Abstract

One of the most effective strategies for protecting buildings against high-magnitude earthquakes is the use of frictional seismic isolators. However, during extreme seismic events, large base displacements may induce internal impacts, leading to a significant increase in ductility demand. To mitigate these adverse effects, a novel isolator (i.e., the Lateral Impact Resilient Double Concave Friction Pendulum (LIR-DCFP) bearing) has been developed. This device limits impact forces and provides additional energy dissipation, enhancing seismic performance. The LIR-DCFP bearing incorporates an enhanced inner slider composed of two rigid bodies (top and bottom sliders) in mutual contact, forming a high-friction planar interface with an internal gap that permits relative displacement. Due to this configuration, the isolator exhibits two sliding phases: a low-friction phase and a high-friction phase activated by internal impacts. This study investigates the optimal relationship between the low- and high-friction coefficients that minimizes a key Engineering Demand Parameter (EDP): the ductility demand of the superstructure. A comprehensive parametric analysis was conducted on 6048 base-isolated systems, accounting for variability in both superstructure and isolation system properties. Seismic input uncertainty was incorporated using multiple sets of recorded ground motions matched to the conditional spectra of a site in Riverside, California. For each configuration, the optimal frictional design was identified by minimizing the geometric mean of the EDP. Results indicate that an optimal frictional configuration can reduce maximum ductility demand by up to 38%. The benefits are most pronounced for relatively stiff superstructures with a significant portion of the total mass concentrated at the base. Additionally, longer isolation periods require lower optimal high-friction coefficients, while higher low-friction coefficients need a more precise selection of relatively small high-friction values.