Identification of Soil-Structure Systems

Abstract

Structures interact with soil under seismic excitations through both inertial and kinematic effects. These soil-structure interaction (SSI) effects are often significant and system identification methods can be used to characterize and quantify them. However, system identification of soil-structure systems is fraught with difficulties. SSI renders it virtually impossible to directly measure the earthquake input motions for a soil-structure system due to kinematic interaction effects, which is the term used for denoting the differences between the soil motions at the free field and the foundation, in the absence of superstructure mass. Moreover, because of disproportional distribution of damping in a soil-structure system, normal modes are no longer able to decompose the overall system’s equations of motion. Additionally, while some structures may remain linearly elastic even under high levels of vibration, soil behaves nonlinearly even under weak ground motions. Through work spanning the past decade various new methods of system identification have been devised appropriate for soil-structure systems—some of which, incidentally, are by the authors of the present article. This chapter provides an overview of the said techniques along with several application examples.