Fire resistance of box-shape cold-formed steel built-up columns failing in global buckling: Test, simulation and design

Abstract

Box-shape cold-formed steel built-up columns (CFS-QBC) are popular in multi-story CFS buildings. This paper conducted experimental research, numerical simulation, and parametric analyses to investigate its fire resistance. Twelve slender columns failing in global buckling were tested in a transient fire condition, where different initial load ratios and screw spacing were considered. The results showed that the specimen’s critical temperature decreased with the screw spacing, and the screw spacing could significantly affect the deformation modes; Besides, the end fastening group (EFG) had little effect on the fire resistance. When the screw spacing was less than 300 mm, the effectiveness of the composite action of the built-up section at elevated temperatures was demonstrated by the consistency of the deformation compatibility among the components of the built-up section. Numerical simulations were then performed, including heat transfer and structural analysis, calibrated and verified against the tests. Based on the numerical model, the load ratio and screw spacing were parametrically analyzed to study their effects on the fire resistance of the columns. Finally, a simplified design method was proposed to evaluate the load-bearing capacity of CFS-QBC at elevated temperatures.