Seismic Performance Evaluation of R c-Framed Buildings - An Approach To Torsionally Asymmetric Buildings

Abstract

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 strengths may cause serious damage in structural systems. This research quantifies the performance of the torsionally balanced and torsionally unbalanced buildings also called as symmetric and asymmetric buildings by subjecting to pushover analysis. The buildings have un-symmetrical distribution of stiffness in storeys. In this paper the effort is made to study the effect of eccentricity between centre of mass (CM) and centre of stiffness (CR) and the effect of stiffness of infill walls on the performance of the buildings. The performance of the buildings is assessed as per the procedure prescribed in ATC-40 and FEMA-356. Four building models are considered for study, which are constructed on hard soil in seismic zone Ш of India (as per IS: 1893-2002(9)), one symmetric and 3 asymmetric in stiffness distribution. Infills were modeled using equivalent strut approach. Static analysis (for gravity and lateral loads) and non-linear pushover analysis (assigning the hinge properties to beams and column sections) were performed. It is concluded that the performance of the models in which the stiffness of walls considered is found better when compared with the models in which the stiffness of walls ignored. And with increase in eccentricity, the performance point of the structure will be more but due to increase in stiffness, structure may fail in brittleness.