# Seismic Analysis of a Large LNG Tank Considering Different Site Conditions
## 4 Seismic Analysis of a Large Liquefied Natural Gas (LNG) Tank
### Results
The basic natural frequency of solid-liquid coupling decreases with the increase in liquid storage, while the basic natural frequency of liquid sloshing increases with  
Figure 9: The maximum von Mises stress distribution of the outer tank at 100% liquid volume under different site conditions; (**a**) Site class I, (**b**) Site class II, (**c**) Site class III, (**d**) Site class IV. the increase in liquid storage as mentioned in Section 4.3. As a result, the actual tip displacement is less predictable depending on the amount of influence from different contributing factors. Under the same site class, the displacements produced by the three seismic waves are on a similar level. For the same seismic wave, general trends in the displacement graphs are nearly identical for different liquid volume, and the displacement increases with the increase in liquid volume. The maximum displacement in all four site classes reaches 4.78 mm when the tank is filled with 100% LNG under Loma Prieta wave; the minimum displacement is only 0.64 mm when the tank is filled with 25% LNG under Tangshan Aftershock (Qianan) wave. These values again demonstrate that the displacement response of an LNG storage tank varies according to different site classes and different liquid volume. In Class I and Class II, the displacement is nearly identical at the liquid level of 25% and 50%. However, from 50% liquid level to 75% liquid level, the displacement increases significantly. On the other hand, the tip displacements of the LNG tank at liquid level of 25% and 50% under site Class IV are nearly identical to the displacements at liquid level of 75% and 100% under site Class II. In summary, both liquid volume and site condition are important influencing factors in the dynamic analysis and structural design of LNG tanks. When comparing the base shear of the tank at different liquid depths as shown in Figures 12 and 13, both Class III and Class IV are selected to represent the most critical soil types. More specifically, Class III produces the greatest base shear under 75% and 100% liquid levels, followed by site Class IV, site Class II, and site Class I. Class IV produces the greatest base shear under 25% and 50% liquid levels, followed by site Class III, site Class II, and site Class I. When comparing the effect of site conditions on the base shear of the tank, each model is again modelled with 100% LNG as the most critical liquid  
Figure 10: The maximum von Mises stress distribution of the inner tank at 100% liquid volume under different site conditions; (**a**) Site class I, (**b**) Site class II, (**c**) Site class III, (**d**) Site class IV. Figure 12: Base shear of the tank of site Class III under different liquid volume; (**a**) At 25% full, (**b**) At 50% full, (**c**) At 75% full, (**d**) At 100% full. Figure 6:0 Base shear of the tank of site Class IV under different liquid volume. (**a**) At 25% full, (**b**) At 50% full, (**c**) At 75% full, (**d**) At 100% full. Under the same site class, base shear values of the three seismic waves are roughly in the same range. For the same seismic wave, general trends in the base shear graphs are nearly identical for different liquid volume. The variation of peak forces with different liquid volume are also very similar. The maximum base shear in all four site classes reaches \(11.16\times 10^{4}\) KN when the tank is filled with 100% LNG under the Landers wave; the minimum base shear is only \(2.75\times 10^{4}\) KN when the tank is filled with 25% LNG liquid volume under Tangshan Aftershock (Qianan) wave. In addition, the base shear of site Class II only varies slightly for a liquid level of 25% and 50%, but it varies significantly for a liquid level of 75% and 100%. These disparities demonstrate that the base shear of a LNG storage tank is strongly dependent on the corresponding site classes and the liquid level in the tank.