||Weicheng Cui, Xiaoping Huang, Fang Wang
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Traditional strength assessment procedure implemented in marine structural design rules is highly experience-based due to the complexity of the structure and its operational environment. With the fast development of computer technology, software and hardware, the possibility to accurately assess the marine structural strength based on the strict principles of mechanics increases. The criteria which allow the direct calculations of loading and strength are often termed as first-principle-based design criteria. However, it is widely recognized that even the latest classification rules for marine structures are still far from the "real" first-principle-based criteria. Important evidence for this statement is that the strength is assessed at different global (hull girder) and local (stiffened panel and welded joints) levels and in different failure modes (yielding, buckling and fatigue). The relationship among them is not taken into consideration and the relative success of this strength assessment procedure is largely based on past experiences. Furthermore, in most of the fatigue strength assessment methods which are S-N curve based, the effects of initial defects and load sequence have been ignored and the damage state has not been specified. These, together with some other factors, lead to large scatter of the predicted fatigue lives. Significant improvements with regard to the fatigue strength assessment methodology for marine structures are required. The effect of fatigue damage on ultimate strength is not considered too. Thus, for existing marine structures operated for certain period, the strength analyzed may not represent the actual strength a marine structure possessed. Risk analysis based on the current strength analysis procedure is then rather uncertain. Inspection and maintenance decisions based on the assessment may not reflect the actual "optimum"...