This work is concerned with the reliability-based characterization of base-isolated systems for any sort of structural configurations. In particular, base-isolated buildings under uncertain excitation are considered. A probabilistic approach is adopted for considering the variability of future excitations. Isolation elements composed by lead rubber bearings are used in the present formulation. The biaxial hysteretic behavior of the isolation elements is calibrated with experimental data in order to obtain a more accurate and realistic representation of these sort of devices.

 The reliability-based characterization of the isolated structural system is defined in terms of the isolator deformations, the maximum inter-story drift and the superstructure absolute accelerations. First excursion probabilities are used as measures of the system reliability. Three example problems are presented in order to illustrate the usefulness and applicability in the future of the proposed characterization of base-isolated buildings.