| Buckling is one of the most important factors affecting steel members' strength. Elastic buckling analysis of typical open cross-section, thin-walled columns have revealed at least three buckling modes: local, overall, and distortional buckling. The distortional buckling is less well known and less well understood. No design rules for distortional buckling exist in Chinese Specification GB50018—2002 . But with the trend to higher strength steel members in cold-formed steel structures, distortional buckling is getting more and more important.The thesis aims at studying the distortional buckling and load carrying capacity of high strength cold-formed steel lipped channel columns under axial compression. The paper includes the following main contents: (1) An experimental research on distortional buckling of high strength steel cold formed lipped channel columns was carried out. The failure behavior and load carrying capacity of the different length and thickness distortional buckling specimens are given.(2) By using material model and geometry non-linear, the distortional buckling and load carrying capacity of high strength cold-formed steel lipped channel columns analyzed by ANSYS are presented. It is agreed with experiments results. The stress distribution changing on whole cross-section is given. The effect of thickness, height, distortional buckling mode, and initial geometry imperfection for high strength cold-formed steel columns on the load carrying capacity is analyzed by non-linear finite element. The different distortional buckling is decided by in-plane buckling of lip of column. (3)Based on the numerical analysis, combined with the Effective Width Method and the Direct Strength Method, a formula is suggested for calculating the load carrying capacity of high strength cold-formed steel lipped channel columns under axial compression.
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