Study on Seismic Induced Torsion of a Multi-Storied Building with Different Irregularities with and Without Base Isolation System

At present scenario many buildings are asymmetric in plan and/or in elevation based on the distribution of mass and stiffness along each storey throughout the height of the building. Most recent earthquakes have shown that the irregular distribution of mass, stiffness and strength may cause serious damage in structural systems. This study compares the behavior of buildings with and without base isolation system which are subjected to earthquakes. The buildings have un-symmetrical distribution of stiffness in storeys. In this study the effort is made to compare the behavior of building with and without base isolation when torsion is induced in the structures due to earthquake. Four building models are considered for study, which are constructed in seismic zone-III and zone-IV of India (as per IS: 1893-2002). All four models are un-symmetric in various parameters such as Re-entrant corner, mass irregularity, vertical geometric irregularity and stiffness irregularity. It is concluded that the performance of the models in which the base isolation is provided is found better when compared with the models in which the base isolation is not provided. Analysis results shows reduction in base shear and story acceleration values for base isolated building. The displacement, story drift and time period of base isolated structure is increased as compared to fixed base structure. The vertical geometric irregular and re-entrant corner structures are the most affected during earthquake actions.