Influence of Foundation Nonlinearity on Offshore Towers Response

Abstract

The response of a fixed, offshore tower is greatly affected by the nonlinear behavior of the supporting piles. An analysis of the foundation piles response to transient dynamic loading that accounts for soil nonlinearity, discontinuity conditions at the pile-soil interface, and group effect is used to assemble the stiffness matrix of the foundation piles. A foundation stiffness matrix is added to the global structural stiffness matrix at the pertinent degrees of freedom (DOF). A model for the evaluation of wave forces on the tower members that takes into account the spatial incoherence effect on wave forces is used in the analysis. Hydrodynamic damping is evaluated, and the effect of the tower foundation behavior on it is assessed. Furthermore, the tower response to random wave forces is conducted, and the effect of foundation parameters on the tower response is examined. It was found that both the hydrodynamic damping and tower response to wave forces are greatly influenced by the foundation nonlinearity and by pile-soil-pile interaction.