Reliability analysis of two archetype RC buildings with hysteretic dampers

The manuscript deals with a study on the performance/reliability analysis of steel hysteretic dampers designed for the seismic retrofit of RC frame structures at the Basic Design Earthquake, BDE (characterized by a 10 % probability of being exceeded over the reference lifespan, VR) for higher hazard levels, represented by a Maximum Considered Earthquake, MCE, with either 5 %/VR or 2.5 %/VR exceedance probabilities. Indeed, seismic codes prescribe that anti-seismic devices designed to satisfy the performance requirements at the BDE must be able to resist earthquakes of higher intensity. Therefore, γ-factors amplifying the design displacement or force must be considered for the design of the device capacity. The objective of the study consists in evaluating the over-demand caused on the steel dampers incorporated in dissipative bracing systems when passing from the BDE to the two higher hazard levels, and comparing this over-demand to the values of the corresponding γ-factors proposed in current codes. Dampers with various ductility factors are considered to include the majority of current hysteretic devices. The amplification factors recommended in the codes for hysteretic dampers are shown to be not suitable for guaranteeing the damper reliability; moreover, a dependence of the reliability of the retrofitted structures upon the ductility of the damped braces is highlighted.