###### Abstract  
After coupling long-period seismic motions with the soil-structure interaction (SSI) effect, isolated structures can easily be resonated, and the seismic response of the structure is significantly enhanced. The SSI effect can alter the dynamic characteristics of a structure, resulting in a deviation between the assumed seismic-isolation effect of the rigid foundation and the theoretical results. To investigate the dynamic characteristics and seismic-response laws of interlayer structures considering SSI under long-term seismic motion, four types of ground motions (near-field ordinary, far-field ordinary, near-field pulse, and far-field harmonic ground motions) were selected, and two structural models (rigid-foundation and soft soil foundation interlayer seismic-isolation structure models) were established. Experiments were conducted using a combination of shaking-table tests and finite-element simulations. The results show that the use of the SSI effect caused the decrease in the acceleration response of the upper structure of both models under four types of seismic motions and increased the seismic peak ground acceleration (PGA). In addition, the weakening of the acceleration response of the upper structure under ordinary seismic motion is significant for longer periods of seismic motion. Furthermore, when considering the SSI effect, the displacement response ratio under long periods and ordinary ground motions is greater than that of rigid foundations, and the horizontal deformation of the isolation layer under long-period ground motions is greater than that under ordinary ground motions. This shows that the SSI effect weakens the interlayer shear force under ordinary seismic action more than that under long-period seismic action. When PGA increases, the interlayer shear force response of the interlayer isolation structure model with a soft soil foundation under a long-period seismic action may be smaller than that of the rigid-foundation model. long-period ground motion; story isolation; SSI effect; shaking-table test; seismic response +
Footnote †: journal: Applied Sciences  
change the characteristics of ground motion, increase structural damping, and enhance the structure itself over an extended period; this in turn may affect the dynamic reaction of the seismic-isolation structure, causing a large deviation between the actual seismic responses of the isolated structures created using soft- and rigid-foundation soils [6; 7; 8]. [PERSON] et al. [9] analyzed the dynamic response of the isolation structure by considering the SSI by simulating the foundation with springs and dampers, and they pointed out that the SSI effect obviously increased the displacement and shear force of the bottom layer of the isolation structure. By establishing the lumped parameter SR model, [PERSON] et al. [10] derived a mathematical formula suitable for analyzing soil-isolation structure interaction and verified its applicability through numerical examples, pointing out that the SSI effect showed a greater impact on high-rise isolation structures than on mid-low isolation structures. Based on [PERSON]'s research results, [PERSON] et al. [11] improved the simplified analysis method of interlayer shear force and interlayer deformation of a soil-isolated structure. The results of their theoretical analysis showed that the influence of the rotation effect of the isolation layer on the interlayer shear of the isolation structure should be considered only in the case of large earthquakes. [PERSON] et al. [12] used the isolation structure model of the soil-friction pendulum system to study the structural dynamic response, and the results showed that SSI effect enhanced the seismic response of isolated structures. [PERSON] and [PERSON] et al. [13; 14] used the ABAQUS software (version 2021) to build a three-dimensional finite-element model to numerically analyze the seismic response of soil-isolation structures with isolation supports.