A novel method for determining the neutral axis position of the asymmetric cross section and its application in the simplified progressive collapse method for damaged ships

Ultimate strength is an important design consideration for the safety of intact or damaged ship structures. The simplified progressive collapse method is a commonly used iterative method to obtain the accurate ultimate strength of ships. Since the accuracy of the neutral axis position directly affects the accuracy of the ultimate strength, the force equilibrium criterion and the force vector equilibrium criterion are adopted to search for the height and angle of the neutral axis, especially for damaged ships. However, the search for the neutral axis position based on the two criteria requires iterative computation which decreases the calculation efficiency. In this paper, the relationship between the results of the iterative process and the neutral axis position is studied, and it is found that the relationship is approximately linear. Then a new iterative method based on the linear equation is proposed to obtain the neutral axis position and is adopted to improve the simplified progressive collapse method. Finally, the new method is used to calculate the neutral axis position of a damaged VLCC. The comparison of the ultimate strength results shows that the improved simplified progressive collapse method based on the linear equation has improved efficiency and good accuracy.