New method to calculate the kinematic response of offshore pipe piles under seismic S-waves

Abstract

Earthquake-induced horizontal vibration is a major concern for offshore engineering. This paper developed an analytical framework aiming at determining some kinematical response factors towards open-end offshore pipe piles under seismic S-waves. The vibrating of pile in horizontal direction is characterized by the Timoshenko beam theory. The dynamic soil impedance and hydrodynamic force are respectively calculated based on the porous medium assumption and radiation wave theory. The proposed solutions can determine the kinematic response factors of piles and have been verified via comparing against the existing findings. The effects of water depth, exterior and interior hydrodynamic pressure, the depth of embedment as well as axial loads on the kinematic response and deformation performance of offshore pipe piles are discussed in a parametric study. To summarize, the main findings of this study are as follows: (1). Without considering hydrodynamic pressure, the vibration frequency with largest kinematic response will be overestimated, while the deformation and curvature ratio would be underestimated; (2). For offshore pipe piles, both inner and outer hydrodynamic pressures have significant impacts, and their influence is in the same degree.