Effective base isolation combining low-friction curved surface sliders and hysteretic gap dampers

The re-centering capability represents a fundamental property of any effective isolation system. Indeed, a potential residual displacement after an earthquake, besides affecting the serviceability of the construction, may also result in increased peak displacements during aftershocks and future events. In curved surface sliders (CSSs), energy dissipation and re-centering capability are two competing aspects influenced by the friction coefficient and the state of lubrication of the sliding pad. On the one hand, the large energy dissipation capability of high friction CSSs contributes to mitigate the displacement demand during strong events but negatively affects the recentering behavior. On the other hand, low-friction CSSs exhibit a better re-centering behavior, but are expected to undergo large displacements that, in turn, imply large dimensions in plan and pose problems of possible pounding between adjacent buildings and damage of nonstructural elements, lifelines and utilities crossing the isolation joint. The present study proposes an efficient base-isolation system that combines low-friction CSSs with hysteretic gap dampers. The latter device introduces supplemental energy dissipation only when the displacement of the isolation system exceeds a threshold or initial gap while not being engaged otherwise. The mechanical properties of the gap damper are designed to provide a target energy dissipation such that the displacement demand of low-friction CSSs can be kept to the same level as that of high-friction CSSs. A parametric study comprising a series of nonlinear response history analyses and different CSS characteristics demonstrates that the supplemental dissipative mechanism of the gap damper does not impair the re-centering capability of the CSS isolators. These outcomes are additionally validated by comparing numerical simulations of a 3D base-isolated case-study frame with shake-table test results. The proposed base-isolation system efficiently combines satisfactory energy dissipation, which reduces the displacement demand, with high re-centering capability resulting in negligible residual displacements.