Shaking table test on high-rise isolated structure on soft soil foundation

In order to investigate the seismic behavior and isolation effectiveness of a high-rise isolated structure on soft soil foundation, the shaking table tests of a high-rise isolated model on rigid and soft soil foundation were conducted. A laminar shear soil container was fabricated to minimize the boundary effects. With the similitude of the soil pressure, five-story steel frame models of aspect ratio 4, either with or without rubber bearings, supported by a pile group, and seated on a silty clay deposit, were subjected to different strong ground motions. From the results, it is found that soil-structure interaction (SSI) effects on high-rise isolated structure models are not as important as those in unisolated counterpart. Due to SSI, the natural frequency of the isolated model system is obviously reduced, and damping ratio largely increased. The efficiency of the presented isolation system on soft soil is confirmed. However, the ratio of peak acceleration of the isolated model to the unisolated one on soft soil is increased, with the isolation effectiveness reduced relatively. SSI can increase or decrease the seismic response of high-rise isolated model, depending on not only the type but also the intensity of the earthquake motion. It is also observed that the acceleration response spectrum of the foundation input motion agrees well with that of the free-field motion for the isolated structure. While, for the unisolated one, it is close to those of the ground motions at greater depths of soil.