PSI - Issue 44

Valentina Buonocunto et al. / Procedia Structural Integrity 44 (2023) 67–74 Valentina Buonocunto et al. / Structural Integrity Procedia 00 (2022) 000–000

71

5

Once the i -th building was generated, seismic performance was assessed through nonlinear static analysis according to the N2 method (Fajfar, 2000).

Fig. 2. 3D equivalent frame model of randomly generated URM building

In order to derive analytical fragility curves, multiple damage states (DSs) were directly defined on the pushover capacity curve of the URM building, as follows: • DS1 at 70% of the maximum base shear ( V b,max ) on the rising branch of the capacity curve; • DS2 at V b,max ; • DS3 at 20% base shear drop (i.e. 0.8 V b,max ); • DS4 at 50% base shear drop (i.e. 0.5 V b,max ); • DS5 at the ultimate displacement. The occurrence of each damage state is highlighted by different coloured dots in Figure 3, where they are identified on a typical pushover curve of a URM building. For each model analysed, the capacity was determined with respect to the five damage states and compared to increasing levels of seismic demand. Assuming the peak ground acceleration (PGA) as intensity measure, the frequency of exceeding each prescribed DS was evaluated, leading to a set of fragility points under varying PGA. Empirical fragility data sets associated with each DS were thus fitted through a lognormal fragility function, which was then converted according to the MARS model (Masi et al. 2021).

Fig. 3. Definition of damage states on building pushover curve