SEISMIC PERFORMANCE OF IRREGULAR BUILDINGS

Abstract

This paper deals with the effects of presence of irregularities in buildings on their seismic performance. The objective of the project is to carry out response spectrum analysis (RSA) of two reinforced concrete (RC) framed building models, one with a square shaped plan having symmetry in plan about the orthogonal axes and the other with an L-shaped plan which is asymmetric in plan, considering vertical mass irregularity in each floor. Mass irregularity is considered in each floor of the building models by increasing the value of live load on each floor by 50%, 100%, 150% and 200% and the effect of such increase in live load is studied. Plan area and translational stiffness of square shaped and L-shaped plan building models is taken to be same in the present study. The cross-sectional dimension of outer column (at origin in plan) in every storey is also kept same for both the building models and comparison of the analysis results is done for such columns. Various analysis results such as base shear, forces in the outer column elements considered, displacement of joints at the intersection of outer column elements considered and beam elements in every storey, etc. are obtained using SAP 2000 version 20.0.0 and the variation of these results is studied by introducing mass irregularity in each floor one by one. These results are compared for both types of building models considered. It is observed that base shear and joint displacements are more for the L-shaped plan building than that for the square shaped plan building. This led to a conclusion that the square shaped plan building performs better than the L shaped plan building during a seismic event. It is also observed that presence of mass irregularity increases the seismic response parameters of the building.