AbstractLarge and small cylindrical shells have long been used as tanks and silos to store materials such as oil and its derivatives. The radius-to-thickness ratio of these shells is 500∶2000; as a result, buckling collapse of these thin-walled structures is of major concern for designers. The present study examined inelastic buckling behavior of cylindrical shells near the base, known as elephant foot buckling. This form of buckling occurs under high internal pressure exerted simultaneously with axial compression. The buckling of cylindrical shells subjected to combined axial loads and internal pressure was experimentally studied and tested and a new method of strengthening steel cylindrical shells using fiber-reinforced polymer (FRP) composite materials is presented. The proposed method was studied by numerical methods using a nonlinear algorithm, and the results were evaluated for resistance to buckling of cylindrical shells. The results provide effective and useful information for use in retrofitting cylindrical shell tanks.