GNGTS 2015 - Atti del 34° Convegno Nazionale

The distribution of the period of vibration ( T b ) of the buildings that are present in the valley in relations with their height shows a wide range of values (Fig. 3a). For this reason, it is not easy to select a unique value as representative for the dynamic behavior of a specific building. As indicated by Kham et al . (2006), the influence of the building on the local seismic response is higher in resonance condition between the building and the soil. An analysis of the distribution of the vibration period compared with the first resonance peak of the soil on which the buildings are founded, considering both the 1D (Varone et al. , 2014) and the 2D (Fig. 1 bottom) model, was carried out to evaluate the empirical relations that predict values of buildings fundamental frequencies close to the resonance frequency of the soil (Fig. 3b). As also this analysis did not allow the selecting of an empirical formulation adapt for this case study, in the following specific modeling of the dynamic behavior of each building of the Europarco neighbor should be performed. Conclusions. Starting from literature data on the geological setting of the Fosso di Vallerano valley in Rome and from the seismic background noise data collected during two measurement surveys, it was possible to obtain the geological and geotechnical model of the site. This profile was modelled to evaluate the propagation of seismic waves, the amplifications, the energy expected at the surface of the valley and the seismically induced strain in term of MSS. The distribution of the E ( x ) values along the geological cross-section (Fig. 1 top) and of the wave propagation maps (Fig. 1 middle) show that the shape of the valley and the thickness of the resonant body strongly influence these parameters. Moreover, the efficiency of the absorbing layer system as calibrated by Varone et al. (2014), was confirmed by the results obtained by the 2D numerical modeling. The analysis of the A( f ) x (Fig. 1 bottom) highlight a non-homogenous distribution of the resonance peaks along the valley; more in particular, a wide part of the section is characterized by a first resonance peak around 1Hz indeed the central and the eastern portion of the valley show a first resonance peak at a higher frequency value (around 3Hz). The distribution of the MSS shows that, in the heterogeneous model (Figs. 2a-2c), the highest shear strain values are concentrated in the recent alluvial body, in particular in the lithological unit 3; in the homogenous one (Figs. 2b-2d) the MMS values are lower respect to the ones resulted in the same location by considering a heterogeneous filling. The analysis of the period of vibration ( T b ) of the building did not allow to select an empirical formulation adapt for this case study, in fact the distribution of the obtained values with their height shows a wide range of variation. For this reason, it was not possible to chosen a unique value as representative of the dynamic behavior of the buildings and specific modelling are required to understand the dynamic behavior of each building of the Europarco neighbor. Other simulations are necessary to understand the role of the Site-City Interaction (SCI), i.e. the effect of the presence of the buildings built during the last decade on the propagation of the seismic waves, on the amplifications and on the energy expected at the surface level of the valley. Fig. 3 – Variation of the characteristic period (left) and of the resonance frequency (right) of the building in function of their height. On the right side is also indicated the resonance frequency characteristic of the soil calculated through the 1D and the 2D numerical modelling. 182 GNGTS 2015 S essione 2.2