Seismic Responses Anslysis On Large-scale LNG Tanks With Base-Isolation System

Recently, with the greatly increasing demand of Liquefied Natural Gas (LNG for short) in China, LNG receiving terminals tend to be constructed in high-intensity region. Considering the good stability and security, full containment of LNG is the major form during design and construction. To realize completely domestic design and construction, aseismic research is the key point, which should focus on the seismic isolation technology of LNG storage tanks. In this paper, base isolation models with different product levels were modeled, based on practical engineering, using the finite element analysis software ANSYS. By comparing the dynamic responses before and after the base-isolation, the factors affecting the isolating effect were studied. The results are as follows:The peak internal forces all drop after base isolation at different sites. For the outer tank, the oscillation cycle is short and the time-history curve of internal force is steep. However, for the inner tank and the whole structure, the results are the contrary. After isolation, the relative displacement and acceleration curve of both the inner and outer tank wall is more gentle and the cycle is longer, and the peak values of the relative displacement and acceleration reduce. Moreover, the decreasing amplitude ratio of the outer tank wall is higher than the inner tank.As to the isolating affection, under the same seismic waves at the same site, and after base isolation, the tank with half product level is better than the full tank, the outer tank is better than the inner tank, and the inner tank with half product level is better than the full inner tank.There is good isolating effect when the tank is empty. After base isolation, the internal forces of the whole structure, outer tank and the inner tank all minish to a great degree and the oscillation cycle become longer. Relative to the outer tank, the self-weight of the inner tank is very light. It results that the base shear of the outer tank accounts for90%in the total base shear.Respectively under seismic waves at four different sites, the isolating effects all show well. The decreasing amplitude ratio of the total shear of the whole structure are over60%, in spite of some differences among them.The mechanical properties of isolation bearings significantly affect the isolation effect. The one whose yield force is the lowest owns the optimal isolation effect, because of the minimal internal force and displacement response. Thus, employing isolation layer with a lower yield force is a better choice during design.The decreasing amplitude ratio lowers and the peak dynamic response improves as the seismic intensity increases, under the same isolation parameters. Consequently, the lowered range of internal force and displacement is larger. For this reason, base isolation is also suitable for high-intensity region.Under different seismic waves at the same site, the dynamic responses of the tank with base isolation are different. The seismic response will drop down when the cycle of the seismic waves are similar to the cycle of the tank without base isolation. If the cycle of seismic wave is shorter, the decreasing amplitude ratio tends to decrease, while the decreasing ratio of the internal force of the whole structure are till over50%. It shows a good isolation effect.