Experimental and numerical tests of cold-formed square and rectangular hollow columns

This paper summarizes the results of experimental tests and finite element simulations aimed at investigating the buckling response of cold-formed square and rectangular hollow columns. The material stress–strain curves of the tested columns have been derived from testing 83 coupons sampled from the flat and corner parts of the cross-sections, along with coupons containing the weld in both longitudinal and perpendicular directions. The experimental stress–strain parameters have been statistically processed to calibrate the parameters of Ramberg-Osgood and Giuffrè-Menegotto-Pinto material models. The cross-sectional geometry and geometric imperfections have been also measured for all tested profiles. The buckling resistance of 21 different pin-ended columns has been experimentally measured in order to examine the influence of the steel grade (both S275 and S355), the normalized slenderness and the shape of cross-section. Finite element simulations of the tested members have been carried out to investigate the influence of residual stresses and out-of-straightness imperfections on the buckling resistance of hollow profiles. The buckling resistance evaluated on the basis of current EN1993-1–1 and the measured properties of the members are in very good agreement with the tested buckling resistances, even though slightly underestimating the resistance of stocky columns. The partial safety factor for flexural buckling has been evaluated using the method given by Annex D of EN 1990 and the results show that the computed average partial safety factor of curve “c” of EN1993-1–1 for cold-formed square and rectangular hollow columns is 0.92