Direct Strength Method Study On High Strength Cold-Formed Steel Squared Axial Compression Columns With Stiffened Elements

Cold-formed steel has a tendency to high strength, thin-wall and complex sections. Besides overall buckling and local buckling, distortional buckling is also an existing buckling mode. It is hard to use Effective Width Method (EWM) to calculate the ultimate bearing capacity of high strength cold-formed steel with stiffened elements. However, as a newly developed design method, Direct Strength Method (DSM) takes distortional buckling into consideration and avoids calculating effective width of the complex section for making use of geometric properties of gross section.A total of 32 high strength cold-formed steel squared axial compression columns with section thickness t=0.6mm and a range of lengths from 400mm to 2160mm were calculated by DSM. Comparing the calculated results of DSM with the test results, this paper drew a conclusion that DSM could be applied to calculate the bearing capacity of high strength cold-formed steel squared axial compression columns. The tested section was equaled to squared section with intermediate steiffeners on the web. The bearing capacity of equivalent section specimens was calculated by DSM and the results were compared with the results of test specimens, which further proved the above conclusion.The key point of using DSM is to calculate the local buckling stress f_o1 of the section. Based on the theory of finite strip method, software CUFSM was used to calculate the local buckling stress of the section. After calculating local buckling stress of many squared section members with different width and different height of stiffener, this paper gave a practical formula for the calculation of local buckling stress f_ol of this kind of section through data regression, which could be used as a reference in design calculation.