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Numerical study of the dynamic soil-structure interaction impact on the seismic response of liquefied natural gas storage tanks

Katsirakis Emmanouil

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Summary

Nowadays, hydrocarbons are the main energy source. Especially natural gas is increasingly taking a leading role energy market. Because of the increasing demand of natural gas, there is an increasing need for its secure storage in liquid form (Liquefied natural gas (LNG)), which is usually stored in large-scale cylindrical steel tanks. In seismic prone countries, such as Greece, when designing such high importance infrastructure the potential seismic risk has to be considered, given the adverse consequences of a failure. However, the earthquake-resistant design of such projects is a difficult task, due to the complex phenomenon of dynamic soil-liquid-tank interaction that occurs during a severe seismic event.In this diploma thesis the dynamic response, including soil-structure interaction, of typical LNG storage tanks was studied. Numerical investigation of the problem has been based on efficient finite element simulations. Initially, the dynamic response of the tank was simulating with fixed base conditions, when it is constructed on rock. Then, a simplified simulation of the soil-tank interaction was performed and the parametric investigation was carried out for different soil types. In all cases the developed displacements, accelerations, stresses and deformations occurring in the examined tank were studied for various excitations, which were suitably selected according to soil conditions. In addition, an additional investigation was conducted for different parameters concerning the liquid content of the tank (filled and empty tank) as well as spectral design accelerations levels (0.24g and 0.36g).The thesis is divided into seven chapters. First chapter presents some general information regarding hydrocarbons and especially LNG, which is the subject of this study. Then, the second chapter presents an extensive description of the different types of storage tanks, as well as the materials and the foundation types used for their construction. In addition, emphasis is given on the description of possible forms of seismic failures occurred in past earthquakes. Third chapter presents some general information with respect to seismic hazard and international seismic norms (EC8, Greek, Indian standards) concerning seismic design of liquid storage tanks. Fourth chapter describes the design methodology for liquid storage tanks and lists EC8 expressions for the calculation of various parameters. Fifth chapter presents a brief overview of the main simulation methodologies of the dynamic response of LNG tanks. Sixth chapter presents the performed parametric investigation as well as a detailed discussion of the obtained results. Finally, last chapter provides the indicative conclusions regarding the seismic behavior of LNG tanks and proposes suggestions for further studies on this important subject.

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