STUDY ON PLATE GROUP EFFECTS AFTER LOCAL BUCKLING OF COLD-FORMED STEEL COMPOSITE COLUMNS
To clarify the plate group effects after local buckling of cold-formed thin-walled steel(CFS)double-leg closed composite columns,this study conducts axial compression tests on 18 CFS double-leg closed composite col-umns formed by connecting single-leg C-shaped and U-shaped sections with ST4.8 self-tapping screws.The tests provide insights into failure characteristics,ultimate bearing capacity,and the deformation of individual plates dur-ing the elastic and post-buckling stages.Results show significant local buckling in the early loading stages.As the load increases,the composite columns enter the post-buckling phase,with plate group effects still influencing the deformation,causing the buckling direction of the C-shaped and U-shaped section flanges to align,demonstrating coordinated buckling.However,this buckling is no longer linear.Based on the experimental results,the study veri-fies the Direct Strength Method(DSM)as outlined in China's GB 50018-2016 and the American AISI-S100-2012 standards.The findings reveal that both methods do not account for the non-linear behavior after local buck-ling,resulting in errors.Specifically,as the width-to-thickness ratio increases,GB 50018-2016 becomes increas-ingly conservative,while DSM results become progressively less safe.