Based on ADINA program, numerical analysis was applied to study the hysteretic behavior of K-type welded outer sleeve RHS joints subjected to axially cyclic load, using the nonlinear method of Newton-Raphson with Low-Speed Dynamics Damping Factor. Considering the influencing factors such as elastic-plastic material, large deformation, and tearing failure, the skeleton curve and ductility coefficient were obtained, which were the main indexes reflecting RHS joints seismic behaviors. By changing the geometrical parameters of the outer sleeve joints(the length and thickness of the outer sleeves, the branch pipes to main pipes width ratio), the variation regularity of the joints hysteretic behaviors was studied and the restoring force model was proposed. The analysis showed that the hysteretic behavior of K-type welded outer sleeve RHS joints is much better than that of the non-strengthen joints, and it can improve the ultimate capacity by raising the thickness ratio between the outer sleeve and the chord.
