Seismic retrofit cost model for Italian masonry residential buildings to support territorial-scale risk analysis

Over the last 50 years, earthquakes forced the Italian Government to pay emergency, recovery and reconstruction costs amounting to 180 billion euros, i.e., about 3.6 billion euros per year. These figures underline the poor seismic resilience of Italy and therefore the need for sustainable risk mitigation plans at national level. Within this context, this study aims to provide a seismic retrofit cost model for Italian unreinforced masonry (URM) residential buildings, to support territorial-scale risk analysis. To this end, well-established intervention techniques, suitable for being analyzed on a large scale, were selected. These interventions include strengthening of masonry walls, stiffening and anchoring of floors, improving the wall system connection, and their possible combinations. First, for each of the selected interventions, the related cost items (obtained via a work-breakdown-structure procedure) were identified. Second, their unit cost was either retrieved from Italian price lists or estimated according to market analysis ad hoc conducted. Third, a quantity-survey-method approach was implemented to a set of 445 URM buildings to estimate the retrofit costs per square meter (€/m2) of investigated retrofit interventions. Lastly, based on the estimated cost of retrofitting of these buildings, parametric cost models were developed to inform seismic risk analyses at various territorial scales, depending on the available building information (i.e., exposure data). The cost models here developed and proposed can be used to support the design of cost-effective seismic mitigation measures, i.e., to identify retrofit solutions that are technically effective but also economically sustainable at large territorial scale.