Status of NCHRP 12-82 (1)

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Status of NCHRP 12-82 (1)Developing Reliability-Based

Bridge Inspection Practices: Case Studies of the Methodology

Glenn A. Washer, PIRobert Connor, Co-PI

This investigation was sponsored by TRB under the NCHRPProgram. Data reported are work in progress. The contents ofthis presentation has not been reviewed by the project panel orNCHRP, nor do they constitute a standard, specification, orregulation.

AASHTO – SCOBS , T-18 June 2013

NCHRP 12-82 Goals• Goal: Improve the safety and reliability of

bridges – focusing inspection efforts where most needed

• Optimize the use of resources– Better match inspection requirements to

inspection needs – Develop a rational process for assessing

inspection needs using reliability theories

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Component Lifetime Characteristics

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Time to corrosion initiation for RCTypical lifetime performance


Reliability-Based Inspection (RBI)

• What can go wrong?– Identify damage modes for elements– Deterioration mechanisms

• How likely is it? • Categorization based on reliability characteristics of a

bridge elements• Based on expert judgment and expert elicitations

• Past experience• Analysis of existing or potential damage modes• Deterioration data if available (and relevant)

• What are the consequences?– How important is it?

• Semi-quantitative methodology

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Reliability/Risk Matrix• Set inspection interval

based on this assessment • Selected to ensure low

likelihood of severe damage between inspections

• 12-96 months• Maintenance

inspections

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Potential Benefits of RBI• Better, more effective and purposeful

inspections– Inspection plan (scope and interval) supported by

engineering assessment by RAP• Vs. Calendar-based inspection strategy

– Rational inspection strategies• Flexible intervals based on need and engineering

analysis• Allocate resources more effectively

– Focus inspections resources where most needed• Improved bridge reliability and safety

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Guidelines and Report from Phase I

• Available by request from NCHRP– Draft guidelines and draft final report

• Overview of the method• Background on reliability concepts• Assessment processes

• Occurrence (likelihood) and consequence factors• Identifying and assessing attributes • Consequence assessment• Inspection intervals

• Maintenance, initial, start-up and inspections• Criteria for reassessment

• Inspection scope• Starting an RBI program

• Scope of analysis, training, integration

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Phase II: Case Study Work Plan

• Conduct analysis in 2 States– Steel / PS – Oregon and Texas

• Assemble and train panel, conduct analysis, identify criteria for setting inspection practice (schedule and scope)

• Perform back-casting on sample of bridges to analyze effectiveness of methodology– Validate the approach– Quantitative data on effectiveness and accuracy of the

approach– Foundation for implementation

• Modify/improve guidelines, complete final report with verification data

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RBI Process

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Progress on Phase II Case Studies

• 2 families of bridges– Oregon

• Prestressed concrete– Texas

• Steel superstructures• Reliability Assessment Panels (RAP)

– Inspection, management, materials, structures and maintenance

– Academia– Industry

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RAP Meetings• Oregon April, 2013• Texas May 2013• Training in the RBI process

– Pre-meeting webinar– 5 slide modules

• Analysis of family of bridges– Deck, superstructure and substructure analysis– Consequences of identified damage modes

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Damage Modes and Attributes• RAP identifies most likely damage modes• Attributes contributing to that damage

mode– Deterioration mechanisms– Ex. Corrosion, fatigue

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Consequences

• Scenarios considered by RAP according to category descriptions from guidelines

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Highlights• Uncommon damage modes • Element-level data • Expert elicitation process

– Exercises – Consensus building

• Common attributes• Consequence analysis

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Other ongoing work …….

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98765432

600

500

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300

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100

0

Data

Freq

uenc

y

17.37 7.925 68414.19 7.627 50812.98 7.454 69512.03 7.233 85812.18 7.223 7699.724 6.945 70

Shape Scale N

0-1011-2021-3031-4041-5051 and more

Variable

Histogram of 0-10, 11-20, 21-30, 31-40, 41-50, 51 and moreWeibull

• Statistical analysis of NBI data to support criteria


Data Input Tools

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Conclusion• Data from RAP meetings being analyzed,

implemented in tools– Uncommon attributes– RAP identified criteria

• Back-casting process starting• Consequences text adjustment• On schedule to complete

– Letter Report September, 2013– Draft Report December, 2013– Compete March 2014

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Questions?

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Status of NCHRP 12-82 (1)

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