Finite element comparison of design methods for locally slender steel beams and columns

The objective of this paper is to describe and analyze a series of nonlinear finite element analyses used to compare three design methods for locally slender, braced, steel beams and columns. The three design methods are: (i) the hot-rolled steel AISC Specification, (ii) the cold-formed steel AISI Specification which uses the effective width method throughout, and (iii) the cold-formed steel Direct Strength Method which was recently adopted as an alternative design method in the AISI Specification. To aid the comparison of the available methods the design strength formulas, for locally slender W-section beams and columns, are provided in a common notation. The resulting design expressions highlight the prominent role of elastic cross-section stability as the key parameter for strength prediction. The comparison for beams shows that the AISC and AISI methods take very different approaches to predicting the strength of locally slender sections. A nonlinear finite element analysis parameter study, using ABAQUS, is initiated for the purpose of understanding and highlighting the parameters that lead to the divergence between the capacity predictions of the different design methods. Particular attention is placed on understanding the regimes where the AISC methods give divergent results, from either the other Specifications, or the nonlinear finite element analysis results