GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 2.2 283 In the last two equations, DI 50 , DI 16 and DI 84 denote the variables representative of the damage state evaluated by considering the 50 th , 84 th and 16 th percentile of the selected records, respectively. Finally, to analyze the effect of the response spectra shapes on the fragility curves, these latter have been derived by using also the spectra proposed by the Italian code (NTC 2018). To this purpose the dispersion σ rtr has been assumed equal to the one derived from the accelerograms selected with REXEL. Results and discussion. Some of the results obtained by the proposed approach are herein reported in terms of fragility curves (Fig. 2) for the two structural typologies MUR1 and MUR2 defined in Table 1. In particular, they refer to the set of two-storey buildings, of MUR1 and MUR2, prone to the global overturning mechanism (Fig. 2a) and to the global overturning along openings (Fig. 2b). The fragility curves shown in red colour are evaluated by considering the spectral shapes derived by natural accelerograms (REXEL), while the ones in blue colour are evaluated by considering the smoothed spectra proposed by the Italian code (NTC 18). In this context, it is important to highlight that in the first case the record-to-record variability has been taken into account by means of the dispersion σ rtr directly evaluated on the natural records, while in the second case (smoothed spectra proposed by the Italian Code), the dispersion σ rtr has been set equal to the ones evaluated on natural records. It means that the blue and red curves have the same value of the record-to-record variability, but different model dispersions and different values of μ lnDIiIPGA . Despite this, the fragility curves appear similar to each other, and in particular those evaluated through the NTC18 spectra show to be more conservative. This suggests that, for the sake of simplicity, it is possible to obtain realistic Fig. 2. Fragility curves for the set of two-storey buildings, be parto of the two structural typologies MUR 1 and MUR 2: a) global overturning mechanism; b) global overturning along openings.