Compression Strength of Unstiffened Elements in Cold-Reduced High Strength Steel

This paper presents research on unstiffened elements made from high strength G550 steel and subjected to uniform compression. The elements are $1\mathrm{mm}$ or less in thickness and prone to local buckling. Current design rules for these steels specify additional reduction factors to compensate for their reduced strength, which has previously been attributed to the lack of strain-hardening. The paper presents tests and advanced finite-elements analyses of unstiffened elements in compression and identifies appropriate reduction factors for this type of element. The analytical studies demonstrate that the effect of gradual yielding may be the main reason for the relatively low strength of G550 steels in the intermediate slenderness range, rather than the lack of strain hardening. Tests are performed on short single-angle stub columns and on double-angle stub columns. A comprehensive series of material tests of tension and compression coupons is also presented. The test strengths are compared with current American and Australian specifications for cold-formed steel structures, and design recommendations specific to G550 steels are made suggesting that a reduction factor of 0.9 is appropriate for unstiffened plate elements.