Improving the accuracy of soil-structure interaction analysis through the generalized subtraction method

Abstract

This study proposes the Generalized Subtraction Method (GSM) to improve the accuracy of Soil-Structure Interaction (SSI) analysis, which is crucial for seismic design of large structures such as nuclear power plants. Although the existing Subtraction Method (SM) used in the SASSI program is advantageous in terms of computational efficiency, the method has limitations that can cause abnormal responses in high-frequency regions. To address this issue, this study introduces a method of defining additional interaction nodes in the excavated soil to shift the spurious fundamental natural frequency of the excavated soil with fixed boundary conditions at the interaction nodes to above the maximum frequency of interest. By adjusting the fundamental natural frequency through iterative eigenvalue analysis, the proposed method provides stable and accurate SSI analysis results even in high-frequency regions. Numerical analysis results for two example models showed that the GSM achieved a similar level of accuracy to the Direct Method (DM) while using fewer interaction nodes than the existing Modified Subtraction Method (MSM).