GNGTS 2015 - Atti del 34° Convegno Nazionale

and the best results were obtained considering a damping variation up to Q min -1 ≈ 2 (� ����� ξ ����� =1.0) defined by a linear function in the heterogeneous case (five layers with piecewise constant damping) and linear as well as square root function in the continuous case. This theoretical approach was already experienced by considering a homogeneous elastic medium and an absorbing lateral layered boundary, but it was not yet tested for heterogeneous deposits, as in the here considered case study. As reported by Varone et al. (2014) a new numerical solution was designed according to the parameters used by Semblat et al. (2011) but introducing two horizontal and homogeneous sub-layers and considering impedance contrasts from 1.4 up to 12.5 to monitoring the efficiency of the lateral absorbing layers assuming different hypothesis. The obtained results demonstrated that also for the heterogeneous domains, the best solution for an efficient attenuation of the spurious waves reflected at the model artificial boundaries consists in 5 absorbing layers with damping linearly varying; this optimal solution is considered for the 2D numerical modelling here presented. Structural and dynamic characterization of the buildings. The Fosso di Vallerano valley is a portion of Rome characterized from the last decades by a strong urbanization. The urban agglomerate is mainly composed by residential buildings, characterized by rectangular or square geometry and height varying from 6 m up to 35 m; under the structural point of view, these edifices consist of concrete reinforcing structures. The valley also hosts particular kinds of buildings that are part of the “Europarco Business Park” and include the two skyscrapers (named “Europarco Tower” and “EuroSky Tower”) that are 120 m and 155 m high, respectively. These towers are characterized by a rectangular plan geometry and they are composed by a steel coupled with a concrete reinforcing structure. The characteristic oscillation period of each building was calculated applying some empirical relations present in literature (NTC08, NEHRP-97, Mucciarelli et al., 2012; Kobayashi et al., 1996; Enomoto et al., 1998; Navarro et al., 1998, 2007; Guler et al., 2008, Italian Law. n.22631, USCGS 1949) with the aim of evaluating the variability of the value and choosing the values more representative (Fig. 3). 2D numerical modeling. A fully 2D numerical modeling of the geological cross section was performed through CESAR-LCPC (FEM code); an Ricker wavelet of 0 order with PGD (Peak Ground Displacement) of 1 m and an aftershock of the L’Aquila seismic crisis were applied Tab. 1 - Mechanical and dynamic properties of the materials present along the geological cross section shown in Fig. 1. Lithotechnical units Lithology Wave S velocity (m/s) Density (kg/m 3 ) 1 Human fill 118 1733 2 Sandy clay 225 1682 3 Peaty clay 150 1753 4 Clay 235 1865 5 Peat 140 1295 6 Sand 417 1957 7 Gravel 713 2141 8 Volcanic deposits 1100 1835 9 Clay 357 1865 10 Sand 417 1957 11 Gravel 1100 2141 12 Clay 1100 2141 13 Sand 1100 2141 GNGTS 2015 S essione 2.2 179