07.15: Experimental and numerical investigation of cold‐formed steel built‐up stub columns

This paper describes a numerical and experimental programme carried out at the University of Sheffield on built‐up stub columns fabricated from cold‐formed steel. A total of 20 built‐up columns with four different cross‐sectional geometries were tested between fixed end conditions. Two of the cross‐sectional geometries were assembled using M6 bolts and the other two using M5.5 self‐drilling sheet metal screws. The connector spacing was varied among specimens of the same cross‐sectional geometry. The cross‐sections were assembled from flat plate, plain channels and lipped channels with nominal thicknesses ranging from 1.2 mm to 2.4 mm. The initial geometric imperfections of each specimen were recorded prior to testing and their material properties were determined by means of tensile coupon tests. Single lap shear tests were also carried out in order to study the connector behaviour of the bolts and the screws used to assemble the specimens.

As part of the numerical part of the study, the test specimens were modelled using the commercially available ABAQUS software package. The recorded geometric imperfections, the measured material properties and the connector behaviour data obtained from the lap shear tests were incorporated into the FE models. Special attention was paid to the connector modelling in order to find an effective and simple way to represent their actual behaviour. The FE models were further used to quantify the effect of the connector behaviour on the buckling response of cold‐formed steel built‐up stub columns.