Seismic reliability-based design of double sliding devices for softening structures

This study deals with seismic reliability-based design (SRBD) relationships in terms of behavior factors and displacement demands for softening structures equipped with double friction pendulum system (DFPS) bearings. An equivalent 3dof system having a softening 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 superstructures 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 performed to evaluate the seismic fragility and the seismic reliability of these systems. Finally, seismic reliability-based linear and multi-linear regressions relating the displacement ductility demand and the behavior factors for the softening superstructures together with seismic reliability-based design (SRBD) curves for the two surfaces of the double sliding devices are described.