Materials properties of thick-wall cold-rolled welded tube with a rectangular or square hollow section

In order to determine the behavior of thick-wall cold-rolled steel sections with square and rectangular hollow cross-section, experiments concerning materials properties of the flat coupons, corner coupons, parent plate coupons and stub columns were carried out. Effects of cold forming process on material properties were investigated. The stub column test strengths were compared with the compressive strengths determined by the Australian/New Zealand and Chinese standards for designing the cold-formed steel structural members respectively. It has been shown that both strengths predicted by the Australian/New Zealand standard using material properties obtained from the flat coupon tests and strengths forecasted by the Chinese standard based on the mean design yield stress of the full section are quite conservative. The mean design strength determined by the Australian/New Zealand standard using the average design yield stress of the full section is just identical to that predicted by the Chinese standard based on material properties obtained from the flat coupon tests. The latter two design processes are preferable to the present steel tubes because safety and economical efficiency are both attainable. Coarse grains and Widmanstنtten microstructure formed in welded joints contribute to high strengths and low plasticity of the flat specimens with welding seams.