## 3 Seismic Shaking Table Tests
### Description of Seismically Isolated Test Mockup  
As shown in Table 1, the designed LRB has a vertical load of 10 kN (\(\cong\) 1 ton) to perform the seismic isolation frequency of 2.3 Hz. To validate their seismic isolation characteristics  
\begin{table}
\begin{tabular}{c c} \hline
**Design Parameters** & **Design Value** \\ \hline Outer Diameter (\(D_{\mathrm{o}}\)) & 100 mm \\ Lead Plug Diameter (\(d\)) & 21.5 mm \\ Total Rubber Height (\(t_{\mathrm{R}}\)) & 20 mm \\ Total LRB Height (\(t\)) & 34 mm \\ Shape Factor (\(S_{1}\)) & 9.9 \\ Shape Factor (\(S_{2}\)) & 5.0 \\ Design Vertical Load (\(P_{\mathrm{d}}\)) & 10 kN \\ Design Shear Displacement (\(D_{\mathrm{d}}\)) & 35 mm (175\%) \\ Beyond Design Shear Displacement (\(D_{\mathrm{b}}\)) & 80 mm (400\%) \\ \hline \end{tabular}
\end{table}
Table 1: Summary of LRB design parameters [21].  
\begin{table}
\begin{tabular}{c c c} \hline
**Parameters** & **Design** & **Quasi-Static Tests** \\ \hline Horizontal Isolation & & \\ Frequency (\(F_{\mathrm{iso}}\)) & 2.3 Hz & 2.25 Hz \\ Equivalent Horizontal & & \\ Stiffness (\(K_{\mathrm{eff}}\)) & 209 kN/m & 199.3 kN/m \\ Critical Damping Ratio (\(\xi\)) & 25.4\% & 24.1\% \\ Tangential Stiffness (\(K_{\mathrm{i}}\)) & 123 kN/m & 122 kN/m \\ Characteristic Strength (\(Q_{\mathrm{d}}\)) & 3 kN & 2.72 kN \\ \hline \end{tabular}
\end{table}
Table 2: LRB dynamic characteristics at design level [21].  
\begin{table}
\begin{tabular}{c c} \hline
**Item** & **Performance** \\ \hline Max. Loading (kN) & 300 \\ Table Size (m) & 4 \(\times\) 4 \\ Control Axes & 6 DOF (Translation 3 axes, Rotational 3 Axes) \\ Max. Displacement (mm) & Hor. (X, Y) = \(\pm\)300, Ver. (Z) = \(\pm\)150 \\ Max. Velocity (m/s) & Hor. (X, Y) = 1.5, Ver.(Z) = 1.0 \\ Max. Acceleration (g) & Hor. (X, Y) = 3.0, Ver.(Z) = 5.0 \\ Frequency Range (Hz) & 0.1 \(\sim\) 60 \\ Excitation Mechanism & Electro-hydraulic Servo, 3 Variable Control Software & MTS 469D \\ Feedback Data Acquisition & 63 Channels (Sampling Rate = 512 Hz) \\ \hline \end{tabular}
\end{table}
Table 3: Shaking table performance.  
during the actual seismic loading conditions, the total dummy mass of 4 tons is fabricated with a rectangular shape (1300 mm \(\times\) 1300 mm \(\times\) 320 mm) and four LRBs are installed between the shaking table and the bottom of the dummy mass at each corner with bolted joint connection, as shown in Figure 1.  
To investigate the seismic isolation performance induced by LRBs, three beam structures (S1-S3) are installed both on the shaking table and on the dummy mass, which will represent the actual superstructures to be seismically isolated. The target natural frequencies for beam structures are 5 Hz for S1, 9 Hz for S2, and 20 Hz for S3. When considering the design seismic isolation frequency of 2.3 Hz, the S1 structure is set to investigate the seismic responses of the structure near the seismic isolation frequency. The S2 structure is aimed to investigate the seismic isolation performance for the strong input motion having a spectral peak around 10 Hz. The S3 structure is prepared to validate the seismic isolation responses of superstructures having high-frequency dynamic characteristics.  
For the measurement of seismic responses, the accelerometers are installed on the shaking table for the input seismic motion and on the center of the dummy mass for the seismic isolation response. To obtain the seismic responses of the beam structures both on the shaking table and on the dummy mass, the accelerometers are attached at top of each beam structure. To measure the LRB shear displacement response, which will be the relative displacement between the shaking table and the dummy mass, the LVDT (Linear Variable Differential Transformer) is installed between the sensor supports (Figure 1) and the dummy mass.