Influence of residual displacements on the design displacement of spherical friction-based isolation systems

This paper presents the results of an extensive parametric study aimed at investigating the influence of residual displacements on the design displacement of spherical friction-based isolation systems. Residual displacements may significantly jeopardize the displacement capacity of spherical friction-based isolation systems thus causing extensive damage or even triggering structural collapse. For that reason, they must be properly taken into account in the design. The study builds on the results of thousands of nonlinear response-time history analyses of SDOF systems, using almost one hundred ground motions pairs. Residual displacements arising from both individual earthquakes and sequences of seismic ground motions are considered. Based on regression analysis of results, a closed-form equation is derived to predict residual displacements of spherical friction-based isolation systems as a function of the main parameters governing their mechanical behavior. The proposed relationship is compared with state-of-the-art relationships and current seismic code provisions.