IDA-based fragility assessment of an RC shear wall building under repeated earthquakes

Seismic design and assessment procedures generally represent earthquake demand using single-event ground-motion scenarios and may therefore overlook the cumulative damage caused by successive earthquakes. This study investigates the nonlinear seismic response and vulnerability of a seven-story reinforced-concrete (RC) shear wall building designed according to the Turkish Building Earthquake Code (TBEC-2018) under single-event and repeated-earthquake excitations. A three-dimensional nonlinear model was developed in ETABS, and eight bidirectional earthquake-record pairs were spectrally matched to the site-specific design spectrum. Incremental dynamic analyses were performed for the first-earthquake, second-earthquake, and combined first–second earthquake scenarios. In total, 855 bidirectional nonlinear time-history analyses were conducted, comprising 311 first-earthquake, 299 second-earthquake, and 245 combined-sequence analyses. The maximum inter-story drift ratio (MIDR) was adopted as the engineering demand parameter, considering the Immediate Occupancy, Life Safety, and Collapse Prevention drift limits of 0.5%, 1.0%, and 2.0%, respectively. At the selected reference intensity of Sa(T 1 , 5%) = 0.5 g, the combined sequences increased roof-displacement demands by approximately 5–15% in several records; however, the drift demands remained within the Immediate Occupancy range and well below the Life Safety and Collapse Prevention limits. The results indicate that repeated shaking has a limited influence at the selected reference intensity but becomes more significant in the strongly nonlinear range by reducing the remaining deformation capacity and collapse-prevention margin. The results evaluated through fragility curves indicate that the potential damage-amplifying effects of repeated earthquakes, particularly under higher-intensity shaking, should not be overlooked in earthquake-resistant structural design.