In this study, the cyclic responses of an offshore wind turbine with a tripod foundation installed on an actual site were evaluated in a centrifuge. To understand the behavior of the turbine at the site, the site soil conditions, environmental loads, and real offshore wind turbine structure installed at the actual site were modeled by considering the centrifuge scaling law. From a series of cyclic loading tests, the cyclic responses of the tripod foundation were evaluated in terms of temporary/permanent displacements and cyclic stiffness. Moreover, the long-term behavior of the tripod foundation was predicted from the experimental results. The test results showed that the initial stiffness of the soil–foundation system decreased as the loading amplitude increased and that the stiffness increased with the number of cycles due to soil densification. The findings revealed that the cyclic behaviors of the tripod were more affected by the load amplitude than the number of cycles. In addition, the permanent rotation increased logarithmically with the number of cycles. A simple method to predict the displacement and change in the foundation stiffness of the actual wind turbine is proposed based on the results of the model tests. The results of this study also provide key insights into the long-term cyclic behavior of tripod foundations for offshore wind turbines.
Seismic evaluation of offshore wind turbine by geotechnical centrifuge test
