Identifiable Stress State of Wind Turbine Tower-foundation System Based on Field Measurement and FE Analysis

This research focuses on the vibration response of the wind turbine tower–foundation system to identify and describe the stress state of the system. First, the movements of an existing wind turbine tower-foundation system were measured using accelerometers at the top and middle of a 20 m tower. Elastic behaviors of the tower and anchor bolts that transfer motion to its foundation were verified using various strain gauges. The spectrum of the strain of the anchor bolts generally agreed with the acceleration spectrum. Next, three-dimensional nonlinear FE analyses were performed to identify stress states of various parts of the system. The FE model was verified through data obtained from a field-based free vibration test. Then, the model was examined with a displacing obtained by processing the field measurement data. The obtained accelerations of the tower were consistent with the measured data; however, the calculated strain of the anchor bolts was larger than the measured strain. Further analysis was conducted to predict the ultimate state at failure. The deformation and stress of the anchor bolts suggested that the anchor bolts are the dominant load-carrying mechanism and failure mode of the tower-foundation system.