In this paper, a fatigue assessment based on spectrum analysis for Jack-up’s legs is performed by adopting stochastic method for three water depths using DNV/SESAM. Firstly, force transfer function is determined by the DNV/WAJAC for each wave direction considered. Secondly, members end stresses are computed by the DNV/SESTRA. Then SCF (stress concentration factors), DAF (dynamic amplification factor) and P-delat effects are applied in the stress range calculations. Finally, the cumulative fatigue damage of unidirectional waves to the critical connections is determined by the DNV/FRAMEWORK. The critical connections at the chords and the braces are selected and reviewed for fatigue life calculation. The results show that the legs have fatigue lives exceeding the expected design life of Jack-Up Drilling Unit of twenty-five (25) years and meet ABS requirement.

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