Abstract: The plastic theory and numerical simulation method are used to discuss the deformation patterns and collapse mechanisms of stiffeners on the outer bottom plate of a double bottom tanker in a shoal grounding scenario. Numerical simulation technique is used to calculate the deformation patterns and energy dissipation. A mathematical model of the progressively deformed stiffeners is built. With the employment of plastic theory, the analytical expressions of the energy dissipation and the mean resistances are obtained. The analytical results were compared and verified with the numerical simulation results. These analytical expressions can be incorporated to assess the crashworthiness of a ship double bottom during its design phase.