A Simple Remedy for Elephant's Foot Buckling in Cylindrical Silos and Tanks

Abstract

Metal silos and tanks are susceptible to an elastic-plastic instability failure at the base boundary condition which is known as “elephant's foot buckling”, due to its characteristic shape. This form of buckle occurs under high internal pressure accompanied by axial forces in the shell structure. Current international standards for both the static design and earthquake design include a provision to ensure that this failure mode is prevented. However, the only available remedy is currently to increase the wall thickness of the bottom course or strake. In this paper, an alternative method of strengthening against elephant's foot buckling is explored in which a light ring stiffener is used at a critical location. The strengthened shell is analysed using linear elastic bending theory in this preliminary study. Within the scope of this research, the strengthening effect is shown to be sensitive to the size and location of the ring stiffener. Rings that are too small and rings that are too large both cause the strengths to be lower than that when the optimal ring size is used. This is, therefore, an interesting example of structural behaviour in which the provision of a larger amount of material than the optimum leads to reduced strength.