# Seismic Behaviour of CFST Space Intersecting Nodes in an Oblique Mesh
## 10 Conclusions  
In this paper, the seismic performance of OMSIN under axial cyclic tension-compression loading was studied using ABAQUS.2022 finite element software. Six parameters were considered: space intersecting angle, symmetry coefficient, plane intersecting angle, out-of-plane restraint, steel content, and concrete strength. Furthermore, a dimensionless skeleton curve model of the OMSIN was established. Finally, a multi-parameter fitting correction was performed on the formula for the ultimate bearing capacity of CFST, and the theoretical calculation formulas for the yield load and ultimate load under axial compression were obtained under cyclic loading of the intersection nodes. The main conclusions are as follows:  
1. The ABAQUS three-dimensional solid model based on the core concrete constitutive model and the five-stage quadratic flow model used in this paper can effectively reflect the interaction between components of the OMSIN in seismic cyclic loading and can provide theoretical guidance for subsequent related research. 2. The increase in space angle significantly weakens effect on the seismic performance, and the space angle directly affects the failure mode of the nodes. Components with a space angle \(\geq\) 4\"are difficult to control regarding out-of-plane displacement, which can easily cause lateral instability failure. Moreover, large out-of-plane deformation has already occurred when the axial displacement is small. Therefore, it is not recommended to use such components in engineering practice due to economic and safety  
Figure 19: Comparison of theoretical calculation values and finite element model values. considerations. The asymmetric arrangement of the plane angle will cause the nonlinear development of out-of-plane displacement. When the symmetry coefficient is less than 0.70, the reduction in the ultimate bearing capacity of the nodes is significant. Larger out-of-plane and vertical deformation restraints should be applied for nodes with inconsistent upper and lower limb plane angles. 3. The specimens' ultimate load and overall compressive stiffness are positively correlated with the plane angle. Vertical restraints should be applied to the node positions of components with a plane angle \(\geq\) 70\({}^{\circ}\) to reduce vertical residual deformation. Out-of-plane restraint is a key factor affecting the seismic performance of the nodes, and it is proportional to the ultimate load of the components. However, when the ratio of the diameter of the steel rod to the outer diameter of the steel pipe used for out-of-plane constraints is \(\geq\)0.15, the change in out-of-plane constraints has no significant improvement effect on the seismic performance of the component. 4. The steel content is positively correlated with the components' positive and negative ultimate loads and overall stiffness. In structural design, if the aim is to improve the mechanical performance of the components by increasing the steel content, larger out-of-plane restraints should be set to utilize the material properties fully. The concrete strength is proportional to the positive ultimate load but has little effect on the negative ultimate load and hysteresis curve evolution. Components with higher concrete strength have a faster decay rate of axial compression stiffness due to their high brittleness in the later stages. When increasing the concrete strength, the hoop coefficient of the components should be increased simultaneously. 5. Three-line and two-line models were selected for the axial compression direction, and axial tension direction, respectively. A dimensionless skeleton curve model based on peak load and peak displacement of OMSIN was established. By fitting and modifying the formula for the ultimate bearing capacity of CFST, a formula for calculating the axial compressive yield load and ultimate load that can reflect the influence of all parameters is obtained.