Ultimate Strength Analysis of Offshore Structures : Application of Idealized Structural Unit Method

Abstract

In recent years, many offshore oil drilling rigs are produced. In order to guarantee their structural strength, it is very important to estimate their ultimate strength by clarifying their plastic collapse behaviors. The authors propose the Idealized Structural Unit Method as a very effective method to analyze nonlinear behaviors (including buckling, plastification, etc.) of large structures. Applicability of the method bas been confirmed by applying formerly developed some idealized structural units to actual problems such as the ultimate transverse strength analysis of ship structures. In this research, the Idealized Structural Unit Method is applied to the analysis of the ultimate strength of offshore structures (jacket type). Firstly, the idealized structural unit is developed for steel pipe members used in offshore structures. Then, its accuracy of idealization is confirmed in the unit member and a simple pipe structure. Finally, the ultimate strength of a full-sized big model of jacket is analyzed in a very short CPU time so as to show the applicability of the method.