PSI - Issue 44

Giacomo Lazzerini et al. / Procedia Structural Integrity 44 (2023) 163–170 Giacomo Lazzerini et al. / Structural Integrity Procedia 00 (2022) 000–000

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system or class of buildings are mathematical functions that express the probability of reaching or exceeding different damage levels (DL i ) as a function of some ground motion intensity measure (IM). Fragility curves represent accurate, exhaustive and reliable predictive models for estimating the damage caused by earthquakes of variable intensity to a given building typology. Therefore, they play a key role in all studies concerning the prediction, prevention and mitigation of earthquake risk at the territorial scale. Considering that Italy has a relevant seismic risk and that many existing structures of the Italian building stock are not adequately designed against seismic actions, it is of primary importance to have reliable tools such as fragility curves to plan, schedule and implement targeted seismic risk reduction interventions. 2. Aim of the wok The aim of the work was the construction of new analytical fragility curves for a building typology that is very common in the Casentino area during the 1960s-1970s, where it represents the common ordinary typology in the expansion areas close to the historic centre. The investigated typology includes masonry multi-storey residential buildings, typically three- or four-storey buildings, which are characterized by floors well anchored to vertical walls, with perimeter wall thickness in the range 40 ÷ 50cm. Therefore, only the global behaviour was investigated, as the out of-plane collapse mechanisms of individual walls were blocked. Nonlinear static analysis was adopted as the methodology of analysis. The decision to investigate this building typology rise from previous vulnerability studies at the territorial scale about the Casentino area (Del Monte, 2017), a territorial area belonging to the province of Arezzo that includes 12 municipalities (Fig. 1a). Among the nine building typologies representative of the territory, the building typology covered by this work represents about 30% of the built-up area. For instance, two buildings belonging to the investigated typology are shown in Fig. 1b, c. (a) (b) (c)

Fig. 1: Examples of the investigated building: Building A (a), Building B (b), Building C (c). The fragility curves drawn in this work were derived using the analytical method (Calvi et al., 2006, Kassem et al., 2020, Maio & Tsionis, 2015) and developed from the probabilistic study of the capacity PGA obtained from the analyses of structural numerical models properly created to simulate the seismic behaviour of the investigated building typology. Following the most recent studies trend, in particular, Chieffo et al. (2019) and Milosevic et al. (2020), four damage levels were considered and damage thresholds were assumed to be coincident with the displacements corresponding to the four Limit States (Table 1) defined by the current Italian Building Code (NTC 2018). Table 1: Considered damage levels Damage Level (DL i ) Limit State Displacement on the bilinear curve DL1 SLS 2/3 D y DL2 DLS D y DL3 LSLS 3/4 D u DL4 CLS D u