Offshore wind turbines are subjected to tight tolerances concerning their natural frequencies and permanent rotation at the end of their lifetime. Therefore, design methods should accurately account for the effect of cyclic loading on monopiles. The most commonly used procedure for calculation of the behaviour of laterally loaded piles is the P-y curve method. Accounting for cyclic loading within the P-y curve framework is trivial in most cases and needs improvements. A simple procedure is presented herein for the extension of the P-y curve framework for modelling cyclic response. Unloading paths with or without gapping are introduced to account for irreversible displacements. Similarly to creep tests, cyclic loading exhibits three main types of response: stabilisation of accumulated displacements, ratcheting, and unstable increase of accumulated displacements up to failure. Therefore, we explore the use of existing creep models for modelling cyclic response. We focus here on stabilised cyclic response and implement Kelvin-Voigt rheological models in series with P-y curves. This procedure is validated by comparing the numerical results with data recorded in field pile tests performed in soft rock.
A. Lovera, S. Ghabezloo, J. Sulem, M. F. Randolph and E. Palix
Keywords: cyclic loading, P-y curves, monopiles
Publisher: DFI