Standard requirements for the recentring capability of curved surface sliders

In order to obtain a full serviceability of base isolated structures after earthquakes, the curved surfaces sliders based isolation systems should have a sufficient recentring capability to avoid large residual displacements and their accumulation. The residual displacement estimations are expressed as function of the isolator properties (effective radius and friction coefficient) and of the characteristics of the ground motion (maximum displacement). The current seismic codes use different empirical approaches about the recentring capability requirements and for the expected residual displacements. Moreover, their evaluation can be done with sufficient accuracy only through complex numerical nonlinear time-history analysis. In this paper, the recentring capability of Curved Surface Sliders is discussed on the base of the main results of recent experimental studies and on the codes requirements. Moreover, a simple design tool for the estimation of the permanent residual displacement of the curved surface isolation systems is proposed as function only of the isolators properties.