Seismic Fragility Analysis of Base-Isolated Structures Based on Response Surface Method

Base-isolated structures face a risk of damage under the action of earthquakes, and base isolation devices may be susceptible to damage during severe earthquakes. This study proposed an approach based on the response surface method to assess the base-isolated structures' seismic fragility and investigated the reliability and effectiveness of the base-isolation technique. Three performance levels and corresponding performance criteria for general base-isolated reinforced concrete structures were specified. The proposed seismic fragility assessment approach fully considered the uncertainty of the base-isolated structures and ground motions. Uncertainty parameters of the superstructure and base isolators were characterized, and parametric sensitivity analysis of the base-isolated structure was carried out. Moreover, the seismic fragility evaluation method of base-isolation systems was studied, and a simplified evaluation equation was introduced. The proposed response surface-based method's accuracy and efficiency were also compared with the Monte Carlo method. An actual project was taken as an example to illustrate the proposed approach. The failure probabilities of the base-isolated structure under various seismic intensity levels were calculated, and the seismic fragility curves were plotted. It indicated that the base-isolated structure could achieve the performance objectives of maintaining operation under minor earthquakes, guaranteeing life safety under moderate earthquakes, and preventing collapse under severe earthquakes. However, the seismic isolation bearings could still have large displacements under severe earthquakes. Furthermore, the seismic fragility analysis of the base-isolated and nonisolated structures was compared. It showed that the base isolation technique significantly reduced the damage probability of the superstructure under various intensity levels and effectively prevented the superstructure from entering a serious damage state. The proposed seismic fragility analysis approach and a large amount of computational data could provide a significant engineering application value for similar reinforced concrete structures and a reference value for the design of base-isolated structures.