Axial compression capacity of steel CHS X-joints strengthened with external stiffeners

The axial compression capacity of X-joints with and without external stiffeners was experimentally and numerically investigated. Two reinforced X-joints, with the brace-to-chord diameter ratio (β) equal to 0.51 and 0.73, were tested in this study and compared with the unreinforced ones from previous work. The failure modes and load-displacement curves of the unreinforced and reinforced X-joints were compared. The comparison showed that within the range of geometric studied, the external stiffener could increase the ultimate strength of the X-joints without reinforcement. The results of the finite element simulations on the X-joints with and without external stiffeners were verified against the experimental data. 256 X-joint FE models were generated and analysed to investigate the failure modes, the influence of the size of external stiffeners and joint geometry on the improvement of ultimate capacity of the joints under axial compression. Finally, a theoretic formulation, based on the modified yield line model, was developed and examined by the experimental and numerical results.