Centrifuge modeling on seismic response for soil-foundation-building systems supported by shallow foundations and deep basements

This paper evaluates the soil-foundation-structure interaction (SFSI) of structures supported by shallow foundations and deep basements using a dynamic centrifuge test at 60 g in dry sand. Two testing series were investigated including shallow foundation and deep basement systems. Each series comprises one free-field ground motion case and two model structure cases using single-degree-of-freedom (SDoF) and two-degree-of-freedom (2-DoF) on various types of foundations. To address the effects of the SFSI, the spectral accelerations imposed on the model structures supported by respective foundation systems were measured using different ground input motions. All dynamic tests were performed on one directional shaking table mounted with an equivalent shear beam containing dry dense sand with a relative density of 77 to 80%. The average shear-wave velocity, measured by the bender element tests, ranges from 193 to 228 m/s, corresponding to a site natural period of 0.74 to 0.61 s, at which the site amplification of the soil models was observed under free-field conditions. The fundamental period of the structure installed on the shallow foundations was lengthened due to the SFSI effect. The soil-foundation-structure interaction with the shallow foundation was maximized for the short structure period of SDoF as the spectral acceleration was reduced owing to the rocking motion of the foundation. Contrastingly, as a long period structure of 2-DoF on the shallow foundation, the rocking effects were minimal due to the significant spectral acceleration response of the system, causing reduced influence of SFSI particularly in low-intensity earthquakes. The fixed base response of SDoF structure on deep basements was 1.48 times higher than those placed on shallow foundations in the Northridge-SM case owing to induced vibrations of the soil-basement system. The seismic behavior of the structures on the basement was reduced compared to structures on shallow foundations. The interaction between the foundation types and the surrounding soil can significantly influence the seismic response of the structure. In particular, the period of the 2-DoF on the underground structure was shorter. It was caused by both differences in the degrees of freedom of the soil-foundation system (depending on foundation type) and stiffness contrasts between shallow foundations and basement.