Effect of the brace-to-chord angle on the out-of-plane flexural behavior of unstiffened CHS X-joints

Unstiffened circular hollow section (CHS) tubular X-joints, which are widely applied to single-layer reticulated shell structures, usually have the geometric characteristics of non-orthogonal in-plane angle (IPA) and non-zero out- of-plane angle (OPA) between brace and chord. To investigate the effect of the IPA and OPA on the out-of-plane flexural behavior of the X-joints, an experiment on two unstiffened CHS X-joints with different IPA under cyclic out-of-plane bending moment (OPBM) were performed, and theoretical analysis and finite element (FE) analysis were also conducted. It indicated that two joints behave excellently in deformability and seismic resistance, and the energy dissipated of the X-joints mainly rely on plastic deformation and crack propagation of the chord wall. The results also shown that the X-joints with smaller IPA have higher flexural capacity and better seismic behavior than X-joints with larger IPA, because more uniform plastic development and slower growth strain at the chord wall near to intersection for the former joints. OPA reduces the flexural elastic stiffness and the flexural capacity of the X-joints under reverse OPBM. However, OPA is conducive to strengthening the flexural capacity of the X-joints under positive OPBM.