Bracing Stiffness and Strength in Sheathed Cold-formed Steel Stud Walls

The objective of this paper is to provide the stiffness and strength characteristics for coldformed steel stud walls stabilized by sheathing. The primary stability resistance is provided by translational (lateral) stiffness supplied at the fastener locations to the cold-formed steel studs. This paper separates the source of this translational stiffness into two parts: local and diaphragm. To analyze the local stiffness an experimental study consisting of small-scale stud-fastener-sheathing assemblies is conducted. In these tests sheathing type, stud spacing, fastener spacing, edge distance, environmental conditions, and construction flaws are all varied. The results provide characterization of the local stiffness and strength that is supplied as the fasteners bear and rotate in a stud-sheathing assembly. Results are sensitive to the design variables (stud, fastener, sheathing, spacing) as well as the environmental and construction conditions. Diaphragm stiffness develops as the sheathing itself undergoes shear, which also translates into a lateral resistance at the fastener locations. A simple analytical model for the translational stiffness supplied by the sheathing diaphragm action is proposed and validated. The importance of including both local and diaphragm stiffness is illustrated with a test on a full-scale cold-formed steel stud wall. For the first time, this paper provides a comprehensive bracing model for sheathing-braced stud walls which include both local and diaphragm stiffness.