Seismic response of bridges supported on shallow rock foundations considering SSI and pier column inelasticity

Traditionally, shallow spread footing type foundations are used for medium span bridges supported on rock strata. Such bridges are modeled with fixed supports and no Soil-Structure Interaction (SSI) is considered. The investigation presented herein utilized a substructuring technique and Finite Element Method (FEM) model for a medium span 4-span bridge designed for five different rock classes and subjected to an ensemble of actual ground motions. Non-linear behavior of reinforced concrete pier column was modeled for material and geometric non-linearity and incorporated in the overall analysis scheme by equivalent linear model while SSI was included through Winkler springs. The results of the study were evaluated to delineate the effect of SSI and pier column non-linearity on seismic response parameters of bridges founded on shallow foundations in rock strata. It was found that the SSI cannot be neglected in all cases of rock classes and input ground motions. Furthermore, pier column non-linearity influenced bridge displacement and base shear much more significantly than SSI and should not be ignored in the seismic modeling and analysis of these bridges.