Abstract:Five hundred and sixty eight test coupons taken from thirty coldformed thickwalled steel square and rectangular tubes with different sizes of sections, thickness of plates, grades of steel and different manufacturers were tested to investigate the effects of coldforming process on the material properties of different parts of sections. The test results indicate that the coldforming effects have obvious influence on the strength and ductility of coldformed thickwalled sections. The difference of material properties between two adjacent plates connected to the plate containing weld can be ignored. The yield and tensile strength of weld portion and corner parts are enhanced compared with the adjacent plates. The yield strength enhancement factors of corner parts increase with the increase of the ratio of the length of centerline to the inside diameter of corners, but the enhancement factors for tensile strength are independent on the respective parameters. Based on the investigation, distribution patterns of yield strength, tensile strength, tensile to yield ratio and percentage elongation of coldformed thickwalled steel rectangular hollow sections were proposed, which can be used for strength and stability analysis of corresponding beams and columns, while the coldforming effects are to be taken into account.

Abstract:Sixteen specimens were tested under axial compression to investigate the effect of coldforming process on the behavior of stub columns. The main parameters varied in the tests were the widththickness ratio of steel tubes. The test results indicate that the shape of loaddisplacement curves depends mainly on the widththickness ratio of crosssections. When the widththickness ratio is relatively small, the axial load decreases slowly after the peak ponit of the curve and the total axial displacement is relatively large before failure. On the contrary, the effect of local buckling on the loaddisplacement curves is significant, which results in the sharp declining of curves after the peak point when the withthickness is rather large. Meanwhile, the calculation results of related standards considering the coldforming effects were compared with the experimental results. The comparison show that the formula for calculating the yielding strength of coldFormed thinWalled sections considering the coldforming effects in Chinese Technical Code of ColdFormed ThinWalled Steel Structures(GB500182002) is suitable for those coldformed thickwalled steel stubs with local buckling restrained.

Abstract:In order to investigate the coldforming effect on yield strength distribution of coldformed thickwalled steel with open section, coupon test and axial compression test were carried out. Firstly, 5 types of coldformed lipped channel sections with thickness of 3, 8, 12 and 16mm, and two yield strength grades of Q235, Q345 were chosen to conduct coupon test for the web, flange, curling, corner parts, respectively, and a corresponding distribution model for the yield strength distribution of coldformed thickwalled steel with lipped channel section was put forward. Then, the axial compression tests of 5 stub columns with the same section as the coupon test were carried out for further investigation on the coldforming effect. Finally, the results of stub column test, the results based on the proposed yield strength distribution model, and the results based on the related codes in various countries were compared. It is shown that, the yield strength distribution of coldformed thickwalled steel with open section is greatly influenced by the coldforming effect, and mainly depends on the width to thickness ratio of the plate involved; the estimation based on the proposed yield strength distribution model is close to that based on of the codes in various countries, as well as the test results, although the latest is slightly larger. Moreover, among them, the results based on the Chinese code, GB 50018—2002, is closest to the experimental values with smallest variation coefficient, which means a best applicability.