Cross-sectional capacity of octagonal tubular steel stub columns under uniaxial compression

Abstract

This paper presents an experimental investigation on the compression behaviour of cold-formed octagonal, circular and square tubular steel stub columns. Three octagonal hollow steel tubes were examined under axial compression while three circular steel tubes and two square steel tubes were tested for comparison. Nine existing test data on octagonal hollow steel tubes were also collated for comparison. The hollow tubes were fabricated by welding two cold-formed half-section steel plates. To examine the material characteristics, flat, curved and corner coupons were extracted and tested. Residual stress distribution in longitudinal direction was also measured by sectioning method. Fifty longitudinal strips with a nominal width of 10 mm were machined by a wire cutting machine. The test results obtained from the tensile coupon tests and residual stress measurements were examined to evaluate the effect of the fabrication process on different cross-sectional shapes. The geometric imperfections of each specimen were carefully measured. Cross-sectional capacity, load-deformation relationships and failure modes of the stub columns were presented by the stub column tests. Finite element model was developed and validated against the experimental results. The experimental cross-sectional capacities were accurately predicted by the finite element models. The test data accompanied with the FE results were assessed with reference to current design provisions on cross-section classification and a suggested cross-section slenderness limit and an alternative design approach for octagonal cross-sections were proposed.