## 3 Seismic Performance of RCS Composite Joints Under Floor Effect  
Based on the specifications, a floor slab is designed for node FJD-0 (Figure 10), with dimensions of 1315 mm \(\times\) 1040 mm and a thickness of 100 mm. The concrete strength is C25, and it contains double-layer HRB355 reinforcement with a diameter of 10 mm and a spacing of 100 mm, with a reinforcement ratio of 1.1 2%. The cover thickness is 20 mm. To coordinate the performance of the floor slab and steel beams, double-row shear studs are designed, using arc weld studs with a diameter of 16 mm and a height of 80 mm. According to Formula (12)-(14), 14 studs are required, and their spacing is reasonable. \[n_{f}=V_{s}/N_{v}^{c} \tag{12}\]  
\[N_{v}^{c}=0.43A_{s}\sqrt{E_{c}f_{c}}\leq 0.7A_{s}f_{u} \tag{13}\]  
\[V_{s}=min\left\{Af,b_{e}h_{c}f_{c}\right\}+A_{st}f_{st} \tag{14}\]  
where \(V_{s}\) is the longitudinal shear force in the cross section; \(N_{v}^{c}\) is the design value of the shear bearing capacity of the anchor bolt; \(E_{c}\) is the concrete's elastic modulus; \(b_{e}\) is the effective width of the steel beam; \(h_{c}\) is the floor thickness; \(f\) is the tensile strength of the steel beam; \(f_{c}\) is the design value of the concrete's compressive strength; \(f_{st}\) is the tensile strength of the steel bar; \(f_{u}\) is the design value of the ultimate tensile strength of the cylindrical head river; \(A_{s}\) is the section area of the anchor bolt; \(A\) is the section area of the steel beam. In the model, the contact between each component is simplified to ensure the convergence of calculation. The specific settings are as follows:  
* The concrete floor is bound to the column Tie;
* The reinforcing bars in the floor slab are combined into a reinforcing bar layer and embedded in the concrete area;  
Figure 9: **(a)** Comparison chart of experimental and simulated hysteresis curves; **(b)** Comparison of experimental and simulated skeleton curves; **(c)** Comparison of stiffness degradation curves. * The river contacts the tie binding the bottom of the floor slab with the upper flange of the steel beam. The finite element model of node FJD-0 is shown in Figure 11.  
Figure 11: FEM model of 3-node FJD-0. Figure 10: Design diagram of node FJD-0. In addition, the strength degradation calculation is given by Formula (15). \[\lambda_{j}=\frac{P_{j}}{P_{max}} \tag{15}\]  
where \(\lambda_{j}\) is the overall strength degradation coefficient; \(P_{j}\) is the peak load value of each level of cyclic loading; and \(P_{max}\) is the peak load value of the entire loading process. Node FJD-0 exhibits a uniform stress distribution under low cyclic loading, with a concentration of stress at the flange connection and the significant deformation of the steel beam bolt holes. The neutral axis shifts upward, leading to increased tensile stress. Failure is characterized by buckling and plastic hinges, consistent with the \"strong column, weak beam\" design principle. Concrete slab damage extends from the node to the distal end, with stress concentrated at the root of the connection (Figure 12). Figure 12: The damage pattern of node FJD-0. (**a**) Stress cloud map of node FJD-0; (**b**) Stress cloud map of node steel beam; (**c**) Stress cloud map of node connection bolts. By comparing the hysteresis curves, skeleton curves, stiffness degradation, and strength degradation of the prefabricated assembled RCS joint RCSJ3 without slab effects and the combined joint FJD-0 considering slab effects, it is evident that FJD-0 exhibits a higher peak load, stiffness, and ductility. Additionally, its energy dissipation capacity is enhanced, along with an overall increase in the stiffness of the combined joint, which improves its ability to resist strength degradation. This indicates that the presence of the slab significantly enhances the load-bearing capacity of the joint. For specific data, please refer to Figures 13 and 14.