## 5 Finite Element Analysis and Shear Capacity Checking Calculation
### Parameter Analysis and Shear Capacity Checking Calculation  
To investigate the impact of varying parameters on the seismic performance of joints, five new finite element models of assembled concrete with distinct axial compression ratios, post-cast concrete strength of joints, and steel tube diameters were developed. In these models, the strength grade of post-cast concrete is increased to C40, and the steel pipe specification is changed to an outer diameter of 60 mm and a wall thickness of 3.5 mm. These models are, respectively, designated as ZP-5.1, ZP-5.2, ZP-5.3, ZP-6, and ZP-7. Their specific parameters are articulated in Table 9.  
Analyses of the backbone curves in Figure 17 show that the backbone curves of ZP-5.1, ZP-5.2, ZP-5.3, and ZP-6 are fundamentally akin, each featuring an \"S\" shape. The initial stiffness offered from the numerical simulation results is noticeably higher than those yielded from the test results. Moreover, the overall bearing capacity observed in the ZP-5.1 joint is marginally superior to that from the ZP-1 simulation. Conversely, the ultimate load capacity from the ZP-5.2 joint is almost identical to the ZP-1 simulation, albeit with the former declining at a faster rate and demonstrating poor ductility. The initial stiffness and ultimate load capacity of the ZP-4 joint are in line with the simulated results of the ZP-1; however, the load-bearing potency of the ZP-4 joint experiences a significant decline after achieving peak load, which is considerably lower than the simulated results of ZP-1 and has limited ductility. After increasing the concrete strength of the ZP-6 joint to C40, the initial stiffness, ultimate load-bearing capacity, and ductility essentially match those of the ZP-1 simulation results. The results for ZP-7 show improved initial stiffness, overall load-bearing capacity, and ductility. The analysis suggests that, within a specific range, axial force is beneficial for shear resistance, aiding the advancement of initial stiffness and ultimate load-bearing capacity. However, when the axial force surpasses a certain limitation, it diminishes the joint's ductility. Enhancements to initial stiffness, ultimate load-bearing capacity, and ductility properties are achieved by augmenting the strength grade of the concrete in the joint's post-pouring region and incorporating steel piping into the column. As per the Chinese GB50010 Concrete Structures Design Code (hereinafter referred to as \"Concrete code\") [29], the shear capacity of reinforced concrete joints is determined by the joint core concrete and stirrups. Nevertheless, introducing an in-built steel pipe in the new type of joint significantly enhances the shear load-bearing capacity. Consequently, the calculation of the new connection's shear capacity is proposed as follows:  
\[V_{j}\leq\frac{1}{\gamma_{RE}}\left[1.1\eta_{j}f_{t}b_{j}h_{j}+0.05\eta_{j}N \frac{b_{j}}{b_{c}}+f_{y\
u}A_{s\
u j}\frac{h_{b0}-a_{s}^{\prime}}{s}+f_{\
u} A_{\
u}\right] \tag{10}\]  
where \(\gamma_{RE}\) is 0.85 when calculating the inclined sectional bearing capacity of frame joints; \(\eta_{j}\) is 1.50 for on-site cast floor slabs, but the recommended distribution, however, for a 9-degree fortification intensity is 1.25. For other conditions, the value is 1.00; \(A_{s\
u j}\) refers to the total cross-sectional area of each leg of the stirrup within the effective checking width range of the core area in the same cross-sectional direction; \(f_{y\
u}\) is the design value of tensile strength for transverse reinforcement; \(a_{s}^{\prime}\) is the distance between the resultant point of reinforcement in the longitudinal compression of the beam and the section's near edge; \(b_{j}\), \(h_{j}\) are the effective check width and height of the core area's cross-section for frame joints; \(h_{b0}\), \(b_{c}\) are the effective height and width for the beam section; and \(N\) is the design value of the axial force corresponding to the bottom of the upper column of the joint.