LAUSR

Abstract This study proposes seismic reliability-based design relationships in terms of behavior factors and displacement demands for softening and hardening structures equipped with double concave sliding bearings (i.e., DFPS). An equivalent 3dof system is adopted, that is characterized by a hardening or softening post-yield slope, representative of the superstructure response, and by velocity-dependent laws to model the frictional responses of the two surfaces of the DFPS. The yielding characteristics of the superstructures are defined for increasing behavior factors, provided by the codes, in compliance with the seismic hazard of L'Aquila (Italian site) and with the life safety limit state as provided by NTC18. Considering several natural ground motions and different elastic and inelastic structural properties under the hypothesis of modelling the friction coefficients of the two surfaces of the DFPS as random variables, incremental dynamic analyses are developed to assess the seismic fragility. From the convolution integral of the fragility curves with the seismic hazard curves related to L'Aquila (Italian site), assuming a lifetime of 50 years, the corresponding reliability curves are computed. Precisely, seismic reliability-based linear and multi-linear regressions relating the displacement ductility demand to the behavior factors for the softening and hardening superstructures together with seismic reliability-based design (SRBD) curves for the two surfaces of the double concave sliding bearings are provided as the design relationships.