On the verification of superposition method of kinematic interaction and inertial interaction in dynamic response analysis of soil-pile-structure systems

A simplified analytical formulation has been used to verify the superposition method of two components of soil-structure interactions (SSI), namely-the kinematic interaction and the inertial interaction for estimating the dynamic response of soil-pile-structure systems (SPSS). The dynamic response analysis is conducted in the frequency domain and the soil behavior ranging from elastic-to-inelastic state is covered. The effective foundation input motion (EFIM) is obtained from shaking table model testing under 1g conditions for the kinematic interaction and the pile head impedance functions (IFs) are estimated from pile-head loading test for the inertial interaction, respectively. The EFIM and pile head IFs both have frequency and loading amplitude dependent characteristics. These experimentally recorded EFIM and pile head IFs are used as inputs in the analytical formulations to compute the dynamic response of the SPSS by superimposing the kinematic and inertial interaction. Superimposing adopts a linear interpolation method for appropriate use of the pile head IFs. The analytical (superimposed) dynamic response is then compared with experimentally measured dynamic response for verification purpose of superposition method and the comparison shows good agreement indicating that with appropriate use of EFIM and IFs, superposition method is reasonably good to produce the frequency and amplitude dependent dynamic response characteristics of SPSS. Certain discrepancies in amplification ratio and in resonant frequency particularly around the dominant vibrating modes have been observed in the comparison. The reason for such observed disagreements is possibly the difference between soil damping (hysteretic and radiation) and the difference between soil-pile stiffness.