DYNAMIC ANALYSIS OF VVER TYPE NUCLEAR-POWER-PLANTS USING DIFFERENT PROCEDURES FOR CONSIDERATION OF SOIL-STRUCTURE INTERACTION EFFECTS

The dynamic response of structures due to seismic loadings is conventi onally analyzed in the time domain using substructure methods (decoupl ed system models). This procedure uses frequency-independent impedance s to represent capabilities of the soil underneath the structure. The soil parameters are tuned to the fundamental frequencies of the soil-s tructure system. This is a common procedure widely used in the prelimi nary design of power plant structures which provides conservative resu lts. However, parallel to the rapid progress being made in upgrading t he capability of data processing systems, methods and software tools h ave become available which work also in the frequency domain using com plex models (for the soil and the structure) or models in which the so il is represented by frequency-dependent impedances. This procedure (c oupled system models) also allows realistic treatment of kinematic int eraction effects and especially consideration of the embedment paramet ers of the building structure. The main goal of the study presented he re was to demonstrate the effects of different procedures for consider ation of soil-structure interaction on the dynamic response of the str uctures mentioned above. The analyses were based on appropriate mathem atical models of the coupled vibrating structures (reactor building, t urbine hall, intermediate building structures of a VVER 440/213 as wel l as the main building of the VVER 1000) and the layered soil. On the basis of this study, it can be concluded that substructure methods usi ng frequency-independent impedances (equivalent dashpots) and cut-off of modal damping usually provide conservative results. Coupled system models which allow the soil-structure interaction effects to be realis tically represented (by coupled models of the soil and the structure o r by frequency-dependent impedances) provide more accurate results. Th e advantage of the analysis using coupled system models will be demons trated and discussed, based on results obtained for the VVER 440/213 P AKS and VVER 1000 Kozloduy. (C) 1998 Elsevier Science S.A. All rights reserved.