Welded Connections of Wind Turbine Towers under Fatigue Loading: Finite Element Analysis and Comparative Study

Increased contemporary energy needs have led to multiple investments on wind power plants and structural improvements are considered necessary for the construction of taller, more robust and more economical structures. Tubular steel wind turbine towers that are the prevailing structural configuration, demand welding of circular subparts to construct the tower structure. These circumferential welds between tower subparts and between the tower and the connecting flanges are proved to be prone to fatigue failure, since cracks are observed in these areas of already constructed wind towers. The aim of the present work is to enlighten weld design procedures of wind turbine tower welds using damage accumulation methods. For the purposes of the comparative study, two towers of same height differing in shell thickness distribution are taken into account. The towers are compared numerically and analytically following two methods of calculating fatigue loads for structures; the first is an analytical method proposed in design codes and the second is by using artificial loading histories produced by the National Renewable Energy Laboratory software. In both methods, shell thickness is proved to be a decisive factor for the fatigue life of the structure and it is often a challenge to design an economic structure with sufficient fatigue life. From the comparison of the tower’s welds fatigue life, useful outcomes have been found on the precision of the methods compared and the relation of fatigue life and material used for construction.