IMPEDANCE MATRICES AND INTERPOLATION TECHNIQUES FOR 3-D INTERACTION ANALYSIS BY THE FLEXIBLE VOLUME METHOD

Most currently available procedures for the dynamic analysis of three dimensional soil-structure systems have some restrictions regarding the type of system that can be analysed. Hence, a new technique, the flexible volume method, has been developed. This method can handle much more complex problems than current methods of analysis. It can handle flexible foundations of arbitrary shapes embedded in a layered viscoelastic halfspace, structure to structure interaction, and pile foundations. The only limitation being cost and available computer storage space.;The method proposed differs from other substructuring techniques in the manner in which the soil and the structure are partitioned. By assuming that the interaction occurs at all the nodes connecting the structure to the foundation, the general three dimensional impedance problem is reduced to a series of axisymmetric solutions of the response of a layered site to point loads. A perfect halfspace can be modeled by the addition of special energy absorbing boundaries at the base of the model.;The method works in the frequency domain using the complex response method. Transient problems can be handled by Fast Fourier Transform techniques. In order to make the method cost-effective, a new interpolation scheme is proposed. This scheme significantly reduces the number of frequencies where the response of the system (complex transfer functions) need to be computed.;The method has been implemented in a system of computer programs called SASSI. Several solutions obtained by this program show good agreement with known analytical solutions. This favorable comparison provides verification for both the method and the SASSI computer code.;SASSI was also used to study the structural response of the Humboldt Bay Nuclear Power Plant during the Ferndale Earthquake of June 7, 1975. The response obtained from SASSI was compared with actual recordings made at the plant and with the response obtained from a plane strain analysis using FLUSH. From this investigation it was shown that for heavy, stiff embedded structures, soil-structure interaction effects are very important. Furthermore, the response in the foundation obtained from a FLUSH analysis can be accurate enough for engineering purposes.