Evaluating System of Applicability of High Strength Steels

在本项目中，开发了一套船舶结构用高抗拉强度钢的有效性评估系统。重点介绍了通过焊接连接到纵梁和横梁上的桥面板。在这种焊接结构中观察到焊接初始缺陷。为此，建立了一套系统的含焊接缺陷壁板极限强度的估算方法。它由两个阶段组成。在第一阶段，当指定焊接条件时，估计焊接缺陷，如初始挠度和残余应力。在此基础上，从理论上计算了初始挠度的有效系数。然后，在第二阶段，可以用一个简单的公式来估计板材的极限强度。因此，通常使用HT系数来衡量高抗拉强度钢相对于低碳钢的有效性。Th因子定义为高强度S…的相对厚度与具有相同极限强度的软钢相比，具有更高强度的钢板。针对HT32和HT36两种钢，利用实际焊接条件，估算了宽高宽比壁板的焊接初始缺陷。在此基础上，利用上述公式计算了含这些缺陷的板材的抗压强度，并根据NK准则计算出腐蚀裕度为2.5 mm。计算腐蚀裕度的高温系数也可以用来评价高抗拉强度钢的有效性，但对于加筋板，不能像在单板情况下那样简单地用高温系数来评价高强度钢的有效性。这需要对所考虑的结构的倒塌机制和极限强度进行仔细的研究。为此，提出了一种效率优于普通有限元的理想加筋板单元。较少

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