Theoretical and experimental investigations on the stability performance of concrete-filled steel tubular X-column with regard to the flexural rigidity variation

The concrete-filled steel tube (CFST) X-column comprises two intersecting steel tubes filled with concrete, having irregular cross-sections that vary along its length, leading to variation in its flexural rigidity. This poses a challenge in terms of its buckling instability, a vital consideration in engineering practices. Hence, this study aims to investigate the stability performance of slender CFST X-columns. Firstly, the flexural rigidity of the two common types of CFST X-columns (through-type and reinforced-type) was calculated, and utilizing the stationary potential energy principle the elastic buckling loads of the both types of CFST X-columns were determined. The results indicated that the elastic buckling loads primarily depend on the position and length of the cross area. Next, the stability factors for both cases were calculated, and a formula for determining the stability bearing capacity of the CFST X-column was proposed. Finally, an experimental investigation of the stability behavior of CFST X-columns was conducted to validate these theoretical findings. The test specimens underwent a comprehensive analysis of their load-carrying process, and the instability failure mode as well as the deformation development were obtained. The experimental results demonstrated that within the given range of slenderness ratio, the specimens experienced elastic-plastic instability under axial compression. The calculated stability bearing capacity derived from the theoretical analysis closely matched the experimental results, indicating the reliability of the proposed theoretical analysis method. This provides valuable reference for the practical application of this novel component in engineering projects.