Evaluation of seismic response of inelastic structures considering soil-structure interaction

Structural deformations and soil displacements arising out of ground shaking are intertwined. This interplay is termed as seismic soil-structure interaction (SSI). Over last few decades, the conventionally perceived beneficial nature of SSI has been challenged with evidences of damaged sites from various earthquakes. This paper evaluates effects of SSI on seismic response of hardening single degree of freedom systems located in diverse geologies. The assessment is performed using substructure approach in terms of inelastic force reduction factor such that structure attains certain ductility levels. It is observed that soil-structure systems can afford a lesser reduction in design seismic forces compared to fixed-base structures. Components of total displacement arising out of structural deformation, footing translation and footing rotation are also evaluated. With increase in SSI effects, contribution of structural deformation is found to decline sharply. Footing rotation is observed to be very significant in structure-soil systems with larger SSI effects. The soil-structure system is modelled using a discrete physical model which enables inelastic response to be obtained in time domain while considering frequency dependence of impedance functions.