Strengthening metallic cylindrical shells against elephant's foot buckling with FRP

Thin metal cylindrical shell structures such as silos and tanks are susceptible to an elastic–plastic instability failure at the base boundary known as elephant's foot buckling, due to its characteristic deformed shape. This form of buckling occurs under high internal pressure accompanied by axial compression in the shell structure. This is a common failure mode for tanks under earthquake loading. Another common situation is in a silo where the silo wall is subjected to both normal pressures from the stored granular solid and vertical compressive forces developed from the friction between the stored solid and the silo wall. This paper presents a novel method of strengthening cylindrical shells against elephant's foot buckling in which a small amount of fibre-reinforced polymer (FRP) composite, used at a critical location, can effectively eliminate the problem and increase the buckling strength. 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 thickness, height and location of the FRP sheet. The issue of optimal FRP strengthening to allow the shell to attain pure membrane-state deformation is examined in detail as strengthening with too much and too little FRP are both undesirable. Both pinned-based and fixed-based shells are examined and their responses are compared.