# Seismic Behaviour of CFST Space Intersecting Nodes in an Oblique Mesh
## 3 Finite Element Model
### Reliability Verification of Finite Element Model  
The plane and space intersection angles of the components used for verification are \(35^{\circ}\) and \(1^{\circ}\), respectively, and the thickness of the connecting plate is \(17\) mm. The strength grade of the node concrete is C90, and that of the non-node area concrete is C70. Figure 3 shows the comparison between the load-displacement curves of the experiment and the finite element model. As shown in Figure 3a, the evolution of the load-displacement curves of the two is basically consistent before the peak load. Both curves show linear growth before the displacement reaches \(8\) mm, indicating that the components are in the elastic stage. After the displacement exceeds \(8\) mm, the slope of the curve decreases slightly until \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Steel Type** & **Model Number** & \begin{tabular}{c} **Elastic Modulus** \\ _E\({}_{s}\)/MPa** \\ \end{tabular} & \
\begin{tabular}{c} **Yield Strength** \\ _f\({}_{\mathrm{y}}\)/MPa** \\ \end{tabular} &
\begin{tabular}{c} **Ultimate Strength** \\ _f\({}_{\mathrm{u}}\)/MPa** \\ \end{tabular} \\ \hline Outer steel pipe & Q345B & \(2.06\times 10^{5}\) & \(380\) & \(574\) \\ Elliptic & Q345B & \(2.06\times 10^{5}\) & \(365\) & \(570\) \\ \(\phi\)42 steel bar & \(40\)Cr & \(2.06\times 10^{5}\) & \(785\) & \(930\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mechanical Properties of Steel. the peak. However, the experimental curve stops loading immediately after reaching the peak load, so there is no downward section consistent with the finite element curve. The elastic stiffness and peak load of the finite element component are slightly higher than those of the experimental component. This is because, in actual situations, the concrete contains a certain amount of porosity, which causes differences between the concrete in the actual situation and the homogeneous solid in the finite element model. In addition, the peak load corresponding to the experimental curve is slightly larger than that of the finite element model since the concrete in the actual situation is a porous and non-uniform material and a more significant displacement is required to close the initial gap. According to Figure 3b, the finite element curve shows linear growth in out-of-plane displacement, while the experimental curve shows a sudden change in slope at an axial displacement of 7 mm. This is because the axial compression loading of the steel tube in the experiment cannot be guaranteed to be absolutely along the axis of the steel tube; i.e., there is a certain eccentricity, which causes the slow development of lateral displacement in the early stage and a sudden increase in lateral displacement in the later stage. However, overall, the maximum difference between the out-of-plane displacement of the experiment and the finite element is only 1.27%, which is in good agreement. As shown in Figure 3c, the strain-load curves of the two measuring points have similar evolution patterns. Due to the ideal nature of the model in the finite element analysis, the slope of the finite element curve is more significant than that of the experimental curve. However, the peak strains at points C and D differ by 8.49% and 2.00%, respectively. Overall, the finite element model and the experimental results show good agreement. Figure 4 shows a comparison between the Mises stress cloud map of the finite element model and the experimental situation. As shown in Figure 4a-d, both the experimental and finite element components experience two types of failure: buckling failure of the steel tube in the node area and bending failure of the steel tube in the non-node area. According to Figure 4c, when the wall thickness and concrete strength of the steel tube in the node area and non-node area are inconsistent, the Mises stress shows non-uniformity along the boundary line, indicating that changes in wall thickness are not conducive to the uniform transmission of stress.