Probabilistic seismic demand analysis of buildings equipped with nonlinear Viscous dampers

Viscous dampers are energy dissipation devices widely employed for the seismic control of new and existing building frames. To date, the performance of systems equipped with viscous dampers has been extensively analyzed by employing deterministic approaches neglecting the response dispersion due to the site seismic hazard condition and the record-to-record variability effects. This paper analyzes the probabilistic seismic performance of building frames equipped with viscous dampers by highlighting the influence of damper properties. In particular, a probabilistic methodology based on response hazard curves is employed to evaluate the effect of the damper nonlinearity, measured by the damper exponent, on the performance of structural and non-structural components of building frames, as described by the response hazard curves of the relevant engineering demand parameters. A case study consisting of a steel frame equipped with nonlinear viscous dampers is considered and the performance variations due to changes in the damper nonlinearity level are evaluated by considering design scenarios corresponding to dampers having different exponents designed to provide the same deterministic performance. Both response statistics at different seismic intensity levels and demand hazard curves for the monitored engineering parameters are employed as performance measures. It is shown that the damper nonlinearity strongly affects the seismic performance and different trends are observed for the various demand parameters of interest. A comparison with code provisions shows that further investigation is necessary to provide more reliable design formulas for the dampers accounting for their nonlinearity level.