Proposal to Improve the DSM Design of Cold-Formed Steel Angle Columns: Need, Background, Quality Assessment, and Illustration

This paper presents a proposal for the codification of an efficient design approach based on the direct strength method (DSM) for cold-formed steel equal-leg angle columns with short-to-intermediate lengths, i.e., those buckling in flexural-torsional modes. Initially, the available experimental failure load data consisting of fixed-ended and pin-ended (cylindrical hinges) columns with several geometries (cross-section dimensions and lengths) and tested by various researchers are collected. These are used to show that the currently codified DSM design provisions are not able to handle adequately short-to-intermediate angle columns and that a specific DSM-based design approach is needed to estimate the failure loads of such columns. Then, the paper presents a brief overview of the structural reasoning behind the proposed DSM-based design approach. Next, the quality (accuracy and reliability) of the failure load estimates obtained with this design approach is assessed through the comparison with the aforementioned experimental failure load data and also a fairly large number of numerical failure loads previously obtained by the authors. This merit assessment includes the determination of the load-resistance factor design (LRFD) resistance factors concerning the failure-to-predicted load ratios. It is shown that the value recommended for compression members by the North American specification, phi c=0.85, can also be adopted for short-to-intermediate angle columns designed with this DSM-based approach. Finally, the paper presents and discusses a few numerical examples that illustrate the application of the proposed design approach and provide evidence of its user-friendliness and advantages/benefits when compared with the currently codified one.