GNGTS 2013 - Atti del 32° Convegno Nazionale

• a linear elastic behaviour, assuming a small strain stiffness G 0 and an initial critical damping ratio D 0 equal to G 0 ~ 3200 MPa, D 0 ~ 0.5 %, for the “Br3”; • the resonant column/torsional shear test results obtained by C.A.S.E. Project (Monaco et al. , 2012) into the fluvial-lacustrine deposits of Roio Piano for “L1”, “L2”, “L3”, “L4” and “L5” units; • a linear elastic behaviour, assuming a small strain stiffness G 0 and an initial critical damping ratio D 0 equal to G 0 ~ 9000 MPa, D 0 ~ 0.5 %, for the “Bedrock”. Tab. 1 summarized the mechanical and dynamical soil parameters of each geotechnical unit GU , by including unit weight γ, Poisson coefficient ν, shear wave velocity V S , stiffness decay curves G/G 0 and damping ratio D curves. Tab. 1 – Mechanical and dynamical soil parameters of each geotechnical unit. UG γ (kN/m 3 ) ν V S (m/s) G/G 0 and D curves Ri 17 0.2 250 MS–AQ Working Group (2010) Al 19 0.2 200 MS–AQ Working Group (2010) Dt 19 0.2 300 MS–AQ Working Group (2010) Cl 19 0.2 350 Amoroso et al. (2014) LR 19 0.2 350 Amoroso et al. (2014) Br1 20 0.2 600 Modoni and Gazzelloni (2010) Br2 20 0.2 800 Modoni and Gazzelloni (2010) Br3 21 0.2 1200 Linear elastic behavior ( G 0 ~ 9000 MPa, D 0 ~ 0.5 %) L1 19 0.2 550 Monaco et al. (2012) L2 19 0.2 600 Monaco et al. (2012) L3 19 0.2 670 Monaco et al. (2012) L4 19 0.2 740 Monaco et al. (2012) L5 19 0.2 810 Monaco et al. (2012) Bedrock 22 0.2 2000 Linear elastic behavior ( G 0 ~ 9000 MPa, D 0 ~ 0.5 %) 1D and 2D Numerical modeling. Numerical analyses of seismic site response were carried out using the computer codes EERA (Bardet et al. , 2000), a monodimensional linear equivalent model, and QUAD4M (Hudson et al. , 1994), a bi-dimensional linear equivalent model. In particular, EERA iterates the analysis in order to follow the variation of normalized shear modulus G/G 0 and damping ratio D with shear strain. It assumes simplified soil deposit conditions such as horizontal soil layers of infinite extent. Instead, QUAD4M is a dynamic, time domain and equivalent linear two-dimensional computer program. It uses a finite elements procedure approximating the domain with a mesh of finite number of triangular and/or quadrilateral elements interconnected at their common nodes. The code solves the approximated system by using a step-by step integration in the time domain: the parameters are fixed for the whole duration of the input signal and the computation is repeated with the update of the stiffness and the damping matrices, as happens in the one- dimension code SHAKE (Schnabel et al. , 1972; Idriss and Sun, 1992). QUAD4M propagates P and/or SV waves with vertical incidence. The artificial reflection of seismic wave should be minimized at the domain boundaries, as well as at the underlying half-space,to represent the response of an infinite field condition. Lysmer and Kuhlemeyer (1969) introduced base 175 GNGTS 2013 S essione 2.2