Evaluating System of Applicability of High Strength Steels

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In this project, a system to evaluate the effectiveness of the high tensile strength steel used for ship structures was developed. The main emphasis was put on deck panel which is attached to longitudinal and transverse members by welding. Welding initial imperfections are observed in such welded structures. Therefore, a systematic procedure to estimate the ultimate strength of panels with welding imperfections is developed. It consists of two stages. In the first stage, the welding imperfections, such as initial deflections and residual stresses, are estimated when the welding conditions are specified. Further, effective coefficient of initial deflection is evaluated theoretically. Then, the ultimate strength of the panels can be estimated by a simple formula in the second stage.So called HT-factor is commonly used as a measure to indicate the effectiveness of the high tensile strength steel compared to the mild steel. TH-factor is defined as a relative thickness of the high tensile s … More trength steel plate compared to the mild steel plate which has the same ultimate strength. For two kinds of steels, namely HT32 and HT36, the welding initial imperfections of panels with wide range of aspect ratio are estimated using the actual welding conditions. Further, the compressive strength of the panels with these imperfections are evaluated from the forementioned formula to compute the HT-factors.According to NK rule, 2.5 mm is required as the corrosion margin. HT-factor, which counts for the corrosion margin, can also be computed to evaluate the effectiveness of the high tensile strength steel by following the procedure developed in this project.However in the case of stiffened plate, the effectiveness of the high tensile strength steel can not be evaluated simply by the HT-factor as in the case of single panels. It requires close study of the collapse mechanism and the ultimate strength of the structures under consideration. To this purpose, an idealized stiffened plate element, which is superior in efficiency compared to ordinary FEM, is developed. Less