Fluid-Structure-Soil Interaction Analysis Applicable to Seismic Design for Floating Seismic Isolation System

In this study, the practical seismic analysis method applicable to Floating Seismic Isolation System (Hereinafter called “FSIS”) is proposed using Fluid-Structure-Soil Interaction (FSSI) analysis approach. In the previous study of the replication analysis for the FSIS shaking test, it was revealed that the instantaneous deformation of the pool vessel due to the excitation augments the seismic response of the floating structure. When assuming nuclear power plants (NPPs) are installed onto the floating structure of FSIS in the inland, part of the pool structure of FSIS is to be embedded in the soil. In this case, the soil structure interaction (SSI) can be a significant factor affecting the floating structure by the pressure propagation from the pool walls via pool water. This study proposes modelling method of FSIS model as well as FSSI analysis methodology for FSIS paired NPPs using the commercial software, ACS SASSI. Firstly, the FSIS modelling and analyses in ACS SASSI were verified using a simplified sample model, in comparison of the analysis results obtained by another commercial software, ABAQUS. The verified modelling techniques of FSSI in ACS SASSI were then used to produce a FSSI model of the main facilities of the NPP supported on a floating structure. The sample FSIS plant model was assumed to be embedded in the soil. Through the trial FSSI analyses, the seismic isolation effect of nuclear structures with the floating structure has been confirmed for both horizontal and vertical directions even under the deformation of the pool structure with the surrounding soil during earthquakes. Future sensitivity studies will look into design parameters affecting the level of seismic isolation performance in order to optimize the design of the FSIS technology for actual use in NPPs.