GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.2 GNGTS 2023 Comparison Between Seismic Amplification Factors From Ntc18 And Those Obtained By Data From Italian Seismic Microzonation Studies E. Paolucci 1 , A. Tanzini 2 , D. Albarello 2 1 CNR-IGAG, Montelibretti (Roma), Italia. 2 Dipartimento di Scienze Fisiche, della Terra e dell'Ambiente, Università degli Studi di Siena, Italia. Given their ease of use, the simplified approaches based on the use of some seismic “proxies” and contained in the most common building code provisions (e.g., EN 1998-1 Eurocode 8, 2004) are the most widespread methods in the professional activity to estimate the ground-motion amplification due to the local seismo-stratigraphical features. In Italy, this kind of approach is also present in the actual national building code (NTC18; Ministero delle Infrastrutture e dei Trasporti, 2018). As is now well known, this procedure assigns an acceleration response spectrum through the estimation of the soil class of the investigated site, which is identified by the values of two proxies, that is the seismic bedrock depth H (i.e., the layer with Vs ≥ 800 m/s) and the time average Vs down to H ( VS H ) or to 30 m depth ( VS 30 ), if H is lower or higher than 30 m respectively. The objects of this study are the seismic Amplification Factors (AFs) referred to each soil class, defined as: , (1) = 1 2 ∫ 1 2 ∫ where Sa represents the acceleration response spectrum of soil classes B, C, D and E respectively, while Sb is the response spectrum of soil class A. T 1 and T 2 represent the extremes of the considered period interval: in particular, three values of AF are considered corresponding to three intervals 0.1–0.5 s, 0.4–0.8 s and 0.7–1.1 s. These values were computed by Pergalani et al. (2020) for all the 8091 Italian municipalities and considering the response spectra referred to the Italian Seismic Hazard Map ( https://esse1-gis.mi.ingv.it/mps04_eng.jsp) relative to the ground motion expected to be exceeded with a probability equal to 10% in 50 years. The aim of this work is to test the effectiveness of these AF estimates (hereafter AF_NTC18) verifying if these values are enough conservative with respect to those obtained by 1D numerical simulations carried out in the same sites. To perform this analysis, the methodology proposed by Paolucci et al. (2020) was considered: using this approach, it is possible to evaluate if the number of excesses from AF_NTC18 is significant from a statistical point of view or it can be considered as a random fluctuation. A first attempt in this direction was done by Tanzini et al. (2021) considering as comparison dataset the AF values obtained by the level 3 Seismic Microzonation studies of 25 municipalities damaged by the 2016–2017 seismic sequence in Central Italy. Since these authors showed that NTC18 may not provide enough conservative estimates for soil class B in the period interval 0.1-0.5 s, it was considered appropriate to explore this kind of comparison taking into account a larger AF dataset. For this purpose, outcomes from the “National Map of Expected Values of Amplification Factors”