10 L.5 Rate of De-icing Chemical Application • Rate of de-icing chemical application is moderate 15 C.5 Maintenance Cycle • Maintenance cycle is at least limited 10 Corrosion Profile point total 81 out of 140 Corrosion Damage -- Piers and Abutments, Substructure Attribute Score Corrosion Profile score 81 C.1 Current Condition Rating • Current substructure condition rating is five 20 C.4 Joint Condition • Joints are moderately leaking onto substructure 15 C.8 Corrosion-Induced Cracking • Localized cracking near delaminations noted 5 C.9 General Cracking • Presence of moderate general cracking 10 C.10 Delaminations • Unknown 20 C.11 Presence of Repaired Areas • No repaired areas present 0 C.12 Presence of Spalling • Moderate spalling with exposed reinforcement present 15 C.13 Efflorescence/Staining • No efflorescence noted 0 Concrete Elements point total 166 out of 290 Concrete Elements ranking 2.28 Moderate Based on their analysis, the RAP assessed that the likelihood of failure due to corrosion damage was moderate for the pier and abutments (OF = 3)
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From page 124... ...
Illustrative Examples 125 case, the bridge carries a high-volume highway over another, lower-volume roadway. The roadway on the bridge carries 22,000 vehicles a day, and the roadway below the bridge carries 60 vehicles a day.
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From page 125... ...
126 Proposed Guideline for Reliability-Based Bridge Inspection Practices For the reinforced concrete substructure, areas of delaminations are present in several locations and both abutments have areas of spalling with exposed reinforcement. Here, the most likely damage mode will result in spalling of the concrete.
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From page 126... ...
Illustrative Examples 127 each of which have the potential to result in debris falling into the roadway below the bridge. As a result, the RAP determined that enhanced inspection for corrosion damage was needed as part of the RBI procedure.
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Key Terms
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