Impacts of mat and pile foundations on floor response spectra of SMR structures considering soil–structure interaction

Small Modular Reactors (SMRs) offer advantages over traditional large-scale nuclear power plants, including scalability and cost-effectiveness. While mat foundations are commonly used for SMR structures, they have limitations in some seismic scenarios. Pile foundations present a promising alternative, yet their impact on the floor response spectrum (FRS) of SMR structures remains largely unexplored. This study examines the FRS characteristics of SMR structures with pile and mat foundations, accounting for soil–structure interaction (SSI). Analyses are conducted for three types of soil sites (hard, stiff, and soft) and two embedment depths (10 m and 25 m). Results show that at a 10 m depth, foundation type significantly influences spectral shape and amplitude of FRS, especially on soft soil sites. At a 25 m depth, however, the foundation type has minimal impact. These findings provide essential insights for seismic design and foundation selection in SMR structures across diverse site conditions. As the SSI analyses employed equivalent-linear soil behavior and tied mat–soil interfaces, the obtained FRS variations represent an upper-bound stiffening response, particularly for the 10 m embedment cases.