Residential code-conforming structural seismic risk maps for Italy

RINTC – Rischio Implicito delle strutture progettate secondo le NTC is an Italian research project aiming at the evaluation of the seismic reliability inherent to design according to the current Italian building code. Within the project, different fixed-base residential and industrial structures typologies, as well as some base-isolated reinforced concrete buildings were addressed. The structures were located in three Italian sites characterized by different levels of seismic hazard. For each designed, modelled, and analyzed building, the seismic reliability, in term of annual failure rate, was computed. Based on these results, the aim of the study discussed in the paper is to derive national seismic risk maps for Italy in an ideal scenario where all the existing (residential) buildings would be code-conforming, either fixed-base or base-isolated. The analyses are performed at the municipality scale, combining the structural fragility functions with alternative models of probabilistic seismic hazard for Italy, and including exposure in terms of typological composition of the existing building stock. Results, presented in the form of maps of structural failure rates, generally show that: (i) despite the same return period of design seismic intensity over the country, failure rates greatly vary with the increasing hazard of the sites (generalizing one of the main outcomes of the RINTC project), (ii) the alternative hazard models produce limited variations of the failure rates, especially when global collapse is considered.