A Study on Ultimate Strength of Folded Steel Plate Girders.

本文研究了在强轴端弯矩相等的情况下，由折叠腹板和翼缘板组合的钢板梁的稳定强度。本文比较了开腹板和折腹板工字钢梁的试验抗屈曲性能。试验结果表明，折叠腹板梁的抗屈曲能力高于普通工字梁。采用基于几何和材料非线性等参壳单元的弹塑性有限元分析方法，分析了由于焊接引起的初始挠度和残余应力而产生初始缺陷的折叠钢板梁的极限承载能力。假设材料本构关系遵循Von Mises屈服准则和plantl - reuss塑性流动准则，结合材料与几何不变性规律、应变硬化规律和线性卸载规律。根据Newton-Raphson和更新的拉格朗日公式（其中位移逐步增加），对其非线性行为进行了数值求解。实际测量了初始缺陷的残余应力和初始挠度。试验结果与分析结果的比值在0.98 ~ 1.028之间，平均值为0.996。由此可以得出结论，该分析方法对于计算折叠钢板梁的极限承载能力是比较准确的。采用非线性有限元方法进行参数化研究，评价了折叠角、板宽厚比、梁长细比、残余应力和屈服应力比对折叠钢板梁极限强度的影响。本文还提出了基于参数化研究的折叠钢板梁失稳分类方法。确定了三种屈曲模式，即非弹性侧扭屈曲模式、非弹性局部屈曲模式和两者的相互作用屈曲模式。通过参数化研究，得出了折叠腹板单元对折叠钢板梁极限强度的影响。少

In this research, the stability strength of steel plate girders assembled by folded web plates and flange plates under equal end moments about their strong axis are investigated. This paper compares experimental buckling resistances of I-shaped steel girders having unfolded web plates with those of the folded plates. The tests show that the buckling resistances of the girders with folded webs can be higher than those of conventional I-shaped girders.To analyze the ultimate carrying capacity of folded steel plate girders with initial imperfections due to initial deflections and residual stresses caused by welding, an elasto-plastic finite element analysis was used based on geometric and material non-linear isoparametric shell elements. It was assumed that material constitutive relationship follows the Von Mises yield criterion and the Plandtl-Reuss plastic flow rule, combined with material and geometric invariance law, strain hardening law and linear unloading law. The non-linear behavi … More or is solved numerically according to both the Newton-Raphson and the Updated Lagrangian formulations where the displacements increase step-by-step. Actual measurements were used for the initial imperfections of residual stress and initial deflection. The ratio of the test results to analysis results for the ultimate carrying capacity is between 0.98 and 1.028, with an average of 0.996. Thus, it may be concluded that this analysis is quite accurate in evaluating the ultimate load carrying capacity of folded steel plate girders.A parametric study using nonlinear finite element approach is also conducted to evaluate the effects of folded angle, width thickness ratio of plate, slenderness ratio of beam, residual stress and yield stress ratio on the ultimate strength of folded steel plate girders. This paper also presents the instability classification of folded steel plate girders based on the parametric study. Three buckling modes are confirmed, i.e., an inelastic lateral-torsional buckling mode, an inelastic local buckling mode and an interactive buckling of the two. From a parametric study, it appears that the effects of folded web element on the ultimate strength of folded steel plate girders. Less