EXPERIMENTAL RESEARCH ON DISTORTIONAL BEHAVIOR OF COLD-FORMED THIN-WALLED Σ-SHAPED STEEL BUILT-UP SECTIONS UNDER ECCENTIRC COMPRESSION

To study the distortional buckling and interactive behavior of cold-formed steel composite sections with Σ-shaped web channels, and evaluate the applicability of current Chinese and North American codes, 22 members were designed and fabricated for compression-bending test. The main parameters including Σ-shaped stiffener, opening position, eccentric compression direction with respect to the strong & weak axis and the eccentricity are investigated to obtain the influence of each parameter on buckling behavior, failure mode and ultimate bearing capacity of the specimen. The test results indicate that all the specimens present distortional buckling or interaction buckling involving distortional mode; The stiffened-web can effectively prevent local buckling of the web; The holes in the web have slight effect on buckling mode; The eccentric compression locations with respect to the strong & weak axis have a significant effect on buckling behaviour of the specimen. Comparing the experimental results with the calculated bearing capacity results according to current Chinese and North American specifications, including GB 50018−2002, JGJ/T 421−2018 and NAS 100−2016, it is found that the calculations with respect to the strong axis adopting Chinese and North American specifications are all conservative; When the specimens are under eccentric compression with respect to the weak axis, the calculated results employing GB 50018−2002 and NAS 100−2016 are both conservative, while the ratio of the test results to the calculation results of JGJ/T 421−2018 averages 1.64, which is too conservative. Therefore, it is proposed that the bearing capacity of eccentric compression with respect to the weak axis should be calculated in accordance with the overall built-up cross-section when the two Σ-shaped channels of composite column work well together.