Seismic Analysis of Building with Underground Stories Considering Soil Structure Interaction

Current building codes lack explicit recommendations on how to simulate the seismic performance of high-rise buildings with multiple underground stories. Designers are typically basing their analyses on subjective engineering judgment and experience. Recent researches shows that seismic response of buildings with basement walls is a complicated phenomenon. This paper studies the seismic behaviour of reinforced concrete buildings with multiple underground stories. While current researches mainly aims at understanding the effects of soil structure interactions, this study has the ultimate goal of finding appropriate recommendations concerning the inclusion of underground stories in the model for seismic analysis. To achieve this objective, the methodology involves the computer modelling of building supported by raft foundation by two alternate approaches, namely, building frame with fixed supports, building frame with supports accounting for soil-flexibility using finite element software SAP 2000. Static analysis, modal analysis and time history analysis is done inorder to find the variation in natural period, bending moment s and deflections of structure by incorporating soil flexibility as compared to structures with conventional fixed base. The findings indicate that the seismic response of the building during severe shaking may be different than that predicted during the design process, and that the expected structural demands may not be as high as predicted because of the effects of soil structure interaction and basements. Present study does underscore that there is scope for rationalization in the IS codal provisions. Keywords—Soil Structure Interaction; Framed Structures with basement floors; Raft Foundation