Influence of the strength reduction factor on the seismic reliability of structures with FPS considering intermediate PGA/PGV ratios

This paper deals with seismic reliability of nonlinear structural systems equipped with friction pendulum isolators (FPS), subjected to different natural seismic records with intermediate PGA/PGV ratios. The isolated system is described by a 2DOF system and the FPS behavior is described by employing a velocity dependent model. The friction coefficient at large velocity is considered as a random variable. Employing a set of natural seismic records having intermediate PGA/PGV ratios 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 by evaluating the ratio between the average elastic responses and increasing strength reduction factors. Incremental Dynamic Analyses (IDA) are developed to evaluate the seismic fragility of both the superstructure and the isolation system assuming different values of the corresponding limit states. Integrating the fragility curves with the seismic hazard curve related to L'Aquila site (Italy), the reliability curves of the inelastic base-isolated structural systems, with a design life of 50 years, are derived.