The Study Of Limit State For Jacket

Jacket is one of the main ocean engineering structures in oil development at the sea, with the development of the offshore oil production, more and more jackets are used. Jackets may be affected by different loads when they are work, such as the load of ice. So it is important to analyze the limit state and get the maximal load of the structure.The basic task of the structure limit analysis is to calculate the structure bearing capacity, which provides the essential, reliable basis for the determination of structure safety tolerance. The anti-load capacity is full used in the plastic limit analysis method. The paper provides a method to calculate the limit load which uses of adding spring element for the first time. It is based on the theory of plastic limit analysis.This paper introduces the adding spring element method by ANSYS, and calculates the limit load for a jacket. At first, the method will add COMBIN40 element at the place where maybe produce a plastic hinge. The next step, we will apply load to the structure and do elastic analysis. Then we multiply the result of the elastic analysis by plastic adaption coefficient of cross—section to simulate the structure's full plastic state. The plastic hinges come into being one by one. At last, we can get the limit load and the destroy structure.This paper applies another method to calculate the limit load of the same jacket. The method uses the BKIN function in ANSYS. And the load consists of many sub-steps. When the result of one sub-step isn't convergence, the load is the limit load.