The effects of soil-structure interaction modeling techniques on in-structure response spectra

The seismic design of nuclear power plant components is normally based on in-structure response spectra generated from an overall plant analysis which accounts for soil-structure interaction. For preliminary design, it is desirable to consider a broad range of site conditions which requires an economical analysis of the soil-structure interaction phenomenon. The purpose of this paper is to compare the results obtained from a simplified approach utilizing stiffness proportional composite damping with those obtained utilizing more refined representations of the soil-structure interaction phenomenon. Thereby, the limits of applicability of the simplified approach are determined. The structure considered for this investigation consisted of the reactor containment building (RCB) and prestressed concrete reactor vessel (PCRV) for a HTGR plant. A conventional lumped-mass dynamic model in three dimensions was used in the study. The horizontal and vertical response, which are uncoupled due to the symmetry of the structure, were determined for horizontal and vertical excitation. Five different site conditions ranging from competent rock to a soft soil site were considered. (Auth.)