Soil and pile interaction could significantly contribute to the response of the system and should be considered in the design prospect. To address some of the uncertainties, a series of 1 g shaking table tests followed by numerical simulations were conducted to address the seismic response of free-head single piles embedded in dry sand subjected to seismic waves of which horizontal acceleration and bending moments are the prime indexes. Subsequently, the validated numerical model was employed to perform parametric studies, focusing on normalized induced kinematic forces based on the soil profile type. The numerical results showed that not only does the soil profile type considerably affect the amplitudes of the maximum normalized seismic forces but also the distributions of these response parameters are highly dependent on soil type. The results also demonstrated that neglecting slippage and/or separation along the soil-pile interface leads to underestimation of the maximum normalized kinematic bending moment and shear force by up to 17.5% and 70%, respectively. Soil type also affects the induced forces by about 60% indicating that the design consequence of which could be dire. Therefore, it is concluded that the effects of slippage and/or separation can be considerable and hence, should be taken into consideration to prevent probable damages in seismic areas.

In recent years, strong earthquakes have caused a lot of damage around the world. In order to prevent such damage, proper evaluation of the seismic performance of buildings is absolutely necessary. However, the current analysis procedure in seismic design assumes fixed boundary conditions for the foundation and neglects the influence of the substructure on the superstructure. Previous studies have shown that the type of foundation affects structural responses during earthquakes. However, most of these studies have focused on single-degree-of-freedom (SDOF) structures and have not considered variations in response according to different substructure types. This study aims to investigate the effects of different substructures on ground motion and corresponding responses of the superstructure. Centrifugal simulations were conducted on a multi-degree-of-freedom (MDOF) superstructure, including a Half-embedded with Pile foundation, a fixed deep basement, and a Shallow foundation. The experimental results indicate that in the case of a half-substructure with a pile foundation, there was no significant difference between free field motion and foundation motion due to the pile foundation. However, in the case of a fixed deep basement, the embedment effect was most pronounced, especially in the short period range of 0.1 s to 0.5 s in the response spectrum. This resulted in a notable reduction in the spectrum. The analysis of the response spectra of foundation motion and free field motion revealed that the reduction effect was absent in the half-embedded with a pile foundation, but it was prominent in the fixed deep basement. Notably, the ratio of response spectrum increased in the fundamental period of the substructure. In the case of a shallow foundation, it was observed that foundation motion experienced larger amplification compared to free field motion. Shallow foundations have a relatively low stiffness of the substructure and are influenced by the inertial forces of the superstructure. Additionally, this tendency is believed to be more prominent due to the imperfectly fixed boundary conditions of shallow foundations to the ground. However, apart from the increase in foundation motion, the response of the superstructure was not proportional to it. These results contribute to a better understanding of the changes in seismic load and the response of multi-degree-of-freedom superstructures according to the type of substructure. The seismic design of the superstructure is safer and more reasonable when considering the effects of the type of substructure.