Zur Verformungsprognose von Monopile-Gründungen infolge zyklischer Belastung mit veränderlicher Amplitude

On the deformation prediction of monopile foundations due to cyclic loading of varying amplitude

The foundations of the offshore wind turbines should be designed according to the latest scientific knowledge. Monopiles showing 6-7 m in diameter represent one kind of such foundation structure. The main loading acting on those foundations is horizontal resulting from the wind and wave action. Meanwhile sufficient numbers of model tests have been carried out, theoretical models are available describing the physical phenomena governing the monopole behavior under high cycle loading are available as well. In parallel the existing recommendations [1, 2] describe methods for the design and prediction of the performance of those foundation structures. The paper attempts in a critical review of the in [1] proposed formulas and methods to describe their drawback especially in the case of more than two cyclic amplitudes. It is shown that the deformation superposition has to be revised in order to fulfill the superposition principles as given by Stewart [3]. Using a simple example as already published in [4] it is shown that the strain hardening method used in the literature is unsuitable to solve the problem under consideration. In the paper particular attention is paid to the prediction models for the monopile structure under cyclic loading with varying amplitude.