GNGTS 2021 - Atti del 39° Convegno Nazionale

GNGTS 2021 S essione 2.2 298 A total of 192 2D models of symmetric two-layered basins were analyzed, with soil 1 overlying soil 2. An elastic seismic bedrock was assumed, whose geometry can be fully described by the Bard and Bouchon (1980) semi-sine-shaped formulation: 2 given control point located at a distance x from the center of the basin surface as obtained analysis, and S a, 1 D ( T , x ) is the response spectrum at the same control point from 1D analys A total of 192 2D models of symmetric two-layered basins were analyzed, with soil 1 over 2. An elastic seismic bedrock was assumed, whose geometry can be fully described by the Bouchon (1980) semi-sine-shaped formulation: h ( x ) = H for | x | < L i h ( x )= H 2 [ 1 + cos π ( x − Li ) Lo ] for L i < | x | ≤ L o + L i h ( x ) = 0 for | x | > L o + L i (2a) ) ntrol po H r ( ) x L 0 where S a, 2 D ( T , x ) is the elastic pseudo-acceleration response spectrum at 5% damping given control point located at a distance x from the center of the basin surface as obtained analysis, and S a, 1 D ( T , x ) is the response spectrum at the same control point from 1D analys A total of 192 D ls of sy metric two-layered basins wer analyzed, with soil 1 over 2. An elastic sei mic bedrock sumed, whos geometry can be fully d scribed by the Bouchon (1980) semi-sine-shaped formulation: h ( x ) = H for | x | < L i h ( x )= H 2 [ 1 + cos π ( x − Li ) Lo ] for L i < | x | ≤ L o + L i h ( x ) = 0 for | x | > L o + L i (2b) a, 2 D i tr l i t l t t i t fr t t r f t i rf t i a l i , a, 1 D ( , ) i t r tr t t tr l i t fr l t t l f l f tri t -l r i r l , it il r 2. An elastic s i i r , geometry can be fully described t Bouc ( ) i- i - f r ulation: ( ) = for i ( ) [ 1 cos π ( x − Li ) ] for i o + i ( ) f r o + i (2c) where H is the maximum depth of the soil deposit at the center of the basin; 2 L i is the inner width, i.e., the extension where depth is H ; L 0 is the outer width, i.e., the extension of basin edges; L =2( L i + L 0 ) is the total width of the basin. The general model geometry is shown in Fig. 1, where only the semi-width of the analyzed model is represented. Pseudo-acceleration elastic response spectra for use in Eq. (1) were obtained by means of numerical response analyses performed using the LSR-2D (Local Seismic Response 2D) finite element software (STACEC 2017). The material properties assigned to each layer and underlying bedrock are given in Table 1. Layer V S [m/sec] � [kg/m 3 ] G 0 [MPa] D 0 [%] υ Soil 1 (top layer) 200; 300 1800 72; 162 1.4 0.30; 0.35 Soil 2 (bottom layer) 450; 600 2000 405; 720 1.4 0.30; 0.35 Bedrock 800; 1100 2300 1472; 2783 0.05 0.15 Fig. 1 – Half-width cross section scheme of the analysis models Tab. 1 - Mechanical properties of basin materials ( V S : shear wave velocity, � : density, G 0 : shear modulus, D 0 : damping ratio, υ : Poisson coefficient). els of symmetric two-layered basins were analyzed, with soil 1 overlying soil edrock was assume , whose geometry can be fully described by the Bard and -sine-shaped formulation: for | x | < L i (2a) − Li ) Lo ] for L i < | x | ≤ L o + L i (2b) for | x | > L o + (2c)