Effect of Soil–Structure Interaction on Seismic Isolated Bridges

Abstract

The role of soil–structure interaction (SSI) on the response of seismically isolated bridges is studied. A generic bilinear hysteretic model is utilized to model the isolation system. The behavior of the pier is assumed to be linear and the foundation system is modeled with frequency-dependent springs and dashpots. Two bridge systems were considered, one representative of short stiff highway overpass systems and another representative of tall flexible multispan highway bridges. Nonlinear time history analyses were employed with two sets of seismic motions; one containing 20 far-field accelerograms and one with 20 near-fault accelerograms. The results from these comprehensive numerical analyses show that soil–structure interaction causes higher isolation system drifts as well as, in many cases, higher pier shears when compared to the fixed-pier bridges (no SSI).