Computer Study of Redundancy of a Single Span Welded Steel Two-Girder Bridge

摘要

The AASHTO Highway Bridge Specifications penalize nonredundant steel members in bridges but present only rough and conservative guidelines for actually determining if a structure is redundant. The guidelines are based on the usual steel bridge design procedures, which in turn are based on oversimplified 2- dimensional idealizations of complex 3- dimensional structures. There is reason to believe that secondary members not specifically designed for vertical load actually contribute greatly to the redundancy of the bridge, providing a contribution to load redistribution capability not currently accounted for in design. The report describes a computer study investigating the hypothesis that a welded steel 2- girder bridge, commonly thought to be nonredundant, actually possesses significant load redistribution capability provided by such secondary member as the floor beams, cross frames, and bottom laterals. A finite element model of a real simple-span right 2- girder bridge is developed and subjected to dead load while imposing a full depth main girder crack at midspan. The results provide significant insights into the structural behavior and load redistribution mechanisms of the damaged bridge under dead load.