Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
Results
Abstract This paper demonstrates the effects of soil structure interaction due to cyclic loading on foundations for offshore wind turbines. It is shown how the bending moment of model test piles is influenced by horizontal cyclic loading. Furthermore the development of contact pressures below a cyclically loaded shallow foundation for offshore wind turbines is analyzed. A considerable redistribution of the contact pressures was observed and can be explained by the inhomogeneous accumulation of strains due to the cyclic loading. Both effects in different scales (model tests and in situ test) were successfully predicted by numerical simulations using a high cycle accumulation model. Introduction The prediction of accumulated deformations of foundations for offshore wind turbines is still a challenging task. Until now there has been a lack of validated soil models for the accurate description of the soil behaviour, when subjected to cyclic loading. The high cycle accumulation (HCA) model proposed by Niemunis et al. (2005) is based on hundreds of cyclic triaxial tests on different sands and has been continuously improved during the last decade. Latest topics are discussed by Wichtmann & Triantafyllidis (2016) as well as Niemunis and Wichtmann (2014). Beside the application on laboratory tests, the HCA model has been validated by comparison of numerical simulations with various cyclic model tests (Wichtmann, 2005, Solf, 2012, Zachert, 2015) and with an in situ test on a cyclically loaded shallow foundation (denoted as test foundation in the following), see Zachert et al. (2014, 2015) and Zachert (2015). Cyclic loading generates accumulated deformations in the soil. In combination with the foundation structure, these deformations lead to e. g. stress redistributions which might affect the behaviour of the whole structure significantly. Such soil structure interaction (SSI) under cyclic loading will be discussed in this paper. As examples model tests on monopiles and the full scale test performed on the shallow test foundation will be used. The effects of cyclic loading on the structures were measured during the model tests and the in situ test. Both were simulated by finite elements incorporating the HCA model for the cyclic loading.
Abstract The influence of several parameters on the accumulation of residual deformations in sand subjected to a high-cyclic loading has been studied in drained triaxial tests on fine sand. The influence of grain shape has been found dependent on the amplitude and pressure level. The larger the contents of fines and shell fragments, the larger are the cumulative deformations. Based on a test series with frequently changing amplitudes it is demonstrated that a bundling of the cycles to packages with constant amplitude is justified. Such bundling is indispensable for the application of a high-cycle accumulation (HCA) model. In another series the influence of multiple changes of the polarization of the cycles has been found less important than previously thought. An effect not captured in the HCA model yet has been detected in a series of multistage tests: A change of the average stress between bundles of cycles partly or completely erases the memory of the sand regarding its cyclic preloading history. A strong influence of the sample preparation technique on the long-term deformations measured in drained cyclic triaxial tests is also demonstrated. In contrast, the cyclic response is rather independent of the angle α between the polarization of the cycles and the bedding plane orientation. INTRODUCTION The cyclic loading of offshore wind power plant (OWPP) foundations due to wind and wave action leads to permanent deformations which may endanger the serviceability of the structure. An accurate prediction of these long-term deformations is indispensable. The high-cycle accumulation (HCA) model proposed by Niemunis et al. (2005) can be applied for that purpose, either in finite element (FE) simulations (Zachert et al., 2016) or by using simplified engineer-oriented models based on the HCA equations (Triantafyllidis et al., 2016). The HCA model has been developed based on an extensive laboratory program with drained cyclic tests on sand (Wichtmann, 2005) and considers the most important influencing parameters, i.e. the strain amplitude caused in the soil by the cyclic stresses, soil density, average stress and cyclic preloading history.
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Platform design (0.70)
- Health, Safety, Environment & Sustainability > Sustainability/Social Responsibility > Sustainable development (0.61)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Installation equipment and techniques (0.61)
Prediction of Long-Term Deformations of Offshore Wind Power Plant Foundations Using Engineer-Oriented Models Based on HCA
Triantafyllidis, Theodoros (Karlsruhe Institute of Technology) | Wichtmann, Torsten (Karlsruhe Institute of Technology) | Chrisopoulos, Stylianos (Karlsruhe Institute of Technology) | Zachert, Hauke (Karlsruhe Institute of Technology)
Abstract The paper presents several engineer-oriented models based on the 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 sub-layering model for shallow foundations under vertical cyclic loading and two different approaches (sub-layering model and stiffness degradation model) for monopile foundations subjected to a horizontal cyclic loading are presented. The results of these models are compared to the solution from complete 2D or 3D finite element simulations with the 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. INTRODUCTION The cyclic loading of offshore wind power plant (OWPP) foundations due to wind and wave action leads to permanent deformations which may endanger the serviceability of the structure. An accurate prediction of these long-term deformations is indispensable. The high-cycle accumulation (HCA) model proposed by Niemunis et al. (2005) is suitable 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., 2016). Up to now, the HCA model has been primarily applied in finite element (FE) simulations (e.g. Wichtmann et al. (2010); Zachert et al. (2016)). Such calculations usually demand a rather laborious 3D model and experienced knowledge on the field of FE. In order to facilitate the practical application of the HCA model to OWPP foundations, recently several simplified engineer-oriented models for certain types of foundation structures have been developed by the authors based on the HCA equations:
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Platform design (1.00)
- Health, Safety, Environment & Sustainability > Sustainability/Social Responsibility > Sustainable development (0.81)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Installation equipment and techniques (0.81)