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ALE Formulation for the Evaluation of Seismic Behaviour of Anchored and Unanchored Tanks

Estimation of the potential degree of risk for tank failure during an earthquake is very difficult to quantify since the liquid-tank system possesses many different nonlinear behaviour mechanisms which may be triggered simultaneously or separately depending on the characteristics of earthquake, contained liquid properties, fluid depth, dimensions of the tank, roof type, material properties, supporting conditions and stiffness of underlying soil medium. These nonlinear behaviour mechanisms can emerge in the form of elephant foot and diamond shape buckling at the tank wall, rupture at the junction between tank wall and base, buckling at the top of tank and roof, settlement at tank support system and foundation and large amplitude deformations at the base plate. For the case of unanchored tank, in addition to these mechanisms, uplift of tank base, sliding of the tank and successive contact and separation between base plate and foundation can be observed when tank subjects to seismic loadings. The analysis tool used to quantify the tank behaviour has to take into account the effects of all aforementioned factors. Since LS-DYNA is capable of handling complexities associated with the nonlinear transient seismic response of unanchored tanks it is utilized in this study. ALE technique and contact algorithms of LS-DYNA are used to model the coupling of tank and fluid and the interaction between tank base and soil, respectively. The results are compared with the provisions given in tank seismic design codes used in the current practice.

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