Experimental study of the cross-sectional capacity of cold-formed steel built-up columns

This paper describes a comprehensive experimental programme in which built-up cold-formed steel stub columns with four different cross-sectional geometries were investigated. Twenty built-up sections were fabricated from individual channels and flat plates with nominal thicknesses ranging from 1.2 mm to 2.4 mm and assembled with either bolts or self-drilling screws. The connector spacing was varied among specimens of the same geometry in order to study its effect. The built-up columns were tested between fixed boundary conditions and the load was transmitted through end plates which were attached to the columns with an epoxy resin. Tensile coupons were taken from the corners and flat portions of the constituent sections in order to determine their material properties, while detailed measurements of the geometric imperfections of each specimen were also performed using a laser displacement sensor. The experiments revealed a significant amount of restraint and interaction between the individual components of the columns while buckling, with the connector spacing having a pronounced effect on the observed buckling modes. However, the ultimate cross-sectional capacity was seen to be much less dependent on the connector spacing within the considered range of spacings.