Seismic Vulnerability of Code Compliant RC Frame Building with Unreinforced Masonry Infill Walls

Unreinforced masonry (URM) infill walls in Reinforced concrete (RC) buildings are normally designed as non-structural elements. However, in the past, the post-earthquake response of the RC frame building showed that URM infill walls increase the strength and stiffness of the RC frame buildings. Further, it is also observed that URM helped to prevent the disastrous destruction by acting as a structural member in RC frame. In the present study, the performance assessment of a four-storey URM infill RC frame with different infill configurations, namely bare and Open Ground Storey (OGS) is done using fragility analyses. Nonlinear masonry material is modelled as the equitant three strut model in ETABS. Nonlinear static pushover analysis is applied for the analysis of the configured RC frames. The probability of damage states is determined by firstly converting pushover curves into capacity curves and accordingly, performance-point values of Spectral acceleration and Spectral displacement for seismic demand Zone-V (Elastic Response Spectra as per IS 1893:2016) using the capacity-spectrum method (ATC-40) are determined. The fragility function used is an approximation of the continuous to discrete distribution. Fragility curves and mean damage matrix are derived to compare performance with each other. From the vulnerability analyses, it is observed that the OGS framed RC building performs better as compared to the bare frame.