Seismic reliability of yielding base-isolated structures

The aim of this work is to estimate the seismic reliability of base-isolated systems equipped with friction pendulum devices (FPS) and characterized by an intermediate isolation degree value considering both isolation devices and superstructures with a nonlinear behavior. The systems are modelled by means of 2dof nonlinear models considering both an hardening and softening behavior for the superstructure and a velocity-dependent rule for the FPS. The systems are designed according to NTC08 considering different structural parameters, an intermediate isolation degree value and a set of natural seismic record scaled to the seismic intensity corresponding to life safety limit state for L’Aquila (Italy). The yielding proprieties of the systems are valuated considering different values of the strength reduction factor and of the post-yielding slope. Then, incremental dynamic analysis are performed in order to evaluate the seismic fragility of both isolation level and inelastic superstructures. Considering the seismic hazard curve relative to L’Aquila site and using the convolution integral, the reliability curves of the yielding baseisolated systems, with an intermediate isolation degree value and a design life of 50 years, are derived.