The Fatigue Analysis Of Jack-up Platform Jacking Frame

Offshore platform must withstand extremely complex load in service period, it often withstands the high-frequency alternating load, but the elevating gear needs to complete the spud leg and the deck lifting under the fluctuation condition, and also needs sustaining hull deck and equipment in the normal work and the storm condition. Jacking frame is an important component of jack-up platform jacking system. It plays a role of fixing the jacking units and transmitting the load between the main structure and the legs under each kind of the work condition. So there is more possibility that jacking frame appears to be fatigue failure under the effect of thousands tons of horizontal and vertical load. Failure analysis of jacking frame is very necessary.Firstly, the element model of jacking frame is set up, which has been carried on the static analysis under the maximum design load condition. Besides, static strength of the jacking frame is checked according to the structural strength and criterion.Then, the jacking frame has been carried on Transient Dynamic Analysis according to its working conditions. Stress-time response of the jacking frame is received through dynamic response analysis, thus the hazard point is determined as well as stress-time response of hazard point.Finally, based on the dynamic analysis and the disposal of stress-time response of hazard point of the jacking frame, a S-N curve is estimated by the use of theory of the nSoft fatigue analysis and simulation test method .In the history of the jacking frame working hours, their load spectrum blocks are determined for fatigue damage and life of the jacking frame. The analysis method of structural fatigue is practical and simple. It provides some reference value for structure design and safety assessment of the off-shore platform.