SEISMIC RELIABILITY OF BASE-ISOLATED STRUCTURAL SYSTEMS THROUGH FPS

The paper deals with the seismic reliability of structural systems equipped with friction pendulum isolators (FPS). The behavior of these systems is analyzed by employing a two-degree-of-freedom model accounting for the superstructure flexibility, whereas the FPS isolator behaviour is described by adopting a widespread model which considers the variation of the friction coefficient with the velocity. The uncertainty in the seismic inputs is taken into account by employing a set of synthetic records, obtained through Monte Carlo simulations within the power spectral density method, with different characteristics depending on the soil dynamic parameters, and scaled to increasing intensity levels. The friction coefficient at large velocity is considered as random variable modeled through a uniform probability density function. Incremental dynamic analyses are developed in order to evaluate the probabilities exceeding different limit states related to both superstructure and isolation level defining the seismic fragility curves through an extensive parametric study carried out for different structural system properties. Finally, considering the seismic hazard curves related to L'Aquila site (Italy), the seismic reliability of the superstructure systems is evaluated as well as seismic reliability-based design (SRBD) abacuses are derived with the aim to design the radius in plan of the friction pendulum isolators in function of the structural system properties and the selected reliability level.