Behavior and Design of Sheathed Cold-Formed Steel Stud Walls under Compression

Currently, there is a need for a design method for cold-formed steel (CFS) stud and track walls that use traditional sheathing materials to brace against compressive load. The objective of this paper is to provide a robust design method for these walls. Existing design methods are unable to handle dissimilar sheathing attached to the CFS stud flanges [e.g., oriented strand board (OSB) on the exterior face and gypsum board on the interior face] and provide no clarity on the impact of key properties including sheathing shear rigidity and stud spacing. A series of tests on axially loaded sheathed single studs and sheathed full walls using OSB, gypsum board, or an unsheathed face (and combinations thereof) is performed to elucidate the basic behavior and limit states. The stiffness that the fastener-sheathing system supplies to the stud as bracing is characterized analytically and experimentally. The characterization clarifies how both local fastener deformations and global sheathing deformations contribute to sheathing bracing. The impact of sheathing on elastic stability of the stud in local, distortional, and global buckling modes is provided. Both computational and analytical methods for stability determination including bracing stiffness from sheathing are detailed. An extension to current design methods that uses the enhanced elastic stability provided by sheathing bracing is proposed for member strength prediction. The design method is shown to agree well with the performed tests, providing consistent predictions for the limit state and the strength for walls with sheathing, including sheathing on one side only, and dissimilar sheathing on the two stud flanges.