Load-carrying Capacity Estimation on Cold-formed Thin-walled Steel Columns with Built-up Box Section

The use of cold-formed thin-walled steel structural members has increased in recent years, and most of their sections are open section with only one symmetrical axis, which would likely fail by twisting and interaction with the others buckling mode, such as local buckling and distortional buckling. To improve the ultimate strength of columns, built-up box section can be used. In this paper, a series of loading capacity tests on high-strength cold- formed steel columns with built-up bo x section are presented, including 21 axially-compressed columns and 19 eccentrically-compressed columns sub- jected to bending moments about weak axis as well as strong axis. The test specimens are built up by two channel sections with two intermediate stiffeners in the web, and they connect at their flanges using self-drilling screws. It was shown that distortional buckling and twisting do not occur and the ultimate load-carrying capacity is 10 to 20 percent higher than the sum of the ultimate load-carrying capacity of each lipped channel section columns. According to the test results and theoretical analysis, an improved method based on the suggestion of current China code ‘Technical code of cold-formed thin-walled steel struct ures’ (GB50018-2002) considering the plate-coupling effect was proposed to estimate the ultimate load-carrying capacity of built-up box section column. With the proposed method, the calculated results are close and conservative to the test results