Fatigue prediction of wind turbine tower considering the effect of high-tension bolt failure

• A sophisticated aeroelastic wind turbine model reveals tensile stresses on the leeward side of the tower. • The short fatigue life of high-tension bolts is accurately predicted by the full-flange FEM model. • The full-flange FEM model reveals the mechanism for the short fatigue life of the tower shell with damaged bolts. In this study, an accident at Taikoyama wind farm is investigated by the fatigue analysis of high-tension bolts and tower. Firstly, a sophisticated aeroelastic model is proposed by identifying the structural and control parameters and validated with the measured tower base bending moment. The predicted bending moment at the tower top shows that the tensile stress occurs at the downwind side of tower due to the eccentricity of the centre of gravity of rotor and nacelle. The bolt axial force is then predicted using the finite element model of the tower top with consideration of effects of ball bearings, yaw breaks and pinion gear. The predicted bolt fatigue life is about three months when the residual bolt axial force is less than 30 %, which matches the maintenance record. Finally, the stress of the tower shell is investigated by a sophisticated FEM model. It is found that the tensile stress is generated inside of the tower shell due to the leverage effect. The relationship between the local stress and the nominal stress shows the nonlinearity and the local stress in the case with damaged bolts is three times larger than that in the case with intact bolts. The predicted fatigue life of the tower favourably agrees with the observation.