Improved bridge capacity rating methods based on system reliability assessment

Bridge condition assessment and decisions as to whether posting is required are addressed in the United States, through analysis, load testing, or a combination of these methods. The analytical methods specified in the AASHTO Manual of Bridge Evaluation (2008), are the most commonly used methods for bridge rating. However, the load and resistance factor rating method in this Manual was developed based on statistical databases that describe the capacity of individual bridge girders; system effects were included only indirectly and approximately through girder distribution factors. While component-based design of new bridges provides adequate safety at reasonable cost, component-based evaluation of existing bridges may be unduly conservative and result in unnecessary repairing or posting. This paper summarizes a recently-completed research program that investigated bridge safety at the system level using reliability-based approach and presents new perspectives on the level of conservatism furnished by the current generation of reliability-based bridge rating procedures.