## 3 Base Model Design  
A single-story, single-span, high-strength eccentrically braced steel frame structure with a variable-section replaceable link was selected from the prototype structure for finite element simulation, with a frame beam length of 2480 mm, a frame column height of  
Figure 11: Comparison of failure modes. Figure 12: Comparison of hysteretic curves. Figure 13: Comparison of backbone curves. 3600 mm, and a replaceable link length of 1840 mm. The deformations of the replaceable link, connection plate, and bolts were accurately modeled. The FEM models were created using the tension function in ABAQUS software. The cross-section dimensions and lengths of the components are shown in Table 2. The member sections were built-up sections, and H-sections were used for the members, where \"H\" refers to the welded H-shaped section, and the following numbers are section depth \(h\), flange width \(b_{\text{f}}\), web thickness \(t_{\text{w}}\), and flange thickness \(t_{\text{f}}\). A diagram of the replaceable link is shown in Figure 14. The length ratio \(\rho\) is determined by the plastic shear capacity \(V_{\text{p}}\) and the plastic bending capacity \(M_{\text{p}}\) of the link, which is calculated by Equations (1)-(3). \[V_{p}=0.58f_{\text{y}}A_{\text{w}} \tag{1}\]  
\[M_{p}=f_{\text{y}}W_{\text{y}} \tag{2}\]  
\[\rho=e/\left(\frac{M_{p}}{V_{p}}\right) \tag{3}\]  
where \(f_{\text{y}}\) is the yield strength of the replaceable link; \(A_{\text{w}}\) is the cross-sectional area of the web in the link; \(W_{\text{y}}\) is the plastic modulus of the full section in the link; \(e\) is the length of the energy dissipation region. The length ratio of the replaceable link is calculated according to the length of the energy-consuming region \(e\). The length ratio \(\rho\) = 1.17 \(<\) 1.6 calculated according to Equations (1)-(3) indicates that the designed replaceable link of the variable section is of shear yielding type. From the section size and section form of the link, the end moments \begin{table}
\begin{tabular}{c c c} \hline \hline
**Specimen** & **Cross-Section** & **Length/(mm)** & **H-Shaped Section** \\ \hline Beam & H620 \(\times\) 180 \(\times\) 10 \(\times\) 16 & 2480 \\ Column & H400 \(\times\) 400 \(\times\) 12 \(\times\) 12 & 3600 \\ Brace & H260 \(\times\) 180 \(\times\) 10 \(\times\) 16 & 4275 \\ Energy consuming region & H500 \(\times\) 180 \(\times\) 10 \(\times\) 16 & 840 (\(e\)) \\ link & H620 \(\times\) 180 \(\times\) 10 \(\times\) 16 & 1840 (\(e^{\prime}\)) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Dimensions of elements. Figure 14: Section size of the link. and shear forces of the link are calculated according to Equations (4) and (5) when the ultimate bearing capacity is reached. \[V_{u}=\varphi V_{p} \tag{4}\]  
\[M_{u}=\frac{\eta(eV_{p})}{2} \tag{5}\]  
where \(\varphi\) is the shear capacity strengthening factor for the link after consideration of the material over strengthening and strain hardening, usually \(\varphi=1.5\); \(\eta\) is the seismic action adjustment factor, determined according to the seismic intensity of the frame. When designing the bolted connection of the variable-section replaceable link to the frame beam, it is assumed that the end moments are all carried by the upper and lower flange bolts and \(V_{\text{uf}}\) is the shear force at the flange caused by the end moments \(V_{\text{uf}}=M_{\text{u}}/h\). The web splice bolts only carry the end shear force; see Figure 15 for a schematic calculation. The finite element model (FEM) was established using ABAQUS software, and the C3D8R solid element was selected for the model. In the FEM model, the parts were bonded together using a tie restraint, and the residual deformation and stress concentration of the steel plate caused by the high welding temperature were ignored. In mesh generation, hexahedral elements are used to improve the calculation accuracy, and the mesh is refined appropriately in the link area. The bolt pretension force is considered in multiple steps to converge the calculation.