Sloshing response of a LNG storage tank subjected to seismic loading

The number of Liquefied Natural Gas tanks is continually increasing. These tanks are very large and their capacity is about 150000[m3]. According to safety standards these kinds of tanks consist of an inner steel shell, containing the LNG, and an outer reinforced concrete shell. Nevertheless, they represent a great risk if they fail during an earthquake. Several types of tank failures have been observed. Tanks may be damaged for different reasons. Large shell hoop tensile stresses, resulting from a combination of hydrostatic pressure and hydrodynamic pressure, due to horizontal and vertical ground motions, could fail the tank. A more common type of failure is known as “elephant’s foot buckling”[3]. This is caused by the large overturning base moments, resulting from the impulsive and convective liquid loading on the tank wall during an earthquake. The high vertical compressive stresses, which develop in the tank wall, may cause the buckling of the structure. The aim of this work is to simulate the seismic behaviour of an LNG tank during an earthquake. The analyses have been performed with Ls-Dyna code using a Lagrangian Conference approach [1],[5]. The applied seismic loads have been registered during a Richter magnitude 7.1 earthquake (Magnitude Moment 6.9). Simulations have shown that fluid motion and fluid-structure interaction are responsible of a failure type known as “elephant’s foot”. 3-D results of the large model (76 [m] in diameter) have been visualized with the support of a multi-wall screen at CETMA Virtual Reality Centre (CVRC). This BARCO visualization system is based on ORAD pc cluster with Digital Video Graphics DVG-10, with tracking and stereo capabilities. The FEM model consists of a flat anchored bottom and a cylindrical metallic wall in contact with the LNG: Diameter Wall high Liquid level Liquid volume Tank mass Liquid mass 76[m] 41[m] 38[m] 172000[m3] 4470[ton] 68954[ton]