Preliminary Italian Maps of the Expected Annual Losses of Residential Code-Conforming Buildings

Abstract

The expected annual loss (EAL) is a metric often used to quantify the risk, including that related to seismic behavior of structures. It allows to combine the annual probability that the considered structure experiences any damage level, with the expected value of the consequences of such damages. In Italy, to promote seismic risk mitigation, a tax relief for retrofitting costs of existing buildings has been introduced. One of the two criteria adopted to demonstrate the improvement of the seismic performance of the structure after the retrofit is the comparison of (a simplified assessment of) the EAL before and after the retrofitting. In this context, it is interesting to quantify the EAL of code-conforming residential buildings of different structural typologies and supposed located in each Italian municipality. This kind of study descends from a recent Italian research project named RINTC – Rischio implicito delle strutture progettate secondo le NTC – that aims at the evaluation of the seismic reliability inherent to design according to the current Italian building code. Selecting some of the structures analyzed in the RINTC project, national maps of EAL for four code-conforming buildings are computed. Such structures are three- and six-storey reinforced concrete (RC) frame, infilled, buildings, and two- and three-storey unreinforced masonry (URM) buildings. The EALs are obtained combing the results of probabilistic seismic hazard analyses, performed in accordance with an authoritative source model for Italy, with the fragility functions derived for two performance (i.e., damage) levels, namely usability-preventing damage and global collapse. Results, following those of the RINTC project, generally show that: (i) EALs vary with the site and the considered structural typology; (ii) three-storey RC and two-storey URM are generally associated to the lowest EAL while the largest are often related to three-storey URM.