Inelastic load distribution in multi-girder composite bridges

To accurately assess the ultimate load capacity of concrete slab-steel girder bridges, the effects of concrete nonlinearity and steel yielding on the truck load distribution in simply supported composite bridges are investigated using the nonlinear finite element (FE) method. In this study, fifty cases are analyzed to investigate the effect of the aforementioned parameters as well as the effects of other parameters including longitudinal and transversal truck position, number of loaded lanes (2–4), bridge length (12–20 m) and width (8–16 m), number of girders (3–6), girder spacing (2–3.75 m), and slab thickness (175–275 mm). The moment in each girder, based on the nonlinear FE analysis, is used to obtain its Load Distribution Factor (LDF) at different load levels up to failure and is compared with the corresponding elastic LDF according to AASHTO LRFD specifications. The results show from zero to 54% increase in the internal girder LDF (average 32%), and from zero to 29% decrease in the external girder LDF (average 17%) as the bridge traverses from the elastic to the ultimate state. This redistribution can be advantageously used when evaluating the load carrying capacity of existing bridges.