Phenomenological modeling of fiber-reinforced elastomeric isolators at multiple lateral deformation levels

Unbonded fiber-reinforced elastomeric isolators (FREIs) are a cost-effective seismic isolation technology that uses lightweight fiber-fabric reinforcement and forgoes the attachment plates connecting the isolators to the supports. These devices exhibit a complex nonlinear mechanical behavior under lateral deformation, which has typically been represented by uniaxial phenomenological models. In this paper, a new model, called Pivot Bouc–Wen model, is proposed to address the shortcomings of existing numerical models and obtain a better prediction of the response over the whole range of motion. The model has been formulated with the objective of providing (a) improved interpretability of the model parameters, (b) adequate energy dissipation prediction at multiple deformation levels, and (c) stable response at large deformations. The model combines a nonlinear elastic spring and a Bouc–Wen element with a modified pivot hysteresis rule to capture the lateral response of the isolators at different deformation amplitudes. Initial values for the model parameters are recommended based on existing analytical formulations of the quasi-static lateral response of FREIs and data corresponding to 36 cyclic tests from 12 different experimental programs. The proposed and existing models are compared in their ability to predict the lateral cyclic test results from a previous experimental study. The models are further compared via response history analyses of idealized one, two, three and four-story base-isolated shear buildings subjected to 30 ground motions at different intensity levels. The results highlight the importance of capturing the hysteretic response of the isolators at multiple deformation levels and not only at the maximum expected displacement.