Catastrophic failure of the above ground steel storage tanks was observed during past earthquakes, which caused serious economic and environmental consequences. Many of the existing tanks were designed in the past with outdated analysis methods and with underestimated seismic loads. Therefore, the evaluation of the seismic vulnerability of these tanks, especially ones located in seismic prone areas, is extremely important. Seismic fragility functions are useful tools to quantify the seismic vulnerability of structures in the framework of probabilistic seismic risk assessment. These functions give the probability that a seismic demand on a given structural component meets or exceeds its capacity. The objective of this study is to examine the seismic vulnerability of an unanchored steel storage tank, considering the uncertainty of modeling parameters that are related to material and geometric properties of the tank. The significance of uncertain modeling parameters is first investigated with a screening study, which is based on nonlinear static pushover analyses of the tank using the abaqus software. In this respect, a fractional factorial design and an analysis of variance (ANOVA) have been adopted. The results indicate that the considered modeling parameters have significant effects on the uplift behavior of the tank. The fragility curves of two critical failure modes, i.e., the buckling of the shell plate and the plastic rotation of the shell-to-bottom plate joint, are then developed based on a simplified model of the tank, where the uplift behavior is correctly modeled from the static pushover analysis. The uncertainty associated with the significant parameters previously identified are considered in the fragility analysis using a sampling procedure to generate statistically significant samples of the model. The relative importance of different treatment levels of the uncertainty on the fragility curves of the tank is assessed and discussed in detail.
Catastrophic failure of above ground storage tanks was observed due to past earthquakes causing serious economic and environmental consequences. Therefore, the evaluation of the seismic vulnerability of existing liquid storage tanks located in seismic prone areas is an important task. Seismic fragility functions are useful tools in order to quantify the seismic vulnerability of structures. These functions give a probability that a seismic demand on a structural component meets or exceeds its capacity, and are generally derived by a variety of approaches, e.g., field observations of damage, static structural analyses, judgment, or analytical fragility functions. Unlike the other methods, the analytical fragility functions are developed from a coupling of the structural response analysis and a probabilistic seismic demand model. The objective of this study is to investigate the seismic vulnerability of above ground steel storage tanks using different analytical methods of the fragility function. A comparison of the well-known cloud method and the incremental dynamic analysis is performed at different limit states for two existing cylindrical steel storage tanks. The first tank represents a slender geometry with a fixed-roof and the second one is a broad tank, unanchored, and provided with a floating roof.
Steel liquid storage tanks are widely used in industries and nuclear power plants. Damage in tanks may cause a loss of containment, which could result in serious economic and environmental consequences. For the purpose of the earthquake-resistant design of tanks, it is important to use a rational and reliable nonlinear dynamic analysis procedure. The analysis procedure should be capable of evaluating not only the comprehensive seismic responses but also the damage states of tank components under artificial or real earthquakes. The present paper deals with the nonlinear finite element modeling of steel liquid storage tanks subjected to seismic loadings. A reduce-scale unanchored steel liquid storage tank with the broad configuration from a shaking stable test (i.e., the INDUSE-2-safety project) is selected for this study. The fluid-structure interaction problem of the tank-liquid system is analyzed using the Abaqus software with an explicit time integration approach. In particular, the steel tank is modeled based on a Lagrangian formulation, while an Arbitrary Lagrangian-Eulerian adaptive mesh is used in the liquid domain to permit large deformations of the free surface sloshing. The finite element results in terms of the sloshing of the liquid free surface and the uplift response of the base plate are evaluated and compared with the experimental data that is obtained from the shaking table test for the tank under the INDUSE-2-safety project.
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