Design of the buckling resistance of compressed HSS channels

The use of high-strength steels (HSS) has been limited in building constructions. This is mainly because Finnish and many international regulations still do not cover HSS steels. The buckling resistance of cold-rolled HSS channels were studied on the basis of 24 compression tests in a fixed end condition. Three types of columns with different lengths, consisting of three U two C sections and one hat section, were tested. The material yield strength varied from 530 to 610 N/mm2. In addition, 33 other test results, consisting of tests of three C and three hat sections, were studied. These columns were formed by brake-pressing from steels with a yield stregth 220-550 N/mm2. In the main, the flat plates of sections were so slender that the buckling of plate elements occurred before overall flexural or torsionalflexural buckling. In the case of C profiles the buckling of the edge stiffener also became apparent. The test results were compared with the design resistances determined according to Finnish Building Codes (B6 and B7) and Eurocode 3 (EC31Part 1 and EC3/Annex A). The simplified method of the B6 code for torsionalflexural buckling is very inaccurate and in some cases it also gives unconservative results. For flexural buckling, the B6 code is too conservative, specially in cases of relatively slender flat plate elements. The design rules of codes B7 and EC3/ Part 1 give quite good results. It was also observed that the resistances agree even more closely with the test results if the actual stress is used instead of the yield strength when determining the postbuckling capacity of flat plates. Edge stiffeners also have a very good post-buckling capacity. The approximation that the capacity is roughly equivalent to the flexural buckling resistance of an indefinite long column on an elastic foundation was observed to act quite well. The reduction due to stiffener buckling according to B6 gives quite good results but may in some cases lead to slightly unconservative results. The reduction according to EC3/Annex A leads to slightly overconservative resistances. It was also observed that the effect of residual stresses is very significant in the case of small but relative thick cross sections