This article ,from Structure Magazine, provides a better understanding of the design requirements and methods to laterally brace (bridge) axially loaded cold-formed steel stud walls. Cold-formed Steel (CFS) studs provide a cost effective and extremely efficient structural solution for the typical mid-rise building. In recent decades, CFS design has evolved tremendously as the behavior and design constraints of the material continue to be better defined through comprehensive research and testing. As our understanding of the behavior of CFS studs continues to evolve, the height of a typical mid-rise CFS structure continues to increase. Thus, it is more critical to the integrity of the structure that these heavily loaded studs be adequately braced.
Global buckling of an axially loaded stud can occur in one of three modes: flexural buckling, torsional buckling, or flexural-torsional buckling. Bridging is used within the plane of the wall to prevent global buckling and specific performance requirements of the bridging must be maintained.
The bridging methods described herein represent a mechanical bracing design consistent with an “all-steel design” approach. The all-steel design approach indicates that the CFS studs rely on bridging for stability and that bracing by structural sheathing or gypsum wallboard is not typically considered for axial load stability in the design. One primary reason that CFS walls in mid-rise buildings require an all-steel design bridging approach is that the lower floors may go unsheathed for weeks at a time during construction. Also, for axially loaded walls, it is an industry practice to disregard gypsum sheathing as a structural brace because of durability issues associated with possible water damage. It should be noted that bridging requirements for studs loaded laterally, perpendicular to the plane of the wall, are not discussed herein. Brace forces for studs with combined axial and lateral loading are additive, and the designer is encouraged to refer to The American Iron and Steel Institute (AISI) design guide, Cold-Formed Steel Framing Design Guide (AISI D110-16) where a design example showing the interaction check for combined loading condition can be found.