SESMIC RESPONSE OF R.C. BUILDING FRAMES WITH STRAP FOOTING CONSIDERING SOIL STRUCTURE INTERACTION

Abstract

In the conventional design practice the buildings are assumed to be fixed at their bases even though they are supported on flexible media (soil) which will change the structural behaviour. Thus to evaluate the realistic behavior of structure the soil structure interaction (SSI) effect shall be incorporated in the analysis. In the present study two SSI models are considered for the analysis; one is replacing soil by spring of equivalent stiffness (Discrete Support) and second by considering the whole soil mass beneath footing (Elastic Continuum). The support flexibility causes differential settlements and rotations of footings which lead to redistribution of forces/moments in the members of the structure. It possible to control these effects by providing the strap beam in the footing. Therefore in the present study an attempt is also made to investigate the influence of strap footing to control the SSI effect. The study is carried on 3D building frame of different story heights supported on soft soil. The seismic analysis is carried out using equivalent static method as per IS 1893-2002. The influence of SSI on various seismic parameters and the flexural parameters are presented. The changes in all these parameters due to provision of strap footing is studied in order to evaluate it’s effectiveness in controlling the SSI effect. The study reveals that the SSI significantly alters the forces/ moments in the members of the structure which is possible to control effectively by providing the strap footing.