NCHRP Report 782
presents a proposed Guideline for reliability-based bridge inspection practices and provides two case studies of the application of the proposed Guideline. The Guideline describes a methodology to develop a risk-based approach for determining the bridge inspection interval according to the requirements in the “Moving Ahead for Progress in the 21st Century Act (MAP-21)” legislation. The goal of the methodology is to improve the safety and reliability of bridges by focusing inspection efforts where most needed and optimizing the use of resources. The material in this report will be of immediate interest to bridge engineers.
The National Bridge Inspection Standards (NBIS) mandate the frequency and methods used for the safety inspection of highway bridges. The inspection intervals specified in the NBIS require routine inspections to be conducted every 24 months, and that interval may be extended to 4 years for bridges that meet certain criteria and are approved by FHWA. For bridges with fracture-critical elements, hands-on inspections are required every 2 years. The specified intervals are generally not based on performance of bridge materials or designs, but rather on experience from managing almost 600,000 bridges in the National Bridge Inventory.
These inspection intervals are applied to the entire bridge inventory, but they may not be appropriate for all bridges. For example, recently constructed bridges typically experience few problems during their first decade of service and those problems are typically minor. Under the present requirements, these bridges must have the same inspection frequency and intensity as a 50-year-old bridge that is reaching the end of its service life. In the case of bridges with fracture-critical elements, newer bridges with improved fabrication processes and designs that mitigate the effects of fatigue are inspected on the same interval and to the same intensity as older bridges that do not share these characteristics.
A more rational approach to determining appropriate inspection practices for bridges would consider the structure type, age, condition, importance, environment, loading, prior problems, and other characteristics of the bridge. There is a growing consensus that these inspection practices should meet two goals: (1) improving the safety and reliability of bridges and (2) optimizing resources for bridge inspection. These goals can be accomplished through the application of reliability theory.
Research was performed under NCHRP Projects 12-82 and NCHRP 12-82(01) by the University of Missouri to develop a proposed bridge inspection practice for consideration for adoption by AASHTO. The methodology developed is based on rational methods to ensure bridge safety, serviceability, and effective use of resources.
The report includes two parts: Part I— Proposed Guideline for Reliability-Based Bridge Inspection Practices and Part II— Research Report that documents the entire research effort.