Elastic buckling of composite webs in back-to-back cold-formed steel built-up columns-Part II: Design formula

Abstract

Elastic buckling of the composite webs in cold-formed steel (CFS) back-to-back built-up columns was investigated in this paper. The built-up members were fabricated from two identical C-section components and were assembled with self-drilling screws on their webs. The new buckling modes of screw composite plates with simply supported on four sides (SS) have been determined by previous experiments and numerical simulations. In this paper, the instability mechanism was analyzed based on the small deflection theory to study the elastic buckling behavior of SS screw composite plates. Immediately, a calculation model of SS screw composite plates was established considering the shear slip and the screw restraint. The analytic formula of elastic critical stresses was deduced based on the calculation model. However, the critical stress is affected by the ratio of the web length to the depth of the web, the screw diameter and the screw spacing. The proposed formula was modified using previous results obtained by extensive finite element parametric analyzes to increase the applicability for the proposed analytical formula in SS screw composite plates. Eventually, the applicability and accuracy of the design formula were validated using the previous experimental results. Therefore, a new stability calculation theory and a design formula considering the influence of shear slip were proposed to solve the defects in solving the buckling problem of screw composite plates using the classical stability theory of the single plate.