SOIL-STRUCTURE INTERACTION ANALYSIS USING A 1-DIRECTIONAL 3-COMPONENT WAVE PROPAGATION MODEL

Abstract eng:
The analysis of soil-structure interaction (SSI), in the case of buildings having rigid shallow foundation and negligible rocking effects, is undertaken using a one-directional three-component (1D-3C) seismic wave propagation model. Line quadratic finite elements with three nodes are used for the spatial discretization of soil columns. The three components of motion at the base of the frame structure are obtained with a reduced computation time compared with a 3D soil domain. Modeling difficulties to define the stratigraphy of a soil basin, due to the lack of geotechnical data, are avoided using a vertical soil profile. The model of a nonlinear multilayered soil profile is assembled with a multi-story multi-span frame model in a finite element scheme, solved directly. Time integration is undertaken using a Newmark implicit algorithm. An absorbing boundary condition is applied at the soil-bedrock interface to take into account the elasticity of bedrock. The frame structure with shallow foundation is modeled as rigidly connected to the soil surface, where the three components of the seismic motion are transmitted from soil to the frame base. The soil behavior is analyzed in terms of total and effective stresses. According to the Iwan-Iai constitutive model, nonlinearity of soil behavior is characterized by the shear modulus reduction curve, friction and phase transformation angles and liquefaction front parameters, obtained by numerical reproduction of dynamic triaxial tests. Differently from the free field case, when SSI is considered the soil response is different in two horizontal directions, when influenced by the interaction with a structure having different inertia in these two directions. A parametric analysis is carried out to identify dynamic features of structure, incident wave and soil profile that produce changes in the ground motion at the surface. Results are provided in terms of ground motion at the free-surface and at the building base, structural deformation, profiles with depth of maximum strains, stresses and component of motion.

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