The present designs of ship structures are mainly based on the theories in which deflection of structure is not more than the order of plate thickness. In order to estimate the strength of ship structures when subjected to extraordinary large load, post-yield behavior of ship plates should be investigated. This paper is a theoretical analysis of this problem. Six structural failure modes are identified that are characteristic of the behaviors of ship plates when subjected to very large load. The new formulas of the load-carrying capacity for these failure modes are proposed. It is pointed out that energy dissipation due to fracture is small and therefore this effect is not taken into account. It is shown that geometry of loading object has strong influence on the load-carrying capacity of structure. By using these newly developed prediction formulas, it is possible to construct very simple method to assess the strength of a ship in the event of an accident.