Shaking Table Experiments and Simplified Numerical Simulation of a Shallow Foundation Test Model

Abstract eng:
The set of experiments carried out at the Public Works Research Institute, Tsukuba, Japan, is a unique opportunity to analyze the seismic behaviour of shallow foundations under seismic loading of various levels of intensity up to complete failure. The experimental set up consists of a shallow foundation test model (0.5m x 0.5m in plan) located at the surface of a laminar shear box (4m x 4m in plan and 2.1 m high), filled in with dry Toyoura sand. The box is shaked at its base with a sequence of excitations of various degree of intensity, representative of the seismic input motion used for seismic design in Japan. In this contribution the experiments are simulated using a simplified approach consisting of a single degree-of-freedom structure founded on a compliant foundation with 3 degrees-of-freedom (vertical, horizontal, rocking). The nonlinear behaviour of the soil-foundation system is allowed by numerical modelling using a nonlinear elasto-perfectly plastic macro-element, defined by a suitable yield surface and plastic flow rule. The results of the numerical analyses are very satisfactory in terms of the accurate simulations of the time history of overturning moments, driving the nonlinear behaviour of the foundation. The simulation of the accumulated settlements and rotations was much more difficult: satisfactory results were obtained by using a suitable stiffness degradation rule as a function of the total plastic rotation accumulated during shaking. These results throw light on the debated issue of the foundation ductile behaviour during strong seismic shaking and on its possible role in the evolution of performance-based design concepts including nonlinear soil-structure interaction.

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