Fatigue life calculations have been recently introduced as explicit checks in classification societies rules for shipbuilding. Such checks are based on the classic S-N approach, which cannot be easily applied to the condition assessment of structural details. Fracture mechanics approach allows describing the structural degradation of ageing structures and the reliability framework accounts for the inherent probabilistic aspects of fatigue. This approach gains relevance as many ship tankers are being converted to operate as offshore ships. This paper carries out a sensitivity analysis of the reliability model for fatigue life calculations of typical ship's welded joints based on fracture mechanics, aiming to select the most influencing parameters, before and after inspection updating. Most important parameters are those related to load effects: unfortunately their knowledge is affected by large uncertainties. It is worth noting that the model is affected by uncertainties of the loads more than 60%. Material parameter C is also quite dominant. Since better knowledge about acting loads is quite difficult to be obtained, it seems that this is an area to improve in order to achieve more confident prediction models. Importance factors do not vary so much before updating. After updating the inspection time and quality has a dominant importance (up to 80% for bracket toe) but rapidly decreasing in time while load parameters (In A and B) correspondently increase their importance. Only for the last inspection the decrease of the inspection importance does not reach its current value during structure's ageing, because the end of life occurs. The quality of inspection appears to be a key-point together with the loads definition and conclusions agree with common sense and engineering judgment; however a few outcomes appear to be useful to make more efficient surveys of ship structures, showing which input need to be less uncertain.


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    Title :

    Fatigue crack growth assessment of welded joints in ships structures: A reliability-based sensitivity study


    Additional title:

    Bewertung der Ermüdungsrissausbreitung in Schiffbauschweißnähten: Eine zuverlässigkeitsbasierte Empfindlichkeitsuntersuchung


    Contributors:


    Publication date :

    2006


    Size :

    8 Seiten, 11 Bilder, 1 Tabelle, 26 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English






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