Author : Halkude S.A., Kalyanshetti M.G. and Barelikar S.M.

In the conventional method of design of raft foundation flexibility of soil mass is ignored which is likely to affect the performance of structure. In the proposed study an attempt is made to understand the effect of soil flexibility on the performance of building frames resting on raft foundation. The purpose of this study is to describe and investigate different approaches of considering soil flexibility in the soil structure interaction analysis (SSI) with regard to the response in the superstructure. The present study is focused on SSI analysis of symmetrical space frame of 2 bay in both x and y direction, 2 storey (2X2X2), 2 bays in both direction, 5 storey (2X2X5) and 2 bay in both direction, 8 storey (2X2X8) resting on raft foundation with fixed base and flexible base. Three types of soil i.e. Hard, Medium Hard and Soft Soil are used for the SSI study. Dynamic analysis is carried out using the Response Spectra of IS: 1893-2002. The soil flexibility is incorporated in the analysis using Winkler approach (spring model) and elastic continuum approach (FEM model). SAP-2000 is used for developing these models. The effect of SSI on various structural parameters i.e. natural time period, base shear, roof displacement, beam moment and column moment are studied and discussed. The comparison is made between the approaches of SSI modeling i.e. Winkler approach (spring model) and elastic continuum approach (FEM model). The study reveals that the SSI significantly affects the response of the structure. Elastic continuum approach (FEM model) has proved to be the effective approach for consideration of elastic continuum beneath foundation.

Keywords: Soil Structure Interaction, Seismic Response, Response Spectrum, Raft Footing, Finite Element Method, Elastic Continuum, Winkler Method, SAP-2000.

Article published in International Journal of Current  Engineering  and Technology, Vol.4,No.3 (June- 2014)