SEISMIC FRAGILITY OF RC FRAME BUILDINGS DESIGNED FOR IS 1893:2016

Abstract

Since 1930, earthquake resistant design of buildings was developed to prevent collateral damage. Due to advancement in research, many changes were made in seismic design methods to address design related issues; Performance Based Design (PBD) is one such method being actively developed at present. Risk-targeted design is also an enhanced version of PBD which determines collapse probability of buildings. The present study identifies risk associated with buildings based on varying orientations of columns. Three buildings are considered in the study with their geometry and structural design so chosen as to assert the validity of a newly added clause on coupling of modes in IS 1893, 2016 (Part I). As per the clause 7.1 (vii), the difference in periods along principal directions should not be greater than 10%. Among the three buildings, the first one has same fundamental periods in both principal directions, whereas the second and third building has a difference of 12.0% and 3.5% in the fundamental period along principal directions, respectively. All buildings are designed as per revised IS 1893, 2016 and ductile detailing is done as per IS 13920, 2016. Coupling effect in buildings arises when there is swapping of energy between fundamental modes in principal directions. This effect can be observed by conducting linear dynamic analysis by comparing peak inter-storey drift ratio and peak displacement for uniaxial and biaxial excitations. Performance point and ductility of these buildings are also calculated by non-linear static analysis with reference of ASCE 41, 2013. Incremental dynamic analysis (IDA) is performed till collapse point, using far-field ground-motions as mentioned in FEMA P695 project, from PEER NGA database. IDA curves give median collapse spectral intensity with record to record variability. Fragility curves can be plotted using data obtained from IDA, is used to compute probability of collapse with respect to spectral accelerations. Effects of different orientation of columns on collapse probability of bisymmetric buildings are compared in this study.