GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 2.2 259 Tab. 1 - Values of ductility indicators averaged on the different normalized slenderness. Increase ductility demand Seismic Sequences typology M1 δ M2 δ M3 δ Natural – Totality (1) 2.44% 10.52% 4.44% Natural – Selection (2) 6.16% 23.23% 10.57% Artificial (3) 23.26% 41.73% 23.99% Overall weighted averages (1,3) 16.32% 31.33% 17.47% In general, the indicators increase as the normalized slenderness increase for the artificial sequences, however the trend is less clear for the natural sequences. With the aim to give an overall mean value, average values are calculated by mediating the values obtained for each different normalized slenderness (Table 1). In the Table 1, in order to underline what has been previously asserted, the indicators for a selection of 10 natural sequences, with after-shocks with comparable intensity to the main-shock ones, have also been reported. Generally, the effect of the seismic sequences can be significantly variable on the basis of the sequences and the indicators considered. It has to be underlined that with this approach the seismic hazard is considered the same as the one of the single main-event; only the seismic vulnerability has considered to be increased. Conclusions. In this work the effect of the seismic sequences has been studied on steel X-CBFs for one floor industrial buildings. First, a whole industrial building has been evaluated. Then, the study has been focused on a single XCBFs, calibrated on experimental cyclical test. Three different average indicators have been formulated. The final average values give an estimate of the increase of ductility demand, by passing from single main events to repeated ground shakings. It shows a great variability depending on the sequence typology and the indicator considered. By assuming M1 δ and M3 δ as the most significative parameters, increments of 16.3% and 17.5% respectively have been calculated. b) a) Fig. 3 - a) Enlargement of elastic response spectrum through the scale factor η seq = 1.2; b) Seismic hazard map of the italian national territory; areas subjected to the enlargement of the elastic response spectrum are those characterized by PGA ≥ 0.2 g.