Total displacement of Curved Surface Sliders during an earthquake: effect of coexisting non-seismic actions

The restoring capability is a fundamental function of any effective isolation system, required to prevent accrual of displacements that may limit the capability to withstand aftershocks and future earthquakes. For systems endowed with good restoring capability the displacement capacity is determined according to Eurocode 8 by adding to the design seismic displacement the non-seismic offset induced from permanent and thermal actions and long-term deformations of the structure. However it is noted that the design provisions of EC8 were developed for bilinear hysteretic systems and their validity for nonlinear isolation systems with high damping capacity has not yet been evaluated. The study investigates the re-centering capability of Curved Surface Sliders (CSSs) and the influence of the non-seismic offset on the displacements induced from the design earthquake. Nonlinear Time-History Response analyses are conducted, considering five non-seismic offset displacements combined with a wide range of device characteristics covering the current design practice. Twenty-four natural ground motion time histories are selected from a database and classified in terms of the predominant period of the quake and the level of impulsivity. Based on the results of the analyses, an improved formulation of the Eurocode’s re-centering criterion for Curved Surface Sliders is eventually proposed.