Recent major earthquakes revealed that liquid steel storage tanks are not immune to Natech accidents. The main issue is the potential leakage of hazardous material from the storage tank, which was also the subject of research presented in the thesis. Firstly, the capability of the tank simplified model is investigated by means of a non-code-conforming elevated tank that collapsed during the Kocaeli earthquake. Then three available seismic performance metrics are applied to the non-code-conforming elevated tank and its code-conforming variant. The risk-based performance metric is found comprehensive but computationally demanding, while the conventional performance metric is well established, but it may lead to biased decision-making. This finding implied the development of a computationally efficient simplified model of the unanchored liquid storage tank with a floating roof. The developed simplified model is validated by focusing on simulating liquid overtopping observed from the shaking table test results and refined finite element model. The capability of the simplified model is then demonstrated by means of the seismic fragility and risk analysis of the unanchored broad storage tank with a floating roof. The risk for liquid overtopping is observed high, while the risk for leakage due to tank wall failure is about one magnitude lower. The introduced methodology for seismic risk assessment also accounts for the annual variation of the tank's filling level. It is an efficient tool for loss-of-containment risk management if applied for determination of the risk-based tolerable tank's filling level of the storage tanks.
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