Flexural strength of cold-formed steel joists with reinforced web openings

The floor joists of cold-formed steel (CFS) structures often require large web openings. Reinforcement of such openings may mitigate the detrimental effects of such web openings. This paper is based on an experimental investigation that considered 203 mm deep (base thickness 1.89 mm) galvanized, lipped channel sections with circular, square, and rectangular openings and two associated reinforcement schemes (screw fastening of 31.8 mm × 1.1 mm thick bridging channel). Since the focus of this investigation was on the flexural strength of such joists, the test specimens were simply supported and were subjected to two equal point loads at equal distance from the supports. Two lipped channel sections were set face-to-face to form the test specimen assembly. Based on 11 sets of three identical flexural tests, it was determined that (i) the tension zones of the web with a large opening need not be reinforced, (ii) closely spaced screw fastening of reinforcements (bridging channel) is essential, and (iii) the reinforcements need to be fastened as close as possible to the compression edges of the opening to minimize local buckling of these edges. This paper demonstrates that it is possible to establish cost-effective reinforcement schemes for CFS sections with large web openings.Key words: cold-formed steel, joists, flexural strength, web openings, reinforcements, experimental.