Seismic performance evaluation of base-isolated nuclear power plant reactor building considering aging effect of isolation device

The base isolation (BI) device is widely used for reducing seismic energy transmitted to the upper part of the structures. The rubber property of lead rubber bearing (LRB) BI devices degrades with time and environmental conditions, affecting the controlling performance of BI devices. This study investigates the degradation of capacity of base-isolated nuclear power plant (BI-NPP) considering the aging of rubber material used in the LRB BI device. An NPP reactor building with BI devices is numerically modeled. To capture the nonlinear behavior of the BI device, a bilinear hysteretic model is considered. Assuming different ages, the nonlinear incremental dynamic analysis is conducted using a set of 25 earthquakes and the seismic outcomes are evaluated through fragility analysis. The seismic capacity is extracted from the fragility parameters in terms of High Confidence of Low Probability of Failure (HCLPF) capacity. The outcome shows that the capacity degraded remarkably up to 21% for 100 years of service life. Finally, the seismic capacity degradation model is proposed through the investigation, which will be helpful to evaluate the capacity of the BI-NPP structure for any instant of time.