GNGTS 2017 - 36° Convegno Nazionale

326 GNGTS 2017 S essione 2.2 PHA = 0.245 g, corresponding to a return period of 712 years (10% probability of exceedance in 75 years) for builging of class of use III, such as the chosen one according to the Italian technical code (NTC, 2008). The adopted full-coupled numerical model. The study of the seismic response of the full- coupled system has been performed by a 2D finite element modeling by means of the ADINA code (Bathe, 1996). The width of the soil deposit has been chosen in order to minimize as much as possible boundary effect (5B where B is the width of the frame); the height of the soil deposit is 30 meters and derives from the geotechnical investigations. The model has been created according to the hypothesis of plane strain. The frame has been modeled by means of 2-nodes beam elements, by a linear elastic constitutive model characterized by the conventional properties of the reinforced concrete (E = 28500000 kN/m 2 , ν = 0.25, γ= 25 kN/m 3 ). The soil has been modeled by 2D 9- nodes solid elements, by means of a visco-elastic constitutive model, but considering its non- linear behavior, that is extremely important in soil mechanics (Abate et al. , 2007; Pecker et al ., 2010). So, soil non-linearity has been taken into account according to two different approaches. Firstly, the soil has been modeled as a linear visco-elastic material according to EC8 (EC8, 2003), which suggests degraded shear modula G and increased damping ratios D depending on the expected surface acceleration (Tab. 2). As the expected surface acceleration is greater than 0.3 g, the adopted degradation and increasing of the G and D values are shown in bold in Table 2. Tab. 2 - Values of increasing of D and degradation of V s and G 0 (from Table 4.1 EC8). expected surface Damping ratio VsVs,max GGmax acceleration [g] 0.10 0.03 0.90(±0.07) 0.80(±0.10) 0.20 0.06 0.70(±0.15) 0.50(±0.20) 0.30 0.10 0.60(±0.15) 0.36(±0.20) In a second step of the analyses, the values of G and D have been chosen according to the curves G/G 0 vs γ and D vs γ, considering the effective strain level γ obtained for each soil layer and for each different input, according to an iterative sub-routine, as it has been summarized in Tab. 3. Fig. 1 - Local geological model based on the two boreholes.