Advantages of an analysis of soil-structure interaction in a frequency domain

With the computer power available an analysis of a total soil-structure system has become possible. In this paper the advantages of an analysis performed in an frequency domain is shown: the condensation to the primary degrees of freedom, thereby conserving all the characteristic properties of the system, is straightforward; material damping based on rheological models can be considered easily; and even nonlinear problems may be investigated. The formulation is developed in a total displacement formulation, where the motion is driven by forces acting at the soil-structure interface, or more generally, at so-called interaction nodes. The total displacement formulation is compared with the classical approach, where the unknowns are the relative deformations with respect to the rigid base of the structure. These unknows are produced by inertial forces acting on the masses of the structure. In the conclusion the total displacement formulation in the frequency domain is suggested for structures with embedded elastic foundation built on a sub-grade which requires extended modeling for the mechanical representation of the structure and the sub-grade.