A MACRO-ELEMENT FOR DYNAMIC SOIL-STRUCTURE INTERACTION ANALYSES OF SHALLOW FOUNDATIONS

The scope of the paper is to present some aspects of the development of a “macro-element” for dynamic soil-structure interaction analyses of shallow foundations. Initially the concept of “macroelement” is introduced and is illustrated with the aid of a very simple example originating from structural engineering. Then the link is made with the modeling of the dynamic response of shallow foundations and the objectives and structure of such a tool are described with reference to the specific configuration of a circular footing resting on the surface of a heterogeneous purely cohesive soil. The principal features of the “macro-element” are then presented; the soil-structure interaction domain is reduced to a point that coincides with the center of the footing and all the (material and geometric) non-linearities are lumped at this point. A discussion on the most appropriate way to treat these nonlinearities is undertaken based on experience gained with earlier works. It is suggested that the nonlinearities be incorporated in the model within a unified formalism making use of the theory of multimechanism plasticity. Initial results concerning the definition of the ultimate surface for such a plasticity model, corresponding to the seismic bearing capacity of the foundation, are finally presented.