Optimization of supporting structures for offshore wind energy plants

Procedures for optimization and maintenance of welded joints frequently used in offshore structures are studied within an ongoing research project at KIT and BAM. Key issues of the research work are the fatigue performance of girth welds as well as the effectiveness of a post weld treatment subsequent to weld repair. This paper covers the classification of girth welds according to different standards and recommendations. Based on this overview the necessity of own experimental investigations is substantiated and experimental test results of full-scale fatigue tests at KIT and BAM are presented. The fatigue strength of girth welds is evaluated in terms of S-N curves and significant parameters affecting the fatigue behavior are discussed. Considering efficient maintenance procedures, the effectiveness of a post weld treatment following weld repair measures is investigated. For this purpose high frequency mechanical impact treatment (HFMI) is used to enhance the fatigue life of rehabilitated joints. Fatigue tests are conducted in order to quantify the benefit of a post weld treatment and recommendations are given for fatigue design.