Fatigue Analysis of Jack-up Leg Structures in Transit condition

Abstract

In transit condition, jack-up platform is a type of floating structures with large dimension. In towing duration, legs of the self-elevating unit are elevated, so they do not directly subject to wave and current loads but only resist inertia loads due to motion induced wave and other loads. Actually, fatigue damages of the jack-up legs structure in transit condition have not been studied clearly yet. However, Registers and Consultancy have been used 20% of total fatigue life for transit life time in the analyses and designs [1]. The percentage is approximately value, which has not accurately reflected the fatigue life in transit condition. To have the more accurately results, it is necessary to solve two important problems which are motions analysis and determination of inertia forces on the legs structure induced by the motions. These problems will be made clearly in the article and applied for 400 ft jack-up platform fabricated in Viet Nam.