Bracing for Flexural Buckling in Cold-Formed Steel Framed Walls

The objective of this paper is to explore the flexural bracing requirements in cold-formed steel stud walls using an all-steel design philosophy, i.e., bracing that employs mechanical bridging alone, without sheathing. Bracing strength and stiffness demands in cold-formed steel framed walls must be adequate to ensure safety, but not overly conservative so that the requirements cannot be practically met. The current cold-formed steel design specification, AISI-S100-12, requires the brace for a single compression member to have stiffness equal to twice the ideal brace stiffness, but related proposals for braces in multiple stud walls including brace force accumulation and minimum brace stiffness have not yet been adopted. Elastic critical load and second order elastic analyses are conducted herein to determine an adequate level of stiffness for a single braced compression member, and relationships between strength and stiffness for braced multiple studs to that of a single stud. Statistics of measured member imperfections are incorporated to provide an equivalent imperfection for multiple stud walls. Design by second order analysis is utilized to determine how alternating the direction of studs affects strength and stiffness requirements. For a single braced compression member, the impact of allowing a minimum of 4/3 of the ideal brace stiffness, instead of twice, is explored as an alternative to current requirements. New design expressions for brace stiffness and strength, incorporating the notion of a minimum brace stiffness, and the equivalent imperfection, are provided. The new expressions provide the designer with greater flexibility in developing solutions that meet the necessary stiffness and strength. 

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