Assessment of Seismic Behaviour of Large LNG Tanks Considering Soil-Foundation- Structure Interaction

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During the past decades, demand for Liquefied Natural Gas (LNG) tanks has increased. Indeed, the LNG is cleaner and cheaper fuel for power generation compared to oil and coal. The LNG industry is growing rapidly, and many LNG tanks are constructed in seismically active coastal regions; hence, potential damage or leakage due to cracking triggered by an earthquake can result in destructive environmental and safety issues. These LNG tanks are usually built near the seashore to reduce the cost and increase the flexibility of LNG transportation and storage. Often the foundation soil in coastal regions is not capable of bearing the load of such heavy structures. Thus usually, deep foundations are used to support these tanks. Indeed, pile foundations are commonly used for these large tanks to transfer the load to competent ground layers and control the settlement. Generally, assessing the seismic resilience of these critical infrastructures is essential to ensure the availability and security of services during and after large earthquakes. Considering the complexity of the seismic analysis and design of such structures due to the Fluid-Structure Interaction (FSI) and Soil–Foundation-Structure Interaction (SFSI) effects, advanced modelling and analysis are required. This thesis conducts the three-dimensional fully nonlinear coupled SFSI and FSI numerical simulations for LNG tanks using the direct method. The nonlinear time history analysis and free vibration analysis are conducted to assess the seismic safety and dynamic characteristics of LNG tanks under different pile foundation types and liquefiable soil deposits. The fluid-structure interaction effects are captured using a mechanical model, which captures both convective and impulsive hydrodynamic components. Nonlinear kinematic hardening soil model adopted in this study is also verified and implemented to capture the hysteretic damping of the soil and the variation of the shear modulus with the cyclic shear strain developed in the soil. Infinite boundary elements are assigned to the numerical model, and proper interface elements, capable of modelling sliding and separation between the foundation and soil elements, are considered. This thesis conducts the numerical analyses with the help of the High-Performance Computer (HPC) at the University of Technology Sydney (UTS), taking a few weeks to a month for a single analysis to run due to the complexity of the system.
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