Bridge Rating Using System Reliability Assessment. II: Improvements to Bridge Rating Practices

The current bridge-rating process described in AASHTO Manual for Bridge Evaluation, First Edition permits ratings to be determined by allowable stress, load factor, or load and resistance factor methods. These three rating methods may lead to different 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 second of two papers that summarize a research program to develop improvements to the bridge-rating process by using structural reliability methods. The first paper provided background on the research program and summarized a coordinated program of load testing and analysis to support the reliability assessment leading to the recommended improvements. This second paper presents the reliability basis for the recommended load rating, develops methods that closely couple the rating process to the results of in situ inspection and evaluation, 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 AASHTO Manual for Bridge Evaluation.