Seismic fragility and risk assessment of masonry infilled low ductile RC frames retrofitted with BRBs

Masonry infilled reinforced concrete (RC) frames are a widely adopted construction typology worldwide, including areas with moderate to high seismicity.A large percentage of such structures were built before the implementation of modern seismic design codes, are vulnerable to seismic shaking, and need retrofitting.To this end, buckling-restrained braces (BRBs) have been proven to be an effective retrofit strategy for improving the seismic performance and safety of such structures.However, limited considerations have been made on the influence of masonry infills on the effectiveness of the retrofitting.Masonry infills are often overlooked in the seismic analysis and design of RC frames due to their brittle nature.However, recent research has shown that their strength and stiffness can significantly influence the seismic response of buildings structures, affecting seismic fragility and risk estimates.The present study investigates the impact of masonry infills on the seismic fragility and risk of lowductile RC frames retrofitted with BRBs.A three-story, three-bay, low-ductile RC frame is selected for case study purposes.Finite element (FE) models for various structural configurations, i.e., Bare Frame, Infilled Frame, BRB-retrofitted Bare Frame, and BRBretrofitted Infilled Frame, are developed in OpenSees.Nonlinear static and dynamic analyses are performed to evaluate the seismic performance of the case study structures.A cloud analysis-based approach, with a suite of ground motion records, is used to account for the record-to-record variability and develop seismic fragility curves.The study uses the average spectral acceleration as the intensity measure (IM) to account for the time period elongation resulting from the masonry infills and frame damage during seismic shaking.A seismic hazard curve is developed for the considered IM, and seismic risk estimates are derived.The results provide insights into the interaction between masonry infills and BRB retrofits, highlighting their impact on seismic fragility and risk.