Hysteretic behavior of CHS X-joints under in-plane bending moment

In this paper, hysteretic behavior of circular hollow section (CHS) X-joints under in-plane bending moment (IPBM) is investigated. Firstly, carried out experimental study on three CHS X-joints with different brace-to-chord diameter ratio (beta) and brace-to-chord angle (theta) under cyclic IPBM. Test results show that three specimens eventually failed by tearing of the chord wall in the brace/chord connection region. Before cracking, the chord wall in the connection region experienced large plastic deformation which provide significant energy dissipation; and the resistance decreases slowly after cracking due to ductile crack propagation. Test results also indicate that flexural hysteretic of the X-joints is greatly affected by the two parameters (beta and theta). Specifically, either increasing beta (from 0.73 to 0.89) or deceasing theta (from 90 degrees to 70 degrees) is benefit to ductility ratio, flexural strength and energy dissipation behavior. The test observation is further explained and confirmed by a model of load transfer mechanism (a semi-cylindrical shell constrained by the directional supports) and the finite element (FE) pa-rameters analysis with extended range of the above two parameters. Then, a hysteretic model is proposed to simulate in-plane flexural hysteretic behavior of the CHS X-joints, and the hysteric model is verified by test and FE results. Finally, effect of chord moment and brace axial force on the in-plane flexural behavior of the X-joints was investigated by FE analysis.