Static behavior of X-joints with SHS chord and CHS braces

Abstract

This paper investigates the behavior of X-joints with square hollow section (SHS) chord and circular hollow section (CHS) braces (XSCCB) under brace axial loading. A total of twenty-nine specimens were designed, including twenty-three empty specimens, three specimens filled with concrete only in the square chord and three specimens filled with concrete only in the circular braces. The effect of four influential factors was studied, including brace diameter to chord width ratio (β = d/b), chord width to double wall thickness ratio (γ = b/2 T), brace wall thickness to chord wall thickness ratio (τ = t/T) and partial concrete filling on the behavior of XSCCB under brace axial loading. Initial stiffness and ultimate bearing capacity of empty XSCCB increase as the β increases and the γ decreases. The ductility coefficient of empty XSCCB increases as β increases, while γ has little effect on their ductility coefficient. Also, τ has a minor effect on the ultimate bearing capacity, initial stiffness and ductility coefficient of empty XSCCB. However, for XSCCB filled with concrete only in the chord member, the initial stiffness, ultimate bearing capacity and ductility coefficient increase as τ increases. For the XSCCB filled with concrete only in the braces, τ has little effect on the ultimate bearing capacity, initial stiffness and ductility coefficient. Chinese Code and Eurocode 3 are generally conservative for designing empty XSCCB under brace axial loading. Hence, the corresponding formulas are proposed for calculating the ultimate bearing capacity of empty XSCCB under brace axial loading.