Empirical verification of soil-structure interaction provisions in building codes

While seismic design practice in the areas of ground motion assessment and structural response analysis has undergone rapid evolution in recent years, SSI provisions in many U.S. building codes have not changed since 1978, and in other codes such as the Uniform Building Code (ICBO, 1997), SSI is ignored altogether. This situation can be improved with seismic performance data which provides insight into SSI processes and helps establish confidence in SSI analysis procedures. In this paper, current SSI provisions in two U.S. building codes (BSSC, 1995 and ATC, 1978) are examined relative to a database of "observed" SSI effects evaluated from system identification analyses on strong motion recordings from 53 building sites. The code provisions are found to provide a reasonable basis for analysis of inertial interaction effects in a gross sense (i.e. when the results are averaged over a large number of case histories), but limitations for several classes of structures and foundations are identified.