Fatigue evaluation of grouted connections subjected to Markov matrix based random loading

Abstract

Grouted connections in offshore wind turbines often experience random cyclic loadings due to harsh marine environment and are prone to fatigue damage. It is significant to evaluate their fatigue life for the durability of the offshore wind turbine. In this study, a fatigue evaluation exercise of grouted connection of wind turbine structure with finite element method is completed based on standards of Det Norske Veritas, i.e., DNVGL-ST-0126 and DNVGL-RP-C203. Loadings of variable amplitude summarized in the format of Markov matrix are firstly separately applied to the grouted connection models, and refined finite element models were analyzed to obtain stress states of the materials at critical locations. Hot spot stresses of welded shear keys and nominal stresses of grout were calculated and their damage indices were then accumulated for predominant loading directions. Furthermore, an integrated program has been designed to make the process of fatigue assessment convenient and efficient. Finally, fatigue evaluation is conducted for the grouted connection based on the proposed method. The process was applied to the grouted connection of an actual wind turbine and the results indicated that the damage indices are less than 1/3. The proposed method can serve as a useful tool for the actual engineering design of grouted connections.