Critical flexural buckling load for cold-formed steel built-up columns based on energy-variational principle

In the flexural deformation of the cold-formed steel (CFS) built-up section, the shear slip phenomenon will occur between the single sections, thus affecting the mechanical performance of the built-up section. In addition, accurately and efficiently calculating the critical elastic flexural buckling load of the of CFS built-up columns is an important basis for further exploring the mechanical properties of them. This paper selected five types of CFS built-up columns commonly used in engineering as research objects, analyzed the relative slip phenomenon of each single section during flexural deformation of the built-up section, and assumed the functional expression of the slip component based on the deformation differential equation. By considering the fastener arrangement and shear stiffness, the energy conservation equation was established, and the calculation method of the critical elastic flexural buckling load was derived based on the energy variation principle. In order to verify the accuracy of the calculation method, 112 numerical analysis models were developed based on ABAQUS, and the numerical results of the critical load were obtained using the buckling analysis. It is found that the simulation results are in good agreements with the results obtained using the proposed calculation method (with the relative errors less than ± 10%). The calculation method derived in this paper is applicable to the CFS built-up column, with self-tapping screw evenly arranged along the length of the column. The screw spacing should be between 100 mm and 600 mm, and the shear stiffness should not exceed 14 kN/ mm. The results of parameter analyses also indicate that the screw spacing and shear stiffness have a significant influence on the elastic critical load of the quadruple-limbs double-box section column, while only have a relatively small influence on the back-to-back open section and the face-to-face box section columns. © 2024 Science Press. All rights reserved.