AbstractTo better understand the mechanical behavior of cold-formed steel (CFS) quadruple-limb built-up box-section (QBB) columns associated with flexural buckling, 12 axial compression tests with different slenderness ratios and screw spacing were conducted. The test results showed that, for a slender specimen (L=2,700 and 3,300 mm), when the screw spacing was reduced from 600 to 300 mm, the load-bearing capacity increased by about 6%–10%. When the screw spacing was reduced from 600 to 150 mm, the load-bearing capacity increased by about 14.6%–17.5%. Arranging end fastener groups can enhance the strength of the column, but it may be cumbersome and uneconomical. A finite-element model (FEM) was developed and calibrated against the test results. A series of parametric analyses was carried out to investigate the effects of the screw spacing and shear stiffness on the elastic buckling load and ultimate load-bearing capacity. Finally, a practical design method was proposed to evaluate the column’s elastic buckling load and load-bearing capacity associated with flexural buckling. Compared with the simulation and test results, the proposed design method was accurate at predicting the load-bearing capacity of the specimens, with a relative difference of less than 6%.