Seismic modeling and performance evaluation of seismically isolated building considering large strain effects under near-fault earthquakes

Lead rubber bearings (LRBs) have been widely used in seismically isolated buildings to mitigate earthquake damages in highly earthquake-prone regions. The deformation of the LRBs has been generally recognized to conform to the bilinear model under moderate shear deformation. However, when the bearings are loaded with large strain deformation, LRBs exhibit a significant increase in stiffness and strength due to the hardening characteristics of the rubber. Nevertheless, the dilemma in engineering practice is that most of the existing LRB models in design software cannot capture complex hardening behaviors under large strain loadings. Furthermore, although some LRB models can consider the large strain effects, they require many calibrated parameters. For this reason, a concise generalized Bouc–Wen model was proposed (hereinafter referred to as BoucWenG model) in this work, which can improve the aforementioned limitations of the traditional LRB models while retaining the favorable features of the Bouc–Wen model. The detailed features of the BoucWenG model were introduced first. Then, the generalized model was verified using the experimental results of LRBs with different sizes under cyclic large strain loadings. Furthermore, considering the large strain effects, we examined the seismic performance of the base isolation system using two comparative isolated reinforced concrete frame buildings, in which the base isolation bearings were simulated by the traditional Bouc–Wen and the proposed BoucWenG models. Next, we conducted seismic fragility analyses of these two isolated buildings through incremental dynamic analysis, in which the near-fault (NF) ground motions characterized by large-amplitude velocity pulse were also considered. The comparison results reveal that the proposed BoucWenG model can well represent the large strain hardening and strength degradation properties of LRBs. Furthermore, the dynamic responses of the superstructure and the isolation system significantly tend to vary when the large strain effects of the bearings are considered under strong earthquakes. The traditional LRB model, which ignores the large strain effects, may highly overestimate the shear deformation of the isolation layer and lead to poorer-than-expected seismic isolation effects for the superstructure, especially under strong NF earthquakes.