## 3 Test Design
### Model Structure  
To model the reinforcement concrete (RC) structure of a station in proper detail, fine granular concrete was adopted as the material to produce the model structure. The concrete was a mixture of cement, sand, lime and water, with a ratio of 1:5.8:0.6:0.6 by mass. As shown in Table 3, the compressive strength and density of the concrete were 10.6 MPa and 1.86 kg/m\({}^{3}\), respectively. Galvanized steel wires were utilized for longitudinal and transverse reinforcement. Table 4 summarizes the dimensions and compressive strength of the steel wires. The reinforcement ratios were determined by considering the resistance of the bending moment of the prototype structure, scaled down and employing the previously deduced similitude relations.  
As discussed previously, two model structures were constructed in the experiments, including a model of an interchange station and a model of a single station. As depicted in Figure 4a, the cross station model contained a two-story structure and a three-story structure, both with a total length of 4.6 m. The width of the square conjunction was 920 mm, denoted as \(W\). Each side of the two-story station out of the conjunction was 2\(W\) in length, which means only part (116 m) of the prototype interchange station (155 m) was physically modeled. This discrepancy was mainly due to the limitations on the geometry and capacity of the shaking table. However, the discrepancy was considered to be acceptable, since a preliminary numerical study on the seismic response of the prototype station showed that the length of the most-affected region of the conjunction was within two times the cross-section width [28]. A two-story single-station model, which had the same cross-section as the two-story section of the cross station, was constructed as a reference. The final model structures are shown in Figure 4. The dimensions of the cross-sections of the two-story and three-story structures are illustrated in Figure 5, in which the former one is identical in both the single station and the interchange station. The relative stiffness of the station structure corresponding to the surrounding soil was a major factor for the seismic response. According to [PERSON] [8], the similitude ratio \(S_{F}\), in terms of flexibility, can be derived as follows:  
\[S_{F}=\frac{G_{m}W_{m}S_{p}H_{p}}{S_{m}H_{m}G_{p}W_{p}} \tag{2}\]  
where the subscripts \(p\) and \(m\) represent the prototype and the model, respectively, \(G\) is the shear modulus of the soil and \(W\), \(H\) and \(S\) are the width, height and unit stiffness of the structure, respectively. Focusing on the two-story single-station structure, \(S_{F}\) was calculated by 2D FE analysis, obtaining a flexibility similitude ratio \(S_{F}=1\):1.4 according to Equation (2). This implies that the relative stiffness of the model structure was 1.4 times greater than that of the prototype.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Item** & **Diameter \(\Phi\) (mm)** & **Density \(\rho\) (kg/m\({}^{3}\))** & **Strength \(f_{0}\)** & **Elastic Modulus \(E\) (GPa)** \\ \hline Steel wire 22 & 0.7 & 7850 & 312 & 205 \\ Steel wire 18 & 1.2 & 7850 & 347 & 205 \\ Fine granular concrete & - & 1860 & 10.6 & 9.6 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Properties and key dimensions of materials used to construct the model structure.