Study on the Lateral-Torsional Buckling of Duplex Stainless Steel Welded I-Section Flexural Members

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.