Large-scale shaking table test on pile-soil-structure interaction on soft soils

The two large-scale shaking table tests of tall buildings on soft soils in pile group foundations are performed to capture the effect of the seismic pile-soil-structure interaction (PSSI) on the dynamic responses of the pile, soil, and structure. The two different model conditions are observed, including a fixed-base structure and a structure supported by 3-by-3 pile group foundation in soft soil, representing the situations excluding the soil-structure interaction (SSI) and considering the SSI, respectively. In the tests, the superstructure is a tall building with 12-story reinforced concrete frame. The pile-soil-structure system rests in a shear laminar soil container, which is designed to minimize the boundary effects during shaking table tests. The two models are subjected to various intensity seismic excitations of Shanghai bedrock waves, 1995 Kobe earthquake, and 1999 Chi-Chi earthquake events. According to the experimental and analytical results, SSI systems have longer natural periods than the fixed-base structure. In addition, soft soil has amplification effect under smaller seismic excitations and isolation effects under larger earthquake intensities. The strain amplitude at the top of pile is large, and the strain at the middle and tip is relatively small. Whereas the contact pressure is small at the top of pile and large at the middle and tip. From the dynamic responses of the superstructure, it is found that the PSSI amplifies the peak displacements and interstory drifts of the structures supported by pile group foundations by comparing with the fixed-base structure. Whereas the peak acceleration and interstory shear force of the structure are reduced considering seismic PSSI. The results show that the seismic SSI is not always favorable, however, it may increase certain dynamic responses of the structure. Consequently, the seismic SSI should be considered reasonably, providing insight towards the rational seismic design of buildings rested on soft soils.