The effect of superstructure properties on the re-centering capability of Friction Pendulum (PS) isolator

The re-centering capability after the seismic excitation is one of the fundamental properties of a seismic isolation system. This study examines the effects of superstructure properties on the re-centering capability of the Friction Pendulum (FP) isolator. To this end, a comprehensive parametric study is conducted using a two-degree-of-freedom (2DOF) model that accounts for the nonlinear behavior of the superstructure and isolator. This study evaluates the re-centering capability of the FP isolator by calculating the ratio of residual displacement (dres) to the maximum displacement (dmax). The effect of superstructure properties, including strength reduction ratio R, fundamental vibration period Ts, post-yield stiffness ratio αs, superstructure damping ratio ξs, and the ratio of superstructure mass to total mass of the system γm on the dres/dmax ratios is thoroughly analyzed. The findings suggest that while estimating the residual displacement of isolation systems, it is important to consider the impact of superstructure parameters. An analytical equation is proposed to predict dres/dmax ratio based on effective superstructure and isolator parameters.