Distortion-induced stresses in composite steel i-girder bridges

Repeated traffic loading assists distortion-induced fatigue cracks in the web gaps at connections between the steel girders and out-of-plane elements such as diaphragms and cross frames in the steel bridges. Unstiffened girder web gaps at the ends of transverse stiffeners, which also serve as diaphragm connection plates, are subjected to high local stresses during cyclic out-of-plane distortion. The out-of-plane distortion was mainly caused by relative girder deflection. This research investigates the effects of bridge parameters on the relative displacement between adjacent girders, vertical web gap stresses, and lateral load distribution factor. The parameters include the girder spacing, slab thickness, girder stiffness, and span length. By using finite element method, dual-level analyses using the global model and submodel were performed. The global model was used to study the relative displacement between adjacent girders and lateral load distribution factor, while the submodel was used for the critical web gap stress. From a parametric study, the rankings of bridge parameters that influence the relative displacement between adjacent girders, web gap stress and lateral load distribution factor are reported. For the web gap stress, the results showed that it is primarily dependent on bridge span length and web gap properties.