Performance of reinforced web openings of cold-formed steel joists

The floor joists of Cold-Formed Steel (CFS) structures frequently require large web cut-outs, through which building services may be efficiently located. Presence of a large web opening, however, causes localized redistribution of stresses, and loss of member stiffness and cross-sectional capacities. Providing appropriate reinforcements for such openings may alleviate the adverse effects of such large web openings. The experimental investigation presented in this paper considered the flexural and shear capacities of galvanized lipped channel steel sections having circular and square web openings, and three associated reinforcement schemes. Two lipped channel sections were set face-to-face to form the test specimens. The test specimens were simply supported at their ends, and were subjected to appropriate loads. The plate reinforcement and the stud reinforcement schemes considered in the study are those recommended in the Standard for Cold-Formed Steel Framing- Prescriptive Method for One and Two Family Dwellings. This investigation shows that such reinforcement schemes are ineffective for the joists experiencing high shear. New reinforcement schemes, utilizing bridging channels, were developed for moment regions and for shear regions, and the corresponding responses were experimentally established. The new reinforcement schemes can restore the original flexural capacities and the shear capacities of such sections having large circular or square openings. Overall, it is evident from the test results that it is possible to establish cost-effective reinforcement schemes for cold-formed steel sections having large web openings. Based on this investigation, construction guidelines for web openings reinforcements for cold-formed steel joists have been proposed. © 2013 Taylor & Francis Group, London, UK.