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Axial compression tests and corresponding finite element analysis were conducted on the basis of material property tests. It was shown that the failure mode of long column with a low width-thickness ratio is global instability, while the failure mode of short column with a high width-thickness ratio is that small bending deformation appeared firstly at the center of the column, then the deformation developed with the gradually increasing load and caused local buckling in the end. The results of finite element analysis can fit well with the test results, which means the feasibility and accuracy can be achieved by using this residual stress model into finite element analysis to simulate the axial compression behavior of cold-formed thick-walled steel members. Then, the finite element model was used based on the collected 26 groups of material properties of different tubes with representative size and thickness to get the axial bearing capacity data of members, and design reliability analysis of cold-formed thick-walled steel members under axial compression was conducted. Finally, the resistance partial factor and the design strength for Q235 and Q345 cold-formed thick-walled steel were proposed for the reference in current revising of related design codes. [ABSTRACT FROM AUTHOR]

In order to investigate the cold-forming effect on the yield strength of cold-formed thick-walled steel sections over 6. 0 mm thick, four cold-formed steel rectangular hollow sections with representative size and thickness were selected to investigate the material properties of different parts of the sections. Meanwhile, existing data of material property tests and short column tests were collected. The modifying formula for yield strength considering cold-forming effect based on different codes in the world were summarized, and the calculation results from those formulas were compared with the test results. It is shown that cold-forming has a strong influence on the yield strength of cold-formed thick-walled steel sections, and it depends greatly on the width to thickness ratio of each plate of the sections. The calculation results of Chinese code, AISI ( American Iron and Steel Institute) standard, Australian/New Zealand standard and the formula proposed by Zhu Aizhu are in conservatively agreement with the test results, while that of Eurocode is a little larger. The suitability of the improved method from Chinese Code was theoretically proved, and it can get a little safer results with a lower coefficient of variation, which means appropriate to be used in practice. [ABSTRACT FROM AUTHOR]