A Study of Fluid-Structure Coupled Analysis for Large LNG Storage Tanks in Consideration of Uplift

Abstract

With the rising demand for LNG in recent years, expansion of existing LNG terminals and construction of new ones are planned in many places around the world, and some of such projects are already in progress. Sites selected for these projects may not necessarily have favorable soil conditions from the viewpoint of seismic protection. Seismic demand tends to be higher for LNG storage tanks to be built on such sites. Severe seismic deign conditions require precise estimation of the uplift at the annular part during the earthquake. Depending on the estimation results, either of the following measures needs to be taken: increase of the plate thickness; installation of anchors or seismic isolators; and, occasionally, modification of the tank proportion. Uplift estimation is usually based on conventional design methods in which seismic load is converted into static load, because dynamic behavior of uplift is hardly taken into account in the design process due to its complexity. Some previous fundamental studies revealed that tank uplift and other dynamically induced responses would tend to be smaller than those simulated by static loads. This indicates a possibility of optimizing tank structure based on these research results. As a step toward introducing the uplift response in tank design properly, a time-history FEM analysis with fluid-structure coupling was carried out to understand the tank uplift behavior. This paper reports the findings from the analysis, including comparison with conventional analysis and previous fundamental studies. Since the rocking response may reduce overturning moment and base shear of tanks, structural design may have benefits if such mechanisms are properly taken into account.