UC Berkeley

Recent improvements in seismological source modeling, analysis of travel path effects, and characterization of local site effects on strong shaking have led to significant advances in both code-based and more advanced procedures for evaluating seismic demand for structural design. A missing link, however, has been an improved and empirically verified treatment of soil-structure interaction (SSI) effects on both the strong motions transmitted to structures and the structural response to these motions. This paper describes analysis procedures and system identification techniques for evaluating inertial SSI effects on seismic structural response. The analysis procedures are similar to provisions in some building codes but incorporate more rationally the influence of site conditions and the foundation embedment, flexibility, and shape on foundation impedance. Implementation of analysis procedures and system identification techniques is illustrated using a building shaken during the 1994 Northridge earthquake. The analysis procedures predict the observed SSI effects accurately. A companion paper applies these analyses to empirically evaluate SSI effects using available strong motion data from a broad range of sites and then develops general conclusions regarding SSI effects on seismic structural excitation and response.