Development and Experimental Validation of the Direct Strength Method for Cold-Formed Steel Beam-Columns

Abstract

The direct strength method of cold-formed steel member design uses local, distortional, and global cross-section elastic buckling analysis with empirically derived direct expressions to predict member strength. The direct strength method is an accepted design method in national design specifications and enables a unified, robust, and flexible design approach. However, for beam-columns the direct strength method in current design specifications uses simplified linear interaction expressions based on combining the pure axial and bending elastic buckling and strength response. Today, local, distortional, and global elastic buckling under any combination of axial load and bending moments may be readily found using elastic buckling analysis tools such as the finite strip method. Thus, stability may be assessed under the actual combined actions, but new direct strength method expressions are needed to utilize this explicit stability information in determining beam-column strength. In this paper, new strength expressions for each limit state are developed. In addition, the results of beam-column tests performed by the authors and those available in the literature are used to validate the performance of the new proposed direct strength method for beam-columns. The development of the direct strength method for beam-columns has the potential to provide a more mechanically sound solution to the strength of cold-formed steel beam-columns, eliminate excessive conservativeness, and at the same time encourage the next generation of optimized, high-strength cold-formed steel shapes.