Moment capacity of back-to-back cold-formed steel channels with edge-stiffened holes, un-stiffened holes, and plain webs

Abstract The use of cold-formed steel (CFS) back-to-back channels as floor joists is increasing steadily, and such beams often include un-stiffened holes for installation of services, which reduces their flexural strength due to the reduced web area. A new generation of CFS channels with edge-stiffened holes has been widely used. However, no research has been undertaken to understand the effects of composite actions on moment capacity of such built-up beams. In this paper, fourteen new experiments are reported on back-to-back channels with various hole spacing, which were tested under four-point loading. Finite-element models were also established and validated with the experiments. Upon validation, a parametric study involving 63 FEMs was conducted to investigate the effects of beam length, diameter of hole, stiffener length and fillet radius. The test results show that for back-to-back channels with five edge-stiffened holes, the moment capacity increased by 15.4%, compared to that of a plain channel. For comparison, the same section with un-stiffened holes had a 15.1% reduction in moment capacity. Test results also show that distortional buckling was the predominant failure mode for all cases. The test and FE results were compared against the design moment capacities predicted by the American Iron and Steel Institute (AISI) and Australian and New Zealand Standards (AS/NZS) for plain channels. For channels with holes, design procedure was proposed by Moen and Schafer. It is revealed that these equations are conservative by around 23% and 49% for CFS channels with un-stiffened and edge-stiffened holes, respectively.