Dynamic Response Characteristics of Hollow Steel Single Pile Under Vertical Excitations

In this present study, the nonlinear behavior of a single hollow steel pile having an outer diameter of 0.114 m and length of 3 m was investigated under vertical excitations of rotating machine. Forced vibration tests were performed in the field to determine the dynamic responses of the single pile for four different eccentric moments. First time-acceleration responses of the single pile were measured for different frequencies and finally from that the frequency-amplitude response curves have been obtained for different excitation forces. It is observed from the field test results that the measured frequency-amplitude response curves exhibit nonlinear behavior of the soil-pile system by showing the decrement in resonant frequencies and disproportional increment in resonant amplitudes with the increase of excitation intensities. Additionally, the inverse analytical method of Novak is used to quantify the variation of stiffness, damping, and effective mass of the pile for different excitation intensities using the measured response curves. It is observed that the calculated damping values are increased with the increase of excitation forces. However, the effective mass and average stiffness values are decreased with the increase of excitation forces. The frequency-amplitude response curves are also back-calculated using the theory of vertical vibration with the calculated parameters of the soil-pile system. The back-calculated response curves are compared with the field dynamic test results and it can be seen from the comparison curves that the dynamic nonlinear response obtained from the theoretical analysis have a very close match with the field test response curves.