Reinforcement schemes for cold-formed steel joists with a large web opening in the flexural zone: an experimental investigation

The objective of this investigation was to develop an economical and an efficient reinforcement scheme for large web openings in cold-formed steel (CFS) joists in flexural zones that would restore the original moment resistance of the section. This investigation considered commonly used floor joists in North American CFS construction. Tests on joists webs with no openings and with large circular and square openings located at the mid-depth revealed that large openings can reduce the flexural strength by 23%. A reinforcement scheme was established consisting of the screw fastening of bridging channels [38.1 mm × 12.7 mm (1.5″ × 0.5″)] with the same thickness as the receiving joist, along the compression and the tensile edges of the opening, using a screw spacing of 31.75 mm. Three identical tests utilizing the proposed reinforcement scheme restored the corresponding flexural strengths of the CFS section under consideration, and the failure locations were outside the reinforced opening regions.