## 2 Finite Element Model of Prefabricated Modular RCS Composite Node
### Finite Element Analysis and Verification of Prefabricated RCS Composite joints
These reference points are connected to the loading surfaces, allowing for the application of constraints and loads at each of the three points. Additionally, to avoid instability and torsional effects at the beam end during loading, constraints are imposed on  
Figure 6: Grid division. (**a**) Grid encryption area; (**b**) Overall grid. the y-direction displacement as well as the rotation angles in the x and z directions at the beam end loading point via the coupling point RP-3 (U2 = 0, UR1 = 0, UR3 = 0). To verify the effectiveness of the finite element model, the simulation results were compared with experimental data. The failure mode at the nodes showed that the maximum stress at the high-strength bolt was 990 MPa and that the maximum stress in the steel beam and core plate was 420 MPa, which is consistent with the experimental observations. Although there are minor differences, it is preliminarily assumed that these differences are due to initial defects and slip phenomena in the specimens, indicating that the finite element model has reference value (Figure 8). In reference [29], the study on reinforced T-shaped CFST column-steel beam joints verified the model's reliability through comparisons between finite element simulations and experimental data. In addition, based on the stress distribution of the simulated nodes, the stress values in the steel beams are uniformly distributed between 155 MPa and 285 MPa. The average errors in initial stiffness and ultimate load capacity met the required standards, similar to the validation presented in this paper, further confirming the effectiveness and accuracy of the finite element model in joint studies. The hysteretic curve reflects the behavior of the structure under repeated loading, with the simulation results consistent with the experimental trends, demonstrating excellent seismic performance. The finite element model did not exhibit significant shrinkage, due to the loosening between components in the experiment. The skeleton curves evaluate the mechanical properties of components at different load stages, and both the simulation and experimental skeleton curves are effective. As loading increases, stiffness degradation becomes more pronounced, but the two curves remain consistent (Figure 9). The analysis of stiffness degradation generally reflects the degradation of node stiffness by examining the variation in the loop stiffness under the condition of uniform displacement, as expressed by the following Formula (11). \[K_{j}=\frac{\sum_{i=1}^{n}P_{j}^{i}}{\sum_{i=1}^{n}\Delta_{j}^{i}} \tag{11}\]  
where \(K_{j}\) is the loop stiffness under the j-th level of loading, measured in Kn/m;  
Figure 7: Boundary condition settings. \(p_{j}^{i}\) is the maximum load during the i-th cycle under the j-th level of loading; \(\Delta_{j}^{i}\) is the maximum displacement during the i-th cycle under the j-th level of loading; \(n\) is the number of loading cycles. Figure 8: Comparison of test and simulation node damage morphology. Through the above comparison and analysis, it appears that the flanges of steel beams and the pressure-bearing steel plates are buckled when the nodes are destroyed, and the bolt holes gradually expand. The plastic hinges and the location of damage are consistent with the test results. The method of verifying the finite element model in this study is similar to that in the literature [30], where the C3D8R element was used to simulate concrete and steel beams, and the model reliability was verified through the comparison of hysteretic curves and skeleton curves. The results indicate that the difference in the bearing capacity between the simulations and experiments is less than 9%, and that the pattern in the degradation of node stiffness is consistent. These findings support the effectiveness and reliability of the finite element model, laying a foundation for our subsequent seismic performance analysis.