Soil Structure Interaction of Bridges for Seismic Analysis

Keywords: Soil structure interaction.  Bridges.  Ground motion.  Spatial variation.  Local soil conditions.  Spectrum compatible time history. ATC-32.  Acceleration  response spectra.  Bridge foundations.  Spread footings.  Gravity caission.  Drilled shafts.  Pile groups. Substructuring.  

Abstract: This report documents the current state-of-practice in soil-stricture interaction analyses for seismic design of bridges. It covers several relevant areas such as ground motion aspects, various issues on soil-structure interaction for typical foundations and methods of substructuring to reduce the number of degrees of freedom for foundation elements.
The ground motion topic includes seismic hazard analyses, seismic performance criteria, spectrum compatible time history, spatial variation of ground motions, effects of local soil condition, and the recent ATC-32 recommendations on standard ARS (Acceleration Response Spectrum) design criteria. The soil-structure interaction area discusses modeling of foundation stiffness and damping for spread footing, gravity caisson, large diameter drilled shaft, and pile group. The concept of substructuring technique is described fully. The technique offers two approaches: one based on kinematic soilstructure interaction and the other based on inertia interaction. Both are intended to reduce the number of degrees of freedom for the foundation to be used in the global bridge analyses.