Comparison among simplified procedures for fatigue assessment recomended by classification societies rules

A Unified Recommendation for the fatigue assessment of ship structures (UR56) was issued by IACS in 1999, providing a common framework for fatigue checks by the member Class Societies. UR56, however, while setting a general background for this kind of verifications, does not describe a detailed procedure. Accordingly, the various Societies developed procedures that differ to some extent from each others as regards the various steps of the computation. The paper compares fatigue checks recommended by Rules and Guidelines, with the aim of assessing the sensitivity to input parameters, as well as differences and capabilities in the adopted criteria. A comprehensive test case, represented by a side shell longitudinal intersection with primary supporting member, has been analysed, calculating the fatigue life step by step, as far as possible. Differences have been found not only in the final results, but also in the assessment of the various intermediate quantities (reference loads, reference probability level, way of combining the different components of loads/stresses, type of final verification, et cetera)