GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.2 GNGTS 2023 The results, reported in terms of horizontal Peak Ground Acceleration (PGA) and amplification factor of Housner intensity at each control point, were compared with the simplified spectra for the subsoil classes identified in the control points, built in according to the Italian laws. The principal object of the comparison was the normalized elastic response spectra and, in particular, the related Housner intensity in two period classes, suitable to explain the horizontal seismic action on different types of buildings laying in the study area [Figure 2]. By reporting the Housner intensity factors calculated for the ground surface (in 1D and 2D modeling) and that associated with the bedrock (by NTC for subsoil class A), it was possible to assess the topographic effects contribution in the ground motion amplification [Figure 3]. The results of 2D numerical modeling confirm a fluctuating trend of amplification factors of the spectral intensity along the slope, even where the stratigraphy is uniform, as expected from studies on topographic effects of 80s and 90s (like Géli et al., 1988). For all other parameters, on the other hand, there is a statistically significant coincidence between 1D and 2D modeling. 1D modeling could result sufficient for the section, which moreover require fewer input parameters (and therefore less related uncertainties). Though, the most interesting evidence is the fact that the parameters of the simplified spectra provided by the Italian laws are almost always greater than those derived from both modeling. Simplified site modeling is therefore in any case the most precautionary approach for this analyzed site.