A proposal for the calibration of the Italian seismic action in accordance with a reliability-based design procedure

In Italy the current seismic design standards for new and existing constructions relies on Uniform-Hazard Approach ( UHA ), assigning fixed hazard-exceedance probabilities to different Limit States ( LSs ). However, this approach leads to non-uniform seismic risk, since failure probabilities vary across a territory depending on local seismic hazard conditions. To cover this gap, this study proposes a reliability-based procedure for calibrating the seismic action of constructions, consistent with the probabilistic framework of SAC FEMA and the Risk-Targeted Approach ( RTA ). In accordance with this procedure, target reliability indexes and the corresponding reliability factors are proposed by referring to the current MPS-04 seismic hazard model. To this scope exceedance probabilities for different LSs and Consequence Classes ( CCs ) are defined, and the seismic hazard function parameters are optimized in a log–log space. Assuming the annual failure probability of 2 × 10 − 4 provided by FEMA, average target reliability factors of 2.11 for the Ultimate Limit State ( ULS ) and 1.0 for the Serviceability Limit State ( SLS ) are obtained for the Italian territory. Based on these values, mean target reliability indexes are then derived as functions of the LS and CC . The results obtained clearly show that, coherently with the UHA , the Expected Annual Losses ( EALs ) and reliability indexes vary significantly across Italy, indicating a non-uniform risk distribution. Conversely, the reliability-based procedure achieves uniform seismic risk by introducing a site-specific modification factor to the MPS-04 seismic action. The reliability factors derived according to the proposed design procedure may be readily implemented in the design code to calibrate a seismic action ensuring a uniform seismic risk across the Italian territory.