Experimental investigation into the behaviour of back-to-back gapped built-up cold-formed steel channel sections under compression

摘要

Back-to-back gapped built-up cold-formed steel channel-sections are used as compression members in cold-formed steel structures, such as trusses, space frames and portal frames etc. Because of the complex and non-uniform cross section of the back-to-back gapped built- up cold-formed steel channel columns, it is difficult to calculate the strength of these sections accurately. Current guidance by the direct strength method in the AISI Specification and the 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 have been reported for such columns and specially investigated the effect of link-channel's spacing on axial strength of such columns. This issue is addressed herein. Forty new experimental results are reported, conducted on back-to-back gapped built-up cold-formed steel channel-sections, covering stub to slender columns. Axial capacity of the columns, load-axial shortening, load-axial strain, failure modes and deformed shapes were observed and reported in this paper. Also, the effect of link-channel's spacing on axial strength, is investigated. Test strengths are compared against the design strengths calculated in accordance with AISI and Australian/New Zealand standard for cold-formed steel 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.