Abstract:
In Cold-formed steel structures, such as trusses, space frames and portal frames, the use of back-to-back gapped built-up Cold-formed steel channel-sections for column members are becoming increasingly popular. Because of the complex and non-uniform cross section of the back-to-back gapped built- up CFS channel columns, it is difficult to calculate the strength of these sections accurately. Current guidance by direct strength method in the AISI Specification and Australian/New Zealand Standard doesn’t include the gap between the back-to-back channels, thus not being able to predict the axial capacities of these sections accurately. In the literature, very few results are available for such columns and specially investigated the effect of link-channel’s spacing on axial strength of such columns. This issue is addressed herein. The results of 40 experimental tests are reported, conducted on back-to-back gapped built-up CFS channel-sections, covering stub to slender columns. Axial capacity of the columns and load-axial shortening were measured in the tests and reported. The failure modes and deformed shapes were observed. Also, the effect of link-channel’s spacing on axial strength, is investigated. The test strengths are compared against the design strengths calculated in accordance with AISI and Australian/New Zealand standard for CFS structures. It is shown that the design standards can be conservative by as much as 53%, while predicting axial strength of such columns. Therefore, a modification to the non-dimensional slenderness, that considers the gap, is proposed which leads the design standards being within 5% conservative to the test results.
