The paper presents three engineer-oriented models based on the high-cycle accumulation (HCA) model of Niemunis et al. (2005), dedicated to the prediction of long-term deformations of offshore wind power plant (OWPP) foundations caused by wind and wave action. A sublayering model for shallow foundations under vertical cyclic loading and two different approaches (a sublayering model and a stiffness-degradation model) for monopile foundations subjected to horizontal cyclic loading are presented. The results of these models are compared to the solution from 2-D or 3-D finite element simulations with the original HCA model. Furthermore, the prediction is confronted with the prognosis of other engineer-oriented models proposed for OWPP foundations in the literature. Finally, a simplified procedure for the determination of the HCA material constants is briefly explained.
The cyclic loading of offshore wind power plant (OWPP) foundations due to wind and wave action leads to permanent deformations. They may endanger serviceability since the OWPP generators tolerate only a small tilting (0.5.–1.) of the tower. Therefore, an accurate prediction of these long-term deformations is indispensable. The high-cycle accumulation (HCA) model proposed by Niemunis et al. (2005) is a suitable tool for that purpose. It has been validated based on simulations of model tests and full-scale in situ tests (Hartwig, 2010; Zachert, 2015; Zachert et al., 2014, 2015, 2016). Up to now, the HCA model has been primarily applied in finite element (FE) simulations (e.g., Wichtmann et al., 2010b; Zachert et al., 2014, 2015, 2016). Such calculations usually demand a rather laborious 3-D model and experienced knowledge on the field of FE. To facilitate the practical application of the HCA model to OWPP foundations, several simplified engineer-oriented models for different types of foundation structures have recently been developed by the authors based on the HCA equations:
A sublayering model for the subgrade of shallow foundations under cyclic vertical loading. For example, such loading conditions are relevant for OWPPs founded on three or four separate footings. The calculation procedure using this model is similar to that in a conventional settlement calculation for foundations subjected to static loading, but with the HCA equations predicting the additional cumulative portion of settlement.