Seismic Fragility Analysis of Open Ground Storey RC Frames

Abstract

Seismic fragility functions are essential for the performance-based seismic design of structures. The current study focuses on common forms of vertically irregular RC buildings, known as open ground story buildings, where irregularity lies at the ground storey. OGS buildings are characterized by accumulation of large lateral displacement at the ground storey. This is due to drastic reduction in relative stiffness of the ground storey compared to the upper stories, a phenomenon known as soft storey effect. In the present study, this issue is investigated by carrying out fragility analysis of low- to mid-rise masonry infill RC frames with varying bays and storeys. Fragility curves are derived using nonlinear dynamic time history analysis carried on three and five-storey OGS and bare frame RC buildings by using method suggested by Cornell and Baker. Nonlinear dynamic analyses of building subjected to a number of ground motions, each scaled-up for different PGA, are carried out to estimate the inter-storey drift ratio. It is observed from fragility analyses that OGS frames with increasing number of bay and storey configurations, vulnerability to damage also increases. Fragility Function Parameters calculated using incremental dynamic analysis and maximum likelihood estimate are found to be close.