SEISMIC RELIABILITY ASSESSMENT OF EQUIVALENT PERFECTLY ELASTOPLASTIC BASE-ISOLATED STRUCTURES

This paper deals with seismic reliability of nonlinear structural systems equipped with friction pendulum isolators (FPS). The FPS behaviour is described by a bilinear model, dependent on ve-locity, while superstructures are described by a 2dof model with a perfectly elastoplastic beha-viour. A parametric study is carried out encompassing a range of elastic and inelastic building properties, different seismic intensity levels and considering the friction coefficient as a random variable. Employing a set of natural seismic records and scaled to the seismic intensity corres-ponding to life safety limit state for L’Aquila site (Italy) according to NTC08, the inelastic cha-racteristics of the superstructures are designed as the ratio between the average elastic responses and increasing strength reduction factors. Using Incremental Dynamic Analyses (IDA) and as-suming different values of the limit states for the isolation level and for the superstructure, the seismic fragility curves are evaluated. The reliability curves of the inelastic base-isolated structur-al systems, with a design life of 50 years, are derived integrating the fragility curves with the seismic hazard curve related to L’Aquila site (Italy). The reliability curves are seismic reliability-based design (SRBD) abacuses, useful to define the FPS properties and superstructure properties.