Structural behaviour and design of plywood sheathed cold-formed steel wall systems subjected to out of plane loading

An experimental study was conducted to explore the strength contribution of plywood sheathing boards that are regularly used in the cold-formed steel (CFS) wall panel construction. A series of material tests and 4-point bending full-scale tests were carried out. The testing program includes various key design factors such as sheathing board thicknesses, screw spacings and slenderness of the CFS studs. The test results indicate that the plywood sheathing thickness of 12 mm is sufficient for restraining the lateral torsional buckling (LTB) of the slender CFS studs, which also increased the ultimate moment capacity of the CFS wall panel by a maximum of 150%. However, the improvement in flexural strength varies depending on the local and global slenderness of the CFS wall stud. The spacing between the sheathing-screw connection also significantly influenced the structural contribution of plywood-sheathing. The design calculations were carried out as per the AISI design provisions and latest improvements suggested by the previous research works. The design calculations indicate that the design moment capacity of the CFS wall panel can be increased by a maximum of 48%, and most of the design results are conservative compared to the experimental results. Although, it was found that the modified design provisions of AISI are reliable for the strength predictions, the failure modes predicted greatly varied compared to the experimental results. Therefore, a series of individual sheathing screw connection tests were carried out to discover the key factors that influence the bracing effect of sheathings. On the basis of the results obtained from individual sheathing connection tests, the preliminary modifications that are required for the accurate failure mode predictions are suggested.