Ultimate Strength Analysis Of Ship Box Structures Based On Idealized Structural Unit Method

Full life cycle design including security, economy and manufacturability of the shipstructures has been paid great attention to by naval architects. The ultimate strength of shipstructures under extreme loads has become a significant issue.Compared with the conventional methods for ultimate strength calculation, the idealizedstructural unit method which has the advantages of simple model, computational efficiency,good adaptability and accuracy, predicting the ultimate strength of large scale structures, hasbecome an effective tool for evaluating carrying capacity of ship structures, which has beenwidely used in computational analysis of offshore large floating structures such as oil tankers,bulk carriers, container ships, FPSO.The plastic node method is the theoretical basis for the idealized structural unit method.The conventional finite element method is applied in the elastic range, while it is assumed thatplastic deformation beyond the elastic range is concentrated on nodes in the unit. In thetheoretical system of idealized structural unit method, there have been three main kinds ofidealized structural units which are known as ISUM beam-column unit, ISUM plate unit andISUM stiffened plate unit. Behaviors of each ISUM unit during the whole collapse process arederived in detail, including the stress-strain relationship in the elastic range, bucklingevaluation, elastic-plastic stiffness matrix, the evaluation of ultimate limit state, failure modefor units and stress–strain relationship during the post ultimate strength.The calculation procedure for the ultimate strength analysis of ship structures is written.By comparing experimental values with the calculated results from this procedure, typical boxgirder structures are applied and the accuracy of the procedure is verified.Box girder and box column structures are used as calculation cases. Comparativeanalysis of the ultimate strength is presented applying the idealized structural unit method andthe conventional nonlinear finite element method.