Bridge Rating Using System Reliability Assessment. I: Assessment and Verification by Load Testing

Condition assessment and safety verification of existing bridges and decisions as to whether a bridge requires posting currently are addressed through analysis, load testing, or a combination of these methods. The rating process is described in AASHTO’s Manual for Bridge Evaluation, which permits ratings to be determined by allowable stress, load factor, or load and resistance factor methods, the latter of which is keyed to AASHTO LRFD Bridge Design Specifications. These three rating methods may lead to differently rated capacities and posting limits for the same bridge, a situation that has serious implications with regard to public safety and the economic well-being of communities that may be affected by bridge postings or closures. This paper is the first of two papers that summarize a research program to develop improvements to the current bridge rating process using structural reliability methods. This paper appraises current bridge rating methods and summarizes a coordinated program of analysis and load testing of several bridges to support recommended improvements to the bridge rating process. The second paper presents the reliability basis for the recommended load rating and recommends specific improvements to current bridge rating methods in a format that is consistent with the load and resistance factor rating (LRFR) option in the Manual for Bridge Evaluation.