A physical model for dynamic analysis of structures equipped with variable curvature frictional isolators

Abstract

During high magnitude ground motions, the internal lateral impact between inner sliders of frictional isolators and restraining rims of sliding surfaces may occur, jeopardizing the benefits of seismic isolation. In this study, a variable curvature friction isolator that exhibits a smooth-hardening behavior at large lateral displacements is evaluated as an alternative to mitigate the adverse effects of internal impacts. The geometry of the sliding surface is obtained by revolving a plane ellipse around a vertical axis. The pendular force transmitted by the isolator increases in stiffness as the device is laterally deformed. This research presents a physical model of variable curvature frictional isolators valuable for analyzing the three-dimensional dynamic response of structures equipped with variable curvature devices. The suggested physical model is capable of accounting for essential modeling features such as large deformations, P-∆ effects, sticking and sliding phases, uplift, kinematics constraints, and the lateral impact behavior. The presented force-displacement relationship of the frictional bearing with smooth-hardening behavior was validated using a Finite Element Model (FEM) under static and dynamic loads. An accurate representation of the coupling between the horizontal components of the pendular and frictional forces transmitted by the isolator is achieved by employing the physical model. The impact parameters of the physical model were calibrated to match the dynamics response of the FEM subjected to unidirectional and bidirectional ground motion inputs. Finally, a comparative example of a base-isolated three-dimensional structure is presented to show how the dynamic response is affected when variable curvature bearings form the isolation system.