Buckling Behavior And Imperfection Sensitivity Analyses Of Vertical Cylindrical Steel Tanks Subiected To Harmonic Settlement

The vertical cylindrical steel tanks are widely adopted in petroleum and chemical fields, which are mainly used for the storage of oil and other chemical products. Considering that the steel tanks are usually located on the soft soils, large differential settlement can be monitored beneath the tank walls. When the differential settlement reaches a critical value, it is prone to cause the buckling of the tank. In this paper, the differential settlement is treated as the form of harmonic settlement. Based on this assumption, the theoretical analyses and numerical calculations are taken to investigate the buckling behavior and imperfection sensitivity of cylindrical steel tanks subjected to harmonic settlement. Main work conducted is as follows:(1) Based on the theory of shell bending with the given model hypotheses, the solutions for two cases are provided:one case is that the vertical cylindrical steel tanks subjected to harmonic settlement, and the other case is that the tank under harmonic settlement and the hydrostatic pressure. Moreover, the buckling formulas are proposed according to the assumption of axial buckling of cylindrical shells.(2) The buckling behavior of cylindrical shells subjected to harmonic settlement is reported. Then, parametric studies are conducted for tanks with various structure parameters, including the height-to-radius ratio and the radius-to-thickness ratio. Besides, the effects of the material models, as well as the top stiffening rings on the buckling behavior are given. Meanwhile, the buckling behavior of floating roof tanks is compared with that of conical roof tanks.(3) The imperfection sensitivity analyses are conducted for steel tanks subjected to harmonic settlement. Three kinds of imperfections are included, such as the imperfections as the form of the buckling mode corresponding to the limit point, dimple buckling mode and the weld depressions. Meanwhile, the worst imperfection for tanks subjected to harmonic settlement is stated. Then, the effects of the circumferential weld depressions on the buckling strength of the tanks are compared with that of vertical weld depressions. Also, the influences of the top stiffening rings and material models on the imperfection sensitivity of the tank are studied.(4) The buckling performance of cylindrical steel tanks subjected to harmonic settlement and hydrostatic pressure are reported. Simultaneously, the impact of the hydrostatic pressure on the settlement-loading capacity of the tank is analyzed. Meanwhile, the effect of the oil pressure inside the tank on the imperfection sensitivity of the tank is provided. Moreover, a method named critical liquid height method is established, which is employed for evaluating the state of the tank subjected to harmonic settlement and hydrostatic pressure.(5) According to the theoretical analyses and numerical results, the critical harmonic settlement rule for tanks subjected to harmonic settlement is preliminarily established. The results predicted by this formula are consistent with numerical results, presenting that this formula is accurate enough for predicting the critical harmonic settlement of the tank. This settlement prediction formula may give structural enginners some references in the future design of the tank.