Anti-seismic devices are designed to meet performance criteria at the Life-Safety limit state and to resist earthquakes of higher intensity associated with the Non-Collapse limit state. To this end, current Seismic Codes prescribe γ-factors to amplify the design effect of the seismic action, ensuring adequate reliability margins. However, these factors vary across different Codes, and their effectiveness in guaranteeing structural reliability remains insufficiently investigated. This study examines the design of hysteretic dampers for the seismic retrofit of two reinforced concrete buildings (3 and 6 stories) following the provisions of the Italian Building Code for a return period of 475 years. A range of ductility levels is considered to reflect the diversity of hysteretic dampers available on the market. The seismic performance and the structural reliability of the retrofitted structures are evaluated under high intensity earthquakes by checking the absence of structural collapse and failure of the damper system. The time-history analyses consider seismic events with return periods of 975 and 1950 years. Findings reveal that the γ-factors prescribed in current Seismic Codes tend to be overly unconservative. Moreover, the results highlight a direct correlation between the reliability of retrofitted structures and the ductility of the damped braces.
Bruschi et al. (Thu,) studied this question.