  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 "macro-element" 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 non-linearities
is undertaken based on experience gained with earlier works. It is suggested
that the non-linearities be incorporated in the model within a unified
formalism making use of the theory of multi-mechanism 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.
