Comparative seismic fragility of torsionally irregular RC buildings designed using Indian and European codes

Abstract

Presence of irregularities in building tends to increase its seismic vulnerability. To improve their performance, many current seismic design codes specify larger demand and more stringent design requirements for torsionally irregular buildings, as compared to regular buildings. The current Indian seismic design code (IS 1893 Part 1), however, provides design guidelines that are essentially applicable to only regular buildings. With this view, the objective of the present study is to evaluate the behaviour and capacity at collapse of mid-rise RC frame-shear wall buildings, with and without torsional irregularity, designed according to current IS 1893 (Part 1) and BS EN 1998-1 codes. For this purpose, three-dimensional building models are subjected to bi-directional incremental dynamic analyses (BIDA), using a set of far-field ground motion records. To account for the cyclic deterioration of stiffness and strength, the non-linear behaviour of beams is modelled using an experimentally calibrated lumped plasticity model, while the columns and shear-walls are modelled using fibre-hinge models (ETABS-CSI, 2016) duly calibrated with the experimental results available in literature. Results of the BIDA are used to assess the collapse capacity, and for developing seismic fragility curves according to the FEMA P695 methodology. The results are compared and discussed, with particular emphasis on the adequacy and limitations of the design provisions and recommendations in the two codes, in context of torsionally irregular buildings.