High strength and different square sections with axially loaded cold-formed tubular members

This paper studies experimentally tensile coupons and stub columns to quantify the change of mechanical properties by cold forming in scaling factors and strength of axially loaded tubular members in two sizes and of two steel grades. At corners, the enhancement of 0.2% proof strength was about 10% less in high strength steel (HSS) profiles than in their mild steel peers and was about 5% less in smaller profiles than in larger ones as elastic deformations were greater in the smaller or HSS profiles. The ratio of tensile-to-yield strength was between 1.09 and 1.20 for all the studied profiles, satisfying the Eurocode requirements. The strains measured from tensile coupons partly fell below product limit of 3% but from column tests satisfied the requirements. The elastic modulus received from the larger section varied between 195000 N/mm2 and 215000 N/mm2, which were 10-20% more than those from the smaller section. The elastic moduli were reduced if the section was smaller or was made of HSS. A two-stage material model was improved and validated experimentally for the steel grades and section size studied. The equations developed for corner strength predicted well the strength of stub columns with thick walls or smaller sections. The strength of the stub column of the larger profile received by scaling up the strength of the column of the smaller profile needs to be reduced up to 8% because the effects of cold forming depend on the size of the profile. Generally, the changes in values of the yield strength along the circumference of sections need to be considered.