# Seismic Behaviour of CFST Space Intersecting Nodes in an Oblique Mesh
## 6 Discussion
### Out-of-Plane Constraints  
Figure 13 shows the parameter curves of specimens with different out-of-plane constraints. As shown in Figure 13a-c, the size of the out-of-plane constraint was proportional to the ultimate load of the component. The specimens with \(\dot{\omega}\) values of 0.15 and 0.20 exhibited stronger load-carrying capacity during the axial compression cycle, and the descending segment of the curve after the peak was not apparent. The positive and negative skeleton curves tended to coincide, and the energy dissipation capacity was similar. This indicates that 0.15 was the limit point at which changes in out-of-plane constraints can improve the seismic performance of nodes. According to Figure 13c, the overall stiffness of the components with \(\dot{\omega}\) of 0.15 and 0.20 was the largest, while that of the component with \(\dot{\omega}\) of 0 was the smallest. The negative stiffness degradation curves of the components with \(\dot{\omega}\) of 0 and 0.05 tended to coincide, indicating that changing \(\dot{\omega}\) had no significant improvement on the node's tensile stiffness degradation rate within the range of \(\dot{\omega}\leq 0.05\). When \(\dot{\omega}\geq 0.15\), changing the size of the out-of-plane constraint had no significant improvement on the seismic performance of the component.  
According to Figure 13d, the node with \(\dot{\omega}\) of 0, i.e., without lateral constraint, exhibited nonlinear growth of vertical and out-of-plane displacement in the later stage of the cycle, with peak values of \(-16.15\) mm and \(102.90\) mm, respectively. This was also the main reason for its sudden increase in energy dissipation capacity (Figure 13e). The specimens with \(\dot{\omega}\) of 0.05 and 0.10 exhibited a significant descending segment in the positive direction of the hysteresis curve, and the latter exhibited a sudden drop-unloading phenomenon of the skeleton curve after the axial displacement was 10 mm, mainly due to the fracture of the lateral constraint bar in the 0\({}^{\circ}\) direction. The skeleton curve then stabilized and had an upward trend, mainly due to the lateral constraint in the \(\pm 45^{\circ}\) direction beginning to constrain the out-of-plane deformation. Except for the unconstrained nodes that experienced large out-of-plane deformation failure, the energy dissipation capacity of the other specimens increased with the increase in \(\dot{\omega}\), indicating that the out-of-plane constraint is a key factor affecting the seismic performance of the node.  
Figure 14 shows the Mises stress cloud maps of components with different out-of-plane constraint sizes. As shown in the figure, the two failure modes were large out-of-plane deformation failure and bending failure of the steel tube in the non-node area, respectively. The area of the maximum Mises stress of the component with \(\dot{\omega}=0\) occurred on the concave side of the connecting plate, and the area of the extreme value was relatively large. The stress extreme value area of the component with \(\dot{\omega}=0.20\) was in the steel tube of the non-node area, indicating that the out-of-plane constraint affects the failure mode and location of the component.  
Figure 12: Mises stress nephogram and compression damage nephogram of members with different steel content. (**a**) \(\varphi=0.05\). (**b**) \(\varphi=0.05\). (**c**) \(\varphi=0.20\). (**d**) \(\varphi=0.25\).