Issue 9

C. M. Sonsino, Frattura ed Integrità Strutturale, 9 (2009) 3-12 ; DOI: 10.3221/IGF-ESIS.09.01 3 Structural durability assessment of welded offshore K-nodes by different local design concepts C.M. Sonsino Fraunhofer Institute for Structural Durability and System Reliability LBF, Darmstadt, Germany; c.m.sonsino@lbf.fraunhofer.de A BSTRACT . The structural durability design of complex welded structures should not rely only on one single design method but should apply different methods for assuring the reliability of the assessment. In this context the application of the structural stress concept, notch stress concept and crack propagation concept are discussed through the example of K-nodes used in energetic offshore constructions like oil platforms or wind power plants, presenting the state of the art. K EYWORDS . Welded joints; Steel; Design concept. I NTRODUCTION he most important parameters controlling the durability of welded structures are the service loadings, mechanical as well as environmental, the geometry to be realized according to the required service function, the material and the manufacturing process, Fig. 1 [1] . These interactive parameters are matched together by reliability and safety concepts while in this paper, the relation between reliability and safety in fatigue design, Fig. 2, will be highlighted through the example of K-nodes used in energetic offshore constructions, Fig. 3 and 4. D ESIGN CONCEPTS FOR OFFSHORE K- NODES AND PREREQUISITES he most commonly applied fatigue design concepts [2] for the assessment of welded joints, are displayed in Fig. 5. Design prerequisites for evaluating the durability of K-nodes, such as geometry, spectrum, experimental results, allowable stress ranges, fracture mechanics data, FE-model, and the FE-calculation of hot-spot and notch stresses, will be presented. After this, the evaluation of the experimental results by selected concepts will be carried out. Figure 1 : Influencing parameters of durability of welded structures. T T