Compression Tests of Cold-Reduced High Strength Steel Sections. I: Stub Columns

This paper describes a series of compression tests performed on stub columns fabricated from cold-formed high strength steel plates with nominal yield stress of $550\mathrm{MPa}$. The steel is classified as G550 to Australia Standard AS1397. The test results presented in this paper are the first stage of an Australian Research Council research project entitled “Compression stability of high strength steel sections with low strain-hardening.” The tests include lipped-square and hexagonal sections, including 94 box-shaped fix-ended stub columns. The purpose of these tests was to determine the influence of low strain hardening of G550 steel on the compressive section capacities of the column members. The results of the successful stub column tests have been compared with the design procedures in the Australian/New Zealand Standard for Cold-Formed Steel Structures and recent (1999) amendments to the American Iron and Steel Institute Specification. As expected, the greatest effect of low strain hardening was for the stockier sections where material properties play an important role. For the more slender sections where elastic local buckling and postlocal buckling are more important, the effect of low strain hardening does not appear to be as significant. This is contrary to recent design proposals in the USA where it was proposed that the more slender sections would be more greatly influenced by low strain hardening. A simple proposal for improved design capacity is given in the paper. A second companion paper (Part II) describes a series of compression tests on long columns made from the same material.