Lateral stiffness and strength of sheathing braced cold-formed steel stud walls

Abstract

The objective of this paper is to provide the stiffness and strength characteristics for walls comprised of cold-formed steel studs stabilized by sheathing. Primary stability resistance for the studs is provided by translational (lateral) stiffness supplied by the sheathing at the stud-to-sheathing fastener locations. 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 a 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, and spacing, as well as the environmental and construction conditions. A simplified and conservative analytical model, supported by more detailed finite element modeling, is also developed, and is appropriate for finding the local stiffness when testing is unavailable. Diaphragm stiffness develops as the sheathing itself undergoes shear, which translates into a lateral resistance at the stud-to-fastener locations. A simple analytical model for the translational stiffness supplied by the sheathing diaphragm action is also 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 that integrates the two forms of lateral resistance: local and diaphragm.