Reliability of systems equipped with viscous dampers with variable properties

Viscous dampers are energy dissipation devices widely employed for the seismic control of structures. The performance of systems equipped with viscous dampers has been extensively analyzed by employing deterministic approaches. However, these approaches ne-glect the response dispersion due to the uncertainties in the input as well as in the structural system properties. Some recent works highlighted the important role of these uncertainties in the seismic performance of systems with linear or nonlinear viscous dampers. The present study focuses on the uncertainty in the damper properties and it aims at evaluating its influ-ence on the probabilistic response of the damped system. In particular, the variability of the damper properties is assumed to be constrained by the tolerances allowed in qualification and production control tests. A preliminary study on the damper response is carried out to relate the constitutive damper characteristics to the parameters controlled in the experi-mental tests and to evaluate the consequences of damper parameter variations on the dissipa-tion properties of the device. In the subsequent part of the study, the response hazard curves, providing the relation between the values of the response parameters of interest and the rele-vant yearly exceedance probability, are evaluated. In the analyses, a simplified structural sys-tem is considered, and the Subset Simulation (SS) algorithm is employed together with the Markov Chain Monte Carlo method to achieve a good estimate of small probabilities of exceedance. A sensitivity analysis, considering the expected variations in the damper proper-ties, is finally carried out by employing the Augmented SS method to study the influence of the device acceptance ranges on the hazard curves.