SEISMIC RELIABILITY-BASED DESIGN OF PERFECTLY ELASTOPLASTIC STRUCTUTRES ISOLATED BY FPS

This paper deals with seismic reliability of nonlinear structural systems equipped with friction pendulum isolators (FPS). The isolated structures are described by employing an equivalent 2dof model characterized by a perfectly elastoplastic rule to account for the in-elastic response of the superstructure, whereas, the FPS behavior is described by a velocity dependent model. An extensive parametric study is carried out encompassing a wide 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 corresponding to life safety limit state for L’Aquila site (Italy) according to NTC08, the inelastic characteristics of the superstructures are designed as the ratio between the average elastic responses and increasing strength reduction factors. Incre-mental dynamic analyses (IDA) are developed to evaluate the seismic fragility curves of both the inelastic superstructure and the isolation level assuming different values of the corres-ponding limit states. Integrating the fragility curves with the seismic hazard curves related to L’Aquila site (Italy), the reliability curves of the equivalent inelastic base-isolated structural systems, with a design life of 50 years, are derived proposing seismic reliability-based design (SRBD) abacuses useful to define the FPS properties and superstructure properties.