Abstract
Abstract This article reports the results of experimental tests conducted on built-up cold-formed steel (CFS) stub columns, composed of double lipped channel members connected with self-drilling screws, which will be applied as the chord members of laced columns. These experiments aim to quantify the effect of four distinct web fastener layouts on the composite action, including the ultimate strength, buckling modes and collapse mechanism for built-up CFS members. The tested stub columns are of 480mm length, double 88x86x40x42x12mm lipped channel cross-section and 0.8mm thickness. The built-up CFS lipped channel members were analyzed with help of the Generalized Beam Theory in order to identify their buckling loads and modes. The Direct Strength Method (DSM) was adopted to obtain the analytical strength of the built-up members, to be compared with the experimental results. The axially compressed built-up members displayed local and distortional buckling, negligible composite behavior and minor effect of number and distribution of the screws. The results indicate (i) inefficient behavior of the self-drilling screws for composite condition purposes and (ii) the DSM rules for non-composite CFS are able to estimate the ultimate strength of this type of built-up lipped channel section.
Highlights
Cold-formed steel built-up sections are applied as structural members in the construction industry for more structurally efficient cross-section shapes, when higher capacity is required
Research conducted by Fratamico et al (2018) indicated that composite action could develop in built-up sections, with axial compression and bending behavior capacity higher than the sum of the individual sections
The main objectives were: (i) quantify the effect of four distinct web fastener layouts on the composite action, including the ultimate strength, buckling modes and collapse mechanism for built-up coldformed steel (CFS) members; and (ii) check the applicability of direct strength method (DSM), as the method does not cover this type of built-up section used in laced columns
Summary
Cold-formed steel built-up sections are applied as structural members in the construction industry for more structurally efficient cross-section shapes, when higher capacity is required. Research conducted by Fratamico et al (2018) indicated that composite action could develop in built-up sections, with axial compression and bending behavior capacity higher than the sum of the individual sections. These authors studied the composite action and the achievable capacities over a range of built-up column crosssection types, practical column end conditions and fastening arrangements for application to CFS framing. The main objectives were: (i) quantify the effect of four distinct web fastener layouts on the composite action, including the ultimate strength, buckling modes and collapse mechanism for built-up CFS members; and (ii) check the applicability of DSM, as the method does not cover this type of built-up section used in laced columns
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