In cold-formed steel building construction, there are several applications where built-up box sections made of a C-shape nested with a track section, with screw fastenings, are used to resist loads induced in a structural member; when a single section is not sufficient to carry the design load. The cold-formed steel box section may be subjected to eccentric loading when the web of one of the sections receives the load and transfers it through the connection to another section. There may be an unequal distribution of load in cold-formed steel built-up box assemblies loaded from one side. In the current North American Specification for the Design of Cold-Formed Steel Structural Members (CSA, 2002), there is no guideline or design equation to calculate the flexural capacity of this type of section. Cold-formed Steel Framing Design Guide (AISI, 2002) has recommended that the moment resistance and moment of inertia of the built-up sections can be taken as the sum of the two components; based on deflection compatibility of the components. However, this design approximation has yet to be justified by experimental or numerical study especially for the case of eccentric loading. Therefore, a research project involving finite element analysis was undertaken to investigate the flexural behaviour of built-up box sections assembled from cold-formed steel C-shape and track sections when subjected to eccentric loading. The proposed finite element model of the built-up box sections was validated with the tests carried out by Beshara and Lawson (2002). The ultimate moment capacities obtained from the finite element analysis were then compared with the predictions from the current design method; in order to asses its suitability. Parametric studies were carried out to identify the factors affecting the flexural capacity of built up cold-formed steel box sections.
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