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

Abstract

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 (β) and brace-to-chord angle (θ) 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 (β and θ). Specifically, either increasing β (from 0.73 to 0.89) or deceasing θ (from 90° to 70°) 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) parameters 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.