The Reliability Analysis of a Jacket Platform under Ice Loads Based on Respond Surface Method

Abstract

Objective: The jacket platform is made of various types of steel pipes and beams welded, mainly used in shallow water areas, such as Bohai oilfield in China. In winter, the sea area where the platform is located will freeze, and the influence of ice load on the platform can not be ignored. So the influence of ice load on the reliability of jacket platform is studied in this paper. Methods: In this research, the finite element model of the jacket platform was established in the form of beam element, and the loads were applied from different directions to find the load direction with the greatest influence on the platform state. When calculating the ultimate load of the platform structure, it is necessary to carry out nonlinear analysis. Selecting the ice load condition, increasing the ice load step by step on the platform structure. As the applied load gradually increases, the platform will appear nonlinear, then the ultimate load of the jacket platform will be obtain. The pile radius and pile thickness are uncertain components in the reliability study of the jacket platform due to manufacture, processing, and other factors, therefore the values of the pile's parameters are all random. Consider the deviation of geometric parameters with the extreme value type I distribution of ice load, the limit state equation for the strength failure of the platform under ice loads is obtained using Response Surface Method, then the reliability of the platform is calculated by the Monte Carlo method and First Order Second Moment Reliability method. Results: By nonlinear analysis, the ultimate bearing capacity of the platform studied in this paper is about 8000kN. The reliability probability of the platform calculated by Monte Carlo method is 0.9999993, and the reliability index is 4.813. The reliability probability of the platform calculated by the first order second moment method is 0.9999994, and the reliability index is 4.852. Conclusion: The results obtained by the two methods are almost the same, and the reliability index is very large, indicating that the platform can operate safely and reliably under the ice load.