PSI - Issue 44

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Carpanese Pietro et al. / Procedia Structural Integrity 44 (2023) 1752–1759 Carpanese Pietro et al./ Structural Integrity Procedia 00 (2022) 000–000

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The curves obtained for each building in the database were then post-processed according to the methodology proposed by Donà et al. 2021, in order to obtain complete fragility sets for each macro-typology, both for the as-built

configuration and for the retrofit options analyzed (Follador et al. 2021). Fig. 1 shows some examples of fragility sets for the Pre-1919 epoch. 3. Seismic risk maps and expected benefit

Once the fragility curves for each intervention strategy have been defined, they can be implemented in the IRMA platform (Borzi et al. 2021), which processes seismic hazard, vulnerability, and exposure data in Italy, in order to produce maps of seismic damage and risk, both conditional (i.e., for a specific return period), and unconditional (for an observation time window). As far as exposure is concerned, IRMA relies on the data provided by the Italian national census ISTAT (2011), which gives information about the number of buildings, their total area, and their typology at a municipality level. In these elaborations, direct economic losses have been assessed. In IRMA, the reconstruction cost is assumed to be 1350 €/m2, and the loss is computed as a function of building damage, i.e., each damage state is associated with a percentage of loss (2% for DS1, 10% for DS2, 30% for DS3, 60% for DS4 and 100% for DS5) (Di Ludovico et al. 2017a, b). The economic losses have been calculated firstly for the as-built condition, and then for all the different retrofit possibilities that each building macro-typology allows (as described in 2.1), assuming that they are applied across the entire residential building stock. The expected benefit in a given time window has been calculated. Benefit is defined as the difference between the economic losses for a scenario where all buildings are in the as-built configuration and the case where an intervention strategy is implemented extensively at national level. Fig. 2 shows an example of this computation for each municipality and for a time window of 50 years, considering all the buildings in Italy belonging to the Pre-1919 epoch, where the benefit is expressed as the reduction of economic losses (%) between the as-built configuration and all the possible retrofit strategies. The maps show both individual interventions and combined ones. It should be noticed that similar outcomes can be observed both when considering particular combinations of interventions but also through single interventions that have a greater impact (for example, the MSN1+TR map is very similar to that relating to MSN2). In addition, in some cases the combination of lighter interventions leads to benefits very similar to those obtained with heavier interventions (for example, MSN1+FLR reaches the same level of benefit achieved by the heavier intervention MSN2 + FLR). These considerations can be significant when planning mitigation actions on a territorial scale. However, since the benefit is greatly influenced by exposure, the results can also be proposed in terms of normalized benefit, calculated as the ratio between the benefit in each municipality and the area of buildings that belong to it (therefore, a ratio between benefit and exposure). Fig. 3 shows the maps of normalized benefit (€/m 2 ) for a time window of 50 years, at provincial level, referring to Pre-1919 and 1919-1945 buildings and to the individual interventions associated to these epochs. Correspondingly, Fig. 4 shows the same type of maps, this time considering buildings belonging to 1946-1960 and 1961-1980, where different interventions can be proposed. As expected, the normalized benefit is less for more recent epochs, as greater improvements are achieved when applied to more vulnerable buildings. These maps can also be used to define risk mitigation strategies, in order to decide on which types of building act with greater priority, as well as with which intervention.