## 2 Specim Design and Test Method  
### Specim Design  
Due to the limitation of bearing capacity provided by our shaking table facility, a quarter-scale spatial structural model of a single-span, two-story steel frame retrofitted by low-yield-point steel energy absorbers was designed in accordance with the Chinese Code for Seismic Design of Buildings (GB 50011-2010) [42]. The materials used for the test model were identical to those of the prototype structure, thereby indicating that the similitude ratio of the elastic modulus is \(S_{\text{E}}=1\). The scaling factor of the acceleration was thus taken as \(S_{\alpha}=2.5\) according to the maximum acceleration of ground records provided by the shaking table in laboratory conditions. The remaining similitude ratios of the mechanical parameters are listed in Table 1. The experimental results of the scaled model were then converted by the corresponding similitude ratios to obtain the dynamic responses of the prototype structure. The plane size of a specimen with a height of 0.8 m at each story, shown in Figure 1, was \(1.2\times 1.2\) m considering the limited size and loading capacity of the shaking table. Hot-rolled H-shaped steel with type specification of H \(100\times 100\times 6\times 8\) mm was adopted for all the frame columns (FC), and the I-shaped steel of I10 was used for all the main beams (MB) and secondary beams (SB). The LYP steel energy absorbers were connected to the lower flange of the main frame beam by equal-leg, double-angle steel bracing (EDB) with a type specification of \(2\L 45\times 3\) mm (Figure 1c). The low yield strength steel was then used for the four middle plates with a thickness of 8 mm welded to the two upper and lower ordinary steel plates with a 20 mm thickness in the metallic energy absorbers, whereas ordinary Q235B steel was applied in all other steel components. The additional mass blocks with a weight of 2 tons were mounted on each story of the specimen to simulate the weight distribution of the prototype structure accurately. Taking the mass blocks into consideration, the total weight of this specimen including the mass of the steel columns, beams, bracings, metallic energy absorbers, and connecting plates, was approximately 4.41 tons. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \begin{tabular}{c} **Physical** \\ **Quantities** \\ \end{tabular} & **Dimensions** & \begin{tabular}{c} **Similarity** \\ **Ratios** \\ \end{tabular} & \begin{tabular}{c} **Physical** \\ **Quantities** \\ \end{tabular} & **Dimensions** & \begin{tabular}{c} **Similarity** \\ **Ratios** \\ \end{tabular} \\ \hline \begin{tabular}{c} Length \\ Young’s modulus \\ Stress \\ Mass \\ Acceleration \\ \end{tabular} & \begin{tabular}{c} L \\ FL\({}^{-2}\) \\ \end{tabular} & \begin{tabular}{c} \(S_{\text{E}}=1\) \\ \(S_{\text{G}}=1\) \\ \(S_{\text{G}}=1\) \\ \(S_{\text{G}}=1\) \\ \(S_{\text{G}}=1/4\) \\ \(S_{\text{G}}=3.175\) \\ \(S_{\text{G}}=2.5\) \\ \end{tabular} & \
\begin{tabular}{c} Time \\ \(S_{\text{T}}=0.315\) \\ Poisson ratio \\ Stiffness \\ Frequency \\ Strain \\ \end{tabular} &
\begin{tabular}{c} T \\ \(S_{\text{V}}=1\) \\ \(S_{\text{K}}=1/4\) \\ \(S_{\text{H}}=3.175\) \\ \(S_{\text{G}}=1\) \\ \(S_{\text{G}}=1\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Similitudes of the test model. Figure 1: Specim size (unit: mm). (**a**) Plane layout; (**b**) elevation at first or second axis; (**c**) elevation at A or B axis. The bottom of the steel column in Figure 2 was strengthened by multiple stiffeners to achieve sufficient strength and stiffness, in order to prevent the column base from any premature formation of local buckling or plastic hinge during the tests.