Study on the Lateral-Torsional Buckling of Duplex Stainless Steel Welded I-Section Flexural Members
试验中除S-DI-150-3000发生局部-整体相关屈曲外，其余构件均发生侧向弯扭屈曲破坏，将试验结果与欧洲规范和中国规范预测值进行对比，结果表明：上述规范的预测值均偏于保守，试验值与计算值比值的均值分别为1.23和1.18；所建立的有限元分析模型可以准确预测构件的承载力，试验值与计算值比值的均值为1.06；基于参数化分析结果和不锈钢材料的特点，建立了两阶段的受弯构件整体稳定承载力的计算公式，当正则化长细比不小于0.54时，采用改进的Perry公式表达正则化长细比与稳定系数之间的关系；当正则化长细比小于0.54时，近似采用线性方程表达两者的关系；在此阶段构件稳定系数大于1.0，以抗拉强度与屈服强度的比值作为最大值，充分利用不锈钢材料屈服后显著应变强化的特征。将试验数据与所提公式的计算值进行对比表明：该方法具有较高的精度，试验值与所提公式预测值的比值均值为1.0，标准差为0.11。Abstract: Stainless steel structure has good mechanical properties and excellent corrosion resistances, which is one of the best choices of the structural schemes for important infrastructures in highly corrosive environments. Related researches on stainless steel structures began from 1960s, and have grew rapidly in the past 20 years as the more and more attentions have been taken to the durability and the safety of structures. Currently, researches on stainless steel structures mainly focused on the material properties and the performance of cold-formed members, while the researches on the behavior of the stainless steel welded members were rare. Besides, the material characteristic of stainless steel has not been fully incorporated into the design method. This study would report an experimental study on the lateral-torsional buckling of duplex stainless steel welded I-section flexural members, and modify the related design formula to include the material properties characteristic of duplex stainless steel.
Firstly, a four-point bending test rig with the strong constraints at the loading points was proposed for the lateral-torsional buckling test in this study. In this test rig, to clarify the boundary conditions and reduce the possible redundant constraints from the test rig applied to the test specimen, the lateral constraints were configured at the same location as that of the loading points, which was different from the traditional test rig that following the concept to release the constraints at the loading points. A series tests were then conducted for seven flexural members to obtained full set of test data, including the initial geometric imperfection, the material properties, and the failure mode and capacity. The test data was compared with the predictions of Eurocode and Chinese code. Finite element models of the welded stainless steel flexural members were established and verified by test data, and then parametric analysis were carried out. Based on the results of parametric analysis, the design formulas for the lateral-torsional buckling were modified considering the strain hardening characteristic of stainless steel.
All the specimens showed the lateral-torsional buckling except the S-DI-150-3000, which had the local-global interaction buckling. Comparisons between the test data and the predicted values of the Eurocode and the Chinese code showed that the predicted values of the two design codes were both conservative. The mean ratios of the test values over the predicted values were 1. 23 and 1. 18, respectively. The finite element model can accurately predict the bearing capacity. The mean ratio of the test values over the bearing capacity obtained by finite element analysis was 1. 06. Based on the analysis results and the characteristic of stainless steel, a two-stage formula was established. When the slenderness was not less than 0. 54, the modified Perry formula was used to express the relationship between the slenderness and the reduction factor. When the slenderness was less than 0. 54, a linear relationship between the slenderness and the reduction factor was approximately employed. To make full use of the characteristic of considering strain hardening after yielding, the reduction factor was allowed to be greater than 1. 0 with the maximum value of the ratio of the tensile stress over the nominal yield stress. Comparisons of the test data and the predictions of the proposed formulas showed that the proposed formula can accurately predict the bearing capacity. The mean ratio of the test values over the predicted values was 1. 00, with a low scatter of 0. 11.
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