Effect of ageing on the seismic risk of RC wall–frame buildings under sequential earthquakes and consequences for insurance premiums

In India, a large stock of RC wall–frame buildings with deficient structural wall plan density (SWPD) is potentially vulnerable to combined ageing-induced deterioration and repeated seismic excitation. The primary objective of the present study is to evaluate the seismic risk of such building stock and to analytically derive the insurance parameters for the risk management, considering both ageing effects and sequential ground motion (GM) records. Three levels of corrosion rate (CR) or corrosion deterioration are considered, representing severe ageing, moderate ageing, and no ageing. A performance-based framework is adopted in which nonlinear response-history analyses are used to develop seismic fragility and vulnerability functions. These functions are subsequently integrated with a site-specific seismic hazard curve to estimate annual seismic damage rate and seismic financial risk. The results show that the combined influence of corrosion deterioration and sequential GMs leads to a substantial increase in annual seismic damage rate, with the maximum amplification observed at near-collapse damage state. The financial risk results further show that the sequential GM records increase absolute financial loss with the increase in corrosion rate; however, its relative (multiplicative) impact across different hazard levels is highest for no ageing effect (CR=0%). Finally, using a novel approach, the insurance parameters are determined, and the effect of corrosion-induced deterioration on the annual premium rate is quantified. Overall, the findings demonstrate the importance of accounting for the coupled effects of corrosion deterioration and sequential GMs in the seismic risk evaluation of RC wall–frame building stock and provide quantitative support for risk-informed mitigation strategies and insurance decision-making.