Evaluation of the Composite Action of Cold-Formed Steel Built-Up Battened Columns Composed of Two Sigma-Shaped Sections

Cold-formed steel (CFS) built-up battened columns are employed to obtain a sufficient load-bearing capacity when individual profiles cannot withstand the specified stresses. This sufficient load-bearing capacity can be obtained when the individual profiles present a composite action. This paper presents the optimal layout for CFS built-up battened columns to achieve a high level of composite action between two Σ-shaped CFS profiles. A calibrated finite element modeling technique was used to evaluate the effect of the number of fasteners per batten panel and the distance between the batten panels on the axial capacity of CFS built-up battened columns. The optimal number of fastener rows and the distance between the batten panels were determined using 100 models, in which a high level of composite action was achieved between CFS profiles. Then the maximum axial load-bearing capacity of additional 600 finite element models using the optimal layout was compared with the analytical predictions in the European standard EN1993-1-1. The results recommended four rows of fasteners per batten panel. The results suggested an optimal distance of 30imin between batten panels. The results showed a close agreement between finite element and analytical predictions from EN1993-1-1, following the procedure specified in clause 6.3.1, adopting the modified slenderness ratio from the American Specification AISI S100-16. Reliability analysis was also performed to evaluate the analytical methods by targeting a reliability index of 2.5. The results showed that the analytical prediction following the EN1993-1-1, clause 6.3.1, incorporated with the recommended slenderness ratio from the AISI S100-16, is a reliable analytical procedure for CFS battened columns.