Interaction between chord compactness and lacing slenderness in CFS built-up columns

Abstract Axial load-resisting capacity of a cold-formed steel (CFS) built-up laced column primarily depends on the unbraced chord slenderness, slenderness ratio of lacings, overall slenderness ratio, and geometry of column sections. Unlike hot-rolled steel built-up columns, current design guidelines do not provide the limiting values of the above parameters for CFS built-up columns. In this study, a numerical study has been conducted to investigate the influence of chord compactness, lacing slenderness and global column slenderness on the behavior of CFS laced built-up columns composed of four unstiffened angle chord members. Finite element models of 144 nos. of built-up columns have been developed in a computer software ABAQUS considering the local and global imperfections. Overall slenderness ratio of CFS columns is varied in the range of 20–180, whereas the chord compactness ratio is varied between 15 and 40. In addition, four different values of lacing slenderness ratios are considered for all built-up CFS columns. The predicted peak strengths of built-up columns are compared with the unfactored axial strengths computed in accordance with the design provisions of North American and European Standards. Based on the findings of this study, a relationship between the limiting values of chord slenderness and lacing slenderness ratios has been recommended for CFS built-up columns with unstiffened angle chords. Further, modified expressions have been suggested for the design of CFS built-up laced columns with unstiffened angle chord members having sectional compactness ratios less than or equal to 20.