A parametic study on the effect of soil-structure interaction on seismic response of MDOF and equivalent SDOF systems

[Truncated abstract] Even though extensive researches have been conducted on Soil-Structure Interaction (SSI) since 1960s, there are several aspects of the complex phenomenon of SSI that have not been addressed thoroughly. The complex behavior of SSI together with uncertainties in soil and structure parameters, and in ground motions result in a significant controversy over the effect of SSI on structural response in both elastic and inelastic states. Recent studies considered SSI in inelastic response analysis are mainly based on idealized structural models of single-degree-of-freedom (SDOF) systems. However, due to neglecting the effects of higher modes, the number of building stories and lateral strength and stiffness distributions along the height of structures, an SDOF system might not be able to realistically capture the SSI effects on the inelastic responses of real buildings. The primary objective of this research is to advance, through extensive parametric study and analytical research, knowledge on the effects of SSI on elastic and inelastic responses of Multi-Degree-Of-Freedom (MDOF) systems, and to develop optimization techniques for optimum seismic design of elastic and inelastic shear buildings taking into consideration the SSI effects. Firstly, the study addresses the effect of SSI on elastic and inelastic response of MDOF and its equivalent SDOF systems. The adequacy of equivalent SDOF model to estimate strength and ductility demand of multi-storey soil-structure systems are intensively investigated. It is concluded that using the common E-SDOF systems for estimating the strength demands of average and slender MDOF systems when SSI effect is significant can lead to very un-conservative results. Secondly, the effect of structural property distribution on strength demand and ductility (strength) reduction factor of MDOF fixed-base and soil-structure systems has been investigated.