This paper proposes enhancements to the equivalent linear approach of simulating the site soil response for the seismic soil-structure interaction analysis of structures in a nuclear power plant to better represent the physical behavior of soil. The equivalent linear site response approach in frequency domain is the state of practice which is widely used to estimate site effects due to its simplicity, low computational cost, and reliability at small soil strains; however, conventional applications of the equivalent linear approach have some limitations.

This paper offers a novel framework to enhance the conventional equivalent linear soil-structure interaction analysis in frequency domain by incorporating the effects of the soil shear strength correction, structure’s weight and mass interacting with the soil, and biaxial degradation of the soil in the equivalent linear soil-structure interaction analysis.

In-Structure-Response-Spectra (ISRS) are compared with those obtained from the conventional equivalent linear and corresponding nonlinear models. A better agreement between the results from the enhanced equivalent linear and nonlinear models is observed because both approaches account for the above-mentioned physical phenomena. However, even after the proposed enhancements, the equivalent linear frequency domain approach cannot fully capture the physical behavior of the soil due to its inherent limitations to model the nonlinear and transient response of the soil-structure system.