Seismic resonance behavior of soil-pile-structure systems with scour effects: Shake-table tests and numerical analyses

The seismic resonance behavior of soil-pile-structure systems (SPSS) with scour effects is a complex problem due to the interaction of soil, pile foundation, and structure. This study performs a series of shake-table tests to identify resonance phenomena of scoured SPSS, which is represented by a simplified bridge model comprised of a lumped mass as the superstructure, a single column, and a cap supported by a 2 x 2 pile group embedded into uniform sand profiles with different scour depths. Besides, parametric analyses are conducted based on a validated numerical model to quantify the resonance periods for SPSS with different scour depths. The numerical model is characterized by a multi-dimensional soil-pile-structure coupled finite element model with a rectified soil material constitutive model to account for low effective stress effects at shallow depths. It is found that the resonance period of SPSS generally increases with increasing scour depth and excitation intensity, mainly due to the structural nonlinearity of SPSS. Quantitatively, a resonance period between 1 and 2 times the SPSS elastic fundamental period is witnessed for the examined SPSS cases. This study can be a preliminary document for the advanced seismic design of SPSS to mitigate the potential resonance behavior of SPSS with scour effects.