Improving the earthquake resilience of isolated buildings with double concave curved surface sliders

The underlying concept of base isolation is the uncoupling of the horizontal building movement from ground motions using a flexible isolation layer made with either elastomeric or sliding bearings. Double Concave Curved Surface Sliders DCCSS are seismic isolators based on the pendulum principle. DCCSS isolators that do not include any mechanical elements that serve as end-stops coherently with European codes, for earthquakes stronger than the ultimate limit state ones, the inner slider runs on the edge of the sliding surfaces beyond their geometric displacement capacity (over-stroke regime) preserving the ability to support gravity loads. This paper focuses on the effects of the over-stroke displacement of DCCSS and of displacement restrainers on the seismic response of base isolated buildings considering a case study. At the first stage of testing, the numerical model of the bearings over-stroke behavior has been calibrated on an experimental displacement-controlled test carried out in this study, also considering few results available in the literature. Nonlinear static and dynamic analyses including inelastic superstructure and different basic isolation system models, with and without over-stroke effects and with and without strong end-stroke restraints, have been performed. The parametric analysis aims to estimate annual frequencies of exceeding the superstructure yielding limit when the isolators reach the maximum displacement varying end-stroke and over-stroke parameters.