Evaluating the use of variable curvature frictional isolators to mitigate the adverse effects of internal lateral impacts

Abstract

Under high magnitude ground motions, excessive base displacement can generate internal lateral impacts between inner sliders and restraining rims of frictional isolators. This study aims to evaluate the use of variable curvature frictional isolators to mitigate the adverse effects of these internal impacts. One specific geometry of the sliding surface was studied, obtained by revolving an ellipse around a vertical axis. Due to the shape of the sliding surface, the pendular force transmitted by the bearing exhibits a smooth hardening behavior. A physical model for dynamic analysis of base-isolated structures equipped with variable curvature frictional bearings is presented. This numerical model accounts for effects such as large deformation, sticking, uplift, and lateral and vertical impact behavior. The impact parameters of the physical model were calibrated using a Finite Element Model subjected to dynamic loads. A three-dimensional model of a base-isolated structure was developed to characterize the dynamic behavior of an adaptive passive isolation system under different base displacement demands. Finally, a nonlinear reinforced concrete frame equipped with isolators with spherical or elliptical sliding surfaces was examined to determine the average reduction in the Engineering Demand Parameters affected by internal impacts. On average, reductions of 44%, 11%, 8%, and 6% in the maximum response of the base shear, first inter-story drift, second inter-story drift, and third inter-story drift are obtained by replacing classical Friction Pendulum System (FPS) devices with variable curvature isolators.