Comparison of in-plane flexural seismic behavior between traditional RHS X-joints and eccentric RHS X-joints

A test investigation is performed on the seismic behavior of the novel eccentric and traditional rectangular hollow section (RHS) X-joints subjected to in-plane bending moment (IPBM). Four specimens, including two tradition joints and two eccentric joints with different brace/chord width ratio (beta),under quasi-static cyclic IPBM are tested. Test results exhibit that the two specimens with large beta(beta = 1.0)are failed due to weld tearing, while the two specimens with medium beta(beta = 0.83) are failed by the tearing of both weld and the chord face. Furthermore, the connecting web tearing also occurred in the two eccentric joint specimens. For both traditional and eccentric X-joints, increasing beta can significantly improve flexural strength, but reduce ductility ratio, deformability and energy dissipation characteristics. Seismic behavior of the X-joints also affected by the braceto-chord connection patterns. In particular, the eccentric X-joint (eccentric brace-to-chord connection) with medium beta exhibit larger strength, similar energy dissipation characteristics but smaller ductility ratio than those of the counterpart traditional X-joint (centric brace-to-chord connection); while the eccentric X-joint with large beta exhibit similar strength but better energy dissipation characteristics and higher ductility ratio than those of the counterpart traditional X-joint. The results also demonstrates that the code equations make conservative predictions on the strength of the traditional X-joints. Finally, the reasons behind the experimental observation is further explained by FE analysis and the load transferring analytical models proposed in this study.