Computer study of redundancy of a single span welded steel two-girder bridge, Interim Report, March 1986, 72p.

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. These guidelines are based on the usual steel bridge design procedures, which in turn are based on oversimplified 2-dimensional idealizations of 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. This 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 members 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 and midspan. The results provide significant insights into the structural behavior and load redistribution mechanisms of the damaged bridge under dead load.