According to the large-scale shaking table tests

the seismic responses of the base isolated multi-story structure and the isolation effectiveness of isolation layer are compared and studied for the structure built on the different soil foundations

such as the rigid foundation

the hard soil foundation and the soft soil foundation.The result shows that the SSI effects on the dynamic characteristics of the base isolated structure are obvious by the type of soil foundation.With the soil foundation softening

the first-order natural frequency of the isolated structure decreases and the damping ratio increases obviously.The effect of the SSI on the seismic responses of the isolated structure are also changed by the stiffness of soil foundation.The SSI effects may increase or decrease the seismic response of the isolated structure built on the soft soil foundation However

the SSI effects on the hard soil foundation have the same influence on the dynamic responses of the isolated structure with the rigid foundations.At the same time

the isolation efficiency of isolation layer is also affected by the stiffness of foundation and the dynamic characteristics of the input ground motions.Especially

the stiffness of foundation has the maximal impact

and the isolation efficiency of isolation layer decreases with the decreasing of the stiffness of foundation.