Reliability validation of multigirder steel bridges designed by LRFD

The reliability index is examined for steel girder highway bridges designed by AASHTO load and resistance factor design (LRFD) Strength I limit state. The reliability analysis is based on the extensive stochastic finite element method (SFEM). The SFEM takes advantages of the conventional advanced first-order second-moment in that it considers the mechanic connection between the critical member and other members in the whole structure. The bridges are modeled as grillage beam systems. Basic design variables include sectional properties and various dead and live loads. The results obtained in noncomposite steel bridges indicate that the reliability index is very sensitive to the lateral distribution of live loads. Consequently, a simplified method is used in the reliability analysis of composite steel bridges. This simplified method can avoid the complex computation in SFEM yet achieve good accuracy. Due to overestimating the lateral distribution of live loads, the Strength I limit state in AASHTO LRFD specifications results in a conservative design for flexure but not for shear.