Axial response of cold-formed steel closed built-up columns composed of unstiffened channels

The previous research on cold-formed steel (CFS) laced built-up columns are mostly limited to the adoption of single laced pattern, with a few studies discussing doubled laced columns. These outcomes of these studies have confirmed that in addition to the other critical parameters, the lacing pattern also plays a role in governing the behaviour of CFS laced built- up columns. The paper discusses an experimental investigation on the axial response of CFS built-up columns composed of unstiffened channels. Two channels were arranged in the face-to-face orientation and were laterally connected with N- pattern lacing to form a closed built-up section. Self-drilling screws were used to fasten the lacing elements to the chords. The height of the column specimens was 2.4 m approximately and were concentrically compressed between pinned ends. The lateral spacing between the channels and thickness of the lacing element were the two parameters that were varied. The axial response of the specimens was noted in terms of peak loads, load-displacement behaviour and failure modes. Although none of the current design standards bring out design guidelines specifically for CFS laced columns, the adequacy of the design rules meant for CFS built-up columns with closely spaced chords given in the North American Specifications (NAS) and European Code (EC3) for CFS structures was assessed. It was observed that both these standards predict the capacity of CFS laced columns unconservatively. The NAS predictions were unconservative by up to 27% and EC3 by up to 21%