# Seismic Response of a Large LNG Storage Tank Based on a Shaking Table Test
## 2 Shaking Table Test of Storage Tank Models
### Analysis of Test Results
#### 2.3.2 Isolated Storage Tank  
In order to compare the effect of the isolation bearing, the acceleration responses of the non-isolated storage tank and the isolation storage tank are compared, as shown in Figure 5. Under the same seismic wave excitation, for the non-isolated storage tank, the acceleration response roughly shows a linear increasing trend, while for the isolated storage tank, the acceleration response first decreases with the increase in height, and when it reaches the middle of the tank wall, the acceleration response decreases. The acceleration response in turn increases with altitude. This is mainly due to the introduction of a soft horizontal layer (i.e., seismic isolation bearing) at the bottom of the storage tank, the energy dissipation of seismic waves through the horizontal layer, and the energy transmitted to the upper structure of the storage tank is attenuated.  
The acceleration response of the concrete outer tank and the steel inner tank is significantly reduced after the isolation bearing is adopted. In different test directions, the vibration isolation bearings can reduce the acceleration response of the storage tank, and the reduction is more obvious in the loading direction. With the increase in the height of the acceleration measuring point, the seismic isolation effect is more obvious.  
The displacement of the tank becomes larger due to the introduction of a soft horizontal layer at the bottom of the tank. From three different loading modes (X direction, XZ direction, XYZ direction), different peak accelerations and different seismic waveforms, the maximum displacement responses of the dome top of the isolated storage tank and the non-isolated storage tank were compared. The calculation formula of the amplification factor is:  
\[amplification\ factor=(u_{iso}-u_{non-iso})/u_{non-iso} \tag{1}\]  
where \(u_{iso}\) is the displacement of the isolation tank and \(u_{non-iso}\) is the displacement of the non-isolation tank.  
It can be seen from Table 4 that after the isolation bearing is used, the displacement of the storage tank will be amplified to a certain extent.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Loading Case**} & \multicolumn{2}{c}{**Isolated Storage Tank**} & \multicolumn{2}{c}{**Non-Isolated Storage Tank**} & \multicolumn{2}{c}{**Amplification Factor**} \\ \cline{2-7}  & **X** & **Y** & **X** & **Y** & **X** & **Y** \\ \hline Wolong wave (X direction, 0.5 g) & 4.04 & 0.18 & 3.90 & 0.17 & 3.59\% & 5.88\% \\ Wolong wave (XZ direction, 0.5 g) & 4.14 & 0.14 & 3.77 & 0.13 & 9.81\% & 7.69\% \\ Wolong wave (XYZ direction, 0.5 g) & 3.97 & 3.95 & 3.77 & 3.70 & 5.31\% & 6.76\% \\ Wolong wave (XZ direction, 0.75 g) & 5.89 & 0.18 & 5.55 & 0.17 & 6.13\% & 5.88\% \\ Wolong wave (XYZ direction, 0.75 g) & 7.88 & 7.27 & 7.37 & 7.14 & 6.92\% & 1.82\% \\ Artificial wave (XYZ direction, 0.25 g) & 9.50 & 16.63 & 9.29 & 16.56 & 2.26\% & 0.42\% \\ Artificial wave (XYZ direction, 0.5 g) & 19.03 & 0.21 & 19.02 & 0.20 & 0.05\% & 5.00\% \\ Artificial wave (XYZ direction, 0.5 g) & 20.68 & 32.26 & 20.63 & 32.22 & 0.24\% & 0.12\% \\ Artificial wave (X direction, 0.75 g) & 29.94 & 2.12 & 29.05 & 2.02 & 3.06\% & 4.95\% \\ Artificial wave (XZ direction, 0.75 g) & 29.13 & 1.19 & 28.85 & 1.18 & 0.97\% & 0.85\% \\ Artificial wave (XYZ direction, 0.75 g) & 31.25 & 48.72 & 31.04 & 48.07 & 0.68\% & 1.35\% \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparison of the maximum displacement response of the tank dome under different working conditions (mm).  
Figure 5: Comparison of acceleration response of non-isolated and isolated tanks: **(a)** Wolong wave (XZ directions, 0.25 g); **(b)** Wolong wave (XYZ directions, 0.25 g); **(c)** Wolong wave (X direction, 0.5 g); **(d)** Wolong wave (XZ directions, 0.75 g).