Enhancements to the Direct Strength Method of cold-formed steel member design

Abstract

The design of thin-walled cold-formed steel members must consider various forms of buckling. The Direct Strength Method simplifies strength prediction with a common approach utilizing adaptations of the Winter plate buckling formula. Recent modifications to the Direct Strength Method were developed for flexural members not symmetric about the axis of bending, which introduced a new general form to the direct strength equation. The versatility of this form provides one strength curve for the entire range of slenderness, including inelastic reserve strength. This new form was investigated for local and distortional buckling of compression members, members with holes, beam–columns, and beam–columns with holes. The proposed formulas for members without holes gave strength predictions nearly identical to the current AISI expressions. For members with holes, the proposed strength predictions were compared to test data and showed improvement over the current AISI expressions. Shear buckling strength was also investigated using the new direct strength equation form which gave equivalent predictions. Enhancement to the global buckling strength curve for flexural members was explored for alignment with column buckling and to facilitate further consistency for global buckling of beam–columns. The proposed enhancements provide improvements with a consistent set of simpler equations, advancing a new cleaner appearance to the Direct Strength Method.