The paper deals with the seismic reliability of base-isolated structural systems
equipped with friction pendulum isolators (FPS) in order to provide useful design recommendations.
A two-degree-of-freedom model is adopted by 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 spectral displacement
corresponding to the isolated period has been chosen as intensity measure (IM).
The uncertainty in the seismic inputs as well as the friction coefficient at large velocity are
considered as random variables modeled through appropriate probability density functions.
Monte Carlo simulations are developed in order to evaluate the probabilities exceeding different
limit states related to both superstructure and isolation level defining the seismic fragility
curves. Finally, considering the seismic hazard curve related to an Italian site, closedform
expressions are derived with the aim to design the radius in plan of the friction pendulum
isolators in function of the expected reliability level
