Testing of CFS double-laced built-up columns: Stability and design considerations

Dar M. A., Sahoo D. R., Ghowsi A. F.

2023 Annual Stability Conference Structural Stability Research Council, SSRC 2023, North Carolina, United States Of America, 11 - 14 April 2023 identifier

  • Publication Type: Conference Paper / Full Text
  • City: North Carolina
  • Country: United States Of America
  • Istanbul Technical University Affiliated: Yes


Cold-formed steel (CFS) members are becoming more popular in building construction owing to their unique features that provide lightweight, cost-efficiency, and fast assembly, ideal for modular construction. As the primary structural members, columns must develop sufficient axial strength and stiffness for adequate functioning. In a typical CFS framing system (used for low-rise structures), built-up columns comprising of two web-fastened channel sections oriented in the back-to-back arrangement (I-type), are used as main compression members. This approach for constructing built-up columns is quite convenient, especially in terms of fabrication simplicity, making it widely adoptable. However, the inefficient sectional configuration in I-type built-up columns restricts the load-carrying capacity that the channels (column chords) can develop if a suitable transverse gap is provided between the same. Previous studies on gapped CFS built-up columns demonstrated that they outperform the traditional I-type built-up columns in terms of axial capacity and stability considerations. Most of the past research on transversely gapped built-up columns has mostly focused on battened columns, and limited research on CFS laced columns has been reported. The limited findings indicated that plain angle sections should not be preferably used as chord members as they are more vulnerable to early local buckling during the initial stages of loading, which results in an early failure at a lower load. Also, the adoption of plain channel sections over plain angle sections as chords in CFS laced and battened built-up columns have displayed a superior performance. However, only single and N-type lacing configurations have been reported. This justifies the need to study further CFS double-laced columns composed of plain channel sections, which has been addressed in the current study. Two plain channels were arranged in a toe-to-toe configuration to form a closed built-up section, with lacing plates adopted as lateral connectors. The transverse spacing between the chords and the lacing slenderness were varied. The effect of these variations on the axial strength and stability characteristics of CFS double-laced columns was assessed, with particular consideration to the lacing and unsupported chord stability characteristics. Lastly, the North American Specification and Eurocode for CFS structures were used to determine the design strengths for comparison. The predictions made by both these standards showed inconsistencies in their accuracy.