Soil Structure Interaction Effect on Seismic Response of R.C. Frames with Isolated Footing

TLDR: In this article, the effect of soil flexibility on the performance of building frame is investigated, and two soil structure interaction modes are considered for the analysis; one is replacing soil by spring of equivalent stiffness (Discrete Support) and second by considering the whole soil mass (Elastic Continuum).

Abstract: The seismic response of a structure is greatly influenced by Soil Structure Interaction (SSI). In this study the effect of soil flexibility on the performance of building frame is investigated. Two SSI modes are considered for the analysis; one is replacing soil by spring of equivalent stiffness (Discrete Support) and second by considering the whole soil mass (Elastic Continuum). Symmetric space frames resting on isolated footing of configurations 2 bay 2 storey (2X2X2), 2 bay 5 storey (2X2X5) and 2 bay 8 storey (2X2X8) are considered with fixed base and flexible base. The spring model is developed by using stiffness equation along all 6 DOF and elastic continuum model is developed by Finite Element Method using SAP-2000. For SSI study three types of soil are considered i.e. Hard, Medium Hard and Soft Soil. The dynamic analysis is carried out using Response Spectrum, given in IS1893-2002. The influence of soil structure interaction on various structural parameters i.e. natural time period, base shear, roof displacement, beam moment and column moment are presented. The study reveals that the SSI significantly affects on the response of the structure. Finite Element Method has proved to be the effective method for consideration of elastic continuum below foundation.