SEISMIC RELIABILITY-BASED DESIGN OF INELASTIC STRUCTURES WITH DIFFERENT VALUES OF THE POSTYIELDING STIFFNESS ISOLATED BY FPS

This work aims to evaluate the seismic reliability of nonlinear systems, considering both a hardening and softening post-yielding behavior, isolated by friction pendulum devices (FPS) for different values of the strength reduction factor. The isolated structure is described through an equivalent 2dof model, whereas, the FPS behavior is described by a velocity de-pendent model. An extensive parametric study is carried out encompassing a wide range of inelastic building properties considering different values of the post-yielding stiffness, differ-ent seismic intensity levels and considering the friction coefficient as a random variable. De-fined 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 yielding characteristics of the superstructures are consequently designed according to NTC08 for different values of the strength reduction factor. Incremental 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 corresponding limit states. Integrating the fragility curves with the seismic hazard curves 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 and proposed in order to provide useful design recommendations depending on both the strength reduction factors and post-yielding behavior