Strength of external-ring-stiffened tubular X-joints subjected to brace axial compressive loading

This paper presents the results of numerical and analytical studies to obtain ultimate strength enhancement coefficient (Re) equations for external-ring-stiffened circular hollow section (CHS) X-joints under axial compression. The FE modeling approach is validated by the results of axial compressive experiments conducted in the authors' previous research on six X-joints with and without stiffeners. In all, 160 unstiffened and ring-stiffened FE models of CHS X-joints subjected to brace axial compression were investigated. The effects of the brace-to-chord diameter ratio β, the ratio of chord diameter to twice the chord wall thickness γ, the stiffening ring width factor βr (i.e. 2br/d0 where br is the ring width and d0 is the chord diameter), and the stiffening ring thickness factor τr (i.e. tr/t0 where tr is the stiffening ring thickness and t0 is the chord wall thickness) on the structural behavior of external-ring-stiffened CHS X-joints were evaluated. Parametric analysis showed that the ultimate strength enhancement coefficient Re decreased with the increase in the diameter ratio between the brace and the chord β, but once β exceeded 0.4, the effect on Re was slight. Furthermore, the ratios of chord diameter to twice the chord wall thickness γ, the stiffening ring width factor βr, and the stiffening ring thickness factor τr were all positively correlated with improvement in the ultimate strength of the external-ring-stiffened CHS X-joints. An analytical formula based on the yield volume model was derived to predict the ultimate strength enhancement of external-ring-stiffened X-joints.