Numerical investigation of the impact of bearing condition on the axial behavior of variable-height cold-formed steel stud wall assemblies

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This paper is devoted to identifying and numerically characterizing the strength of cold-formed steel (CFS) wall assemblies of various height with non-uniform bearing conditions. The results are for a means of evaluating existing design guidelines presented in the North American Specification of the American Iron and Steel Institute (AISI S100-16). In this standard, the bearing condition of the members is not included in equations for predicting axial strength. However, based on the recent experiments done by the authors, non-uniform stress distributions at the ends of CFS studs, caused by different bearing conditions, can reduce the axial capacity of the assemblies. The sources of nonuniformity considered were finite flexibility of the concrete slabs, uneven bearing surfaces provided by the slabs, distance of the wall assemblies to the slab edge, or overhang conditions caused by construction error. In the experiments done by the authors, the height of lipped-channels was fixed to 12 inches to enable comparison across specimens. However, in typical construction, wall assemblies installed on concrete slabs are generally full-height (8 ft or higher) and thus globally-dominant. In this paper, various heights are considered for the studs. They are determined based on the local, distortional, and global buckling half-wavelengths. The impact of bearing conditions on the strength is further elucidated via high-fidelity 3D finite element analyses (FEA). The results of FEAs clarify how the non-uniform stress distribution at the ends of the studs or partial bearing conditions can impact their strengths when they buckle locally, distortionally, and globally. The finite element models are calibrated with existing experimental results. Comparison to available experimental results and to the governing design codes are provided.