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Thesis
Home   /   Thesis   /   Seismic analysis of the soil-structure interface: physical and numerical modelling of global tilting and local detachment

Seismic analysis of the soil-structure interface: physical and numerical modelling of global tilting and local detachment

Engineering sciences Mechanics, energetics, process engineering

Abstract

The effect of soil-structure interaction, currently not taken into account in the seismic design of civil engineering structures and their foundations in professional practice, could influence the design of load-bearing structures. Soil-structure interaction effects are linked to inertial interaction (forces in the soil-structure system) and kinematic interaction (influence of the soil-foundation contact surface) (Semblat and Pecker, 2009). A more precise analysis of these two aspects requires three-dimensional (3D) numerical modeling of the soil-foundation-structure system and its temporal response, the definition of relevant constitutive laws for materials in the nonlinear plastic regime and the characterization of their mechanical properties. This makes it possible to consider directly the reduction in soil bearing capacity resulting from loss in soil strength, and the modification over time of the seismic action at the base of the structure. In 3D soil-structure interaction models, the connection between the soil and the embedded part of the footing structure is generally considered to be rigid, and the effects of friction and up-lift are neglected.
A series of tests on the CEA's Azalée shaking table in October 1999 (CAMUS IV, Combescure and Chaudat, 2000) demonstrated the existence of complex phenomena of structural detachment from the ground during seismic shaking. This involved a 1/3 scale model of the structure resting on a sandbox, anchored to the shaking table. Tests revealed up lifting at the foundation level, leading to energy dissipation, as well as significant residual settlement and rotation. Other studies have also highlighted the significant impact of rocking and consequent up-lift at the soil-foundation interface on the seismic response of the structure (Abboud, 2017; Chatzigogos, 2007; Gajan et al., 2021; Gazetas and Apostolou, 2004), as well as the loss of elasticity and nonlinear behavior of the soil, which increases permanent settlement (Pelekis et al., 2021). However, few studies in the literature evaluate the effect of the roughness of the soil-foundation interface and propose contact laws to model settlement and up lifting during rocking of the structure under seismic action.
In the context of interaction effects, understanding the parameters influencing the behavior of the soil-foundation interface and modeling the contact surface remains a challenge. A combined experimental and numerical approach will be developed in the proposed thesis.
The main aim of this thesis is to enable the transition from the modeling of local effects (friction, up lifting) to the simulation of the structure's global response (rocking, settlement, sliding). This is achieved by identifying the experimentally measurable physical parameters that manage the phenomenon locally and, at the same time, the global dynamic parameters altered by interaction effects (change in effective height).
On the one hand, an experimental campaign will be conducted on Vesuve, a single-axis vibrating table. The experimental model will consist of a rigid box containing the reference soil and a structure placed on the surface. The behavior of the system will be monitored using pressure sensors, LVDTs, flexiforce, accelerometers, etc. In addition, a numerical modeling method will be proposed and validated by comparison with experimental results. Finally, a numerical strategy will be proposed for different study cases. The output parameters obtained by the numerical simulations will be correlated with the measured parameters in order to optimize their calibration on the one hand, and to validate the numerical approach on the other.

Laboratory

Département de Modélisation des Systèmes et Structures
Service d’Etudes Mécaniques et Thermiques
Laboratoire d’Etudes de Mécanique Sismique
IP. Paris
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