Hardening structures isolated by double sliding devices: Seismic reliability-based design approach

This study deals with seismic reliability-based design (SRBD) relationships in terms of behavior factors and displacement demands for hardening structures equipped with double friction pendu-lum system (DFPS) bearings. An equivalent 3dof system having a hardening post-yield slope is adopted to describe the superstructure behavior, whereas velocity-dependent laws are assumed to model the responses of the two surfaces of the DFPS. The yielding characteristics of the super-structures are defined for increasing behavior factors in compliance with the seismic hazard of L’Aquila site (Italy) and with NTC18 assuming a lifetime of 50 years. Considering several natural seismic records and building properties under the hypothesis of modelling the friction coefficients of the two surfaces of the DFPS as random variables, incremental dynamic analyses are per-formed to evaluate the seismic fragility and the seismic reliability of these systems. Finally, seis-mic reliability-based linear regressions relating the displacement ductility demand and the behav-ior factors for the hardening superstructures together with seismic reliability-based design (SRBD) curves for the two surfaces of the double sliding devices are described.