Behaviour of a long rectangular plate in the post-ultimate strength range under uni-axial thrust is discussed based on the results of elastopiastic large deflection analysis by the FEM. It has been found that deflection of a sinusoidal buckling mode gradually changes to that of a roof mode in the post-ultimate strength range when a thin plate is accompanied by initial deflection of a buckling mode. Also in the case of a thin plate accompanied by initial deflection of a hungry-horse mode, deflection of a buckling mode grows above the buckling load. In this case, however, plastic deformation tends to be localised at a certain part of the buckling deflection while unloading takes place in the remaining part, and this causes rapid reduction in the load carrying capacity beyond the ultimate strength. Such behaviour is reproduced also by applying a simple calculation method.
A number of research works have been performed up to now both experimentally and theoretically on the compressive strength of a rectangular plate representing a local panel of deck and/or bottom plating of a ship structure. In the early times of this kind of research, the objective was focused on evaluation of the ultimate compressive strength of a local panel imposing a simply supported boundary condition. In some researches, the influence of boundary condition is examined regarding both inplane and out-of-plane deformations. However, deck and bottom plates are stiffened by longitudinal stiffeners and transverse frames and have scantlings so that the deck or bottom plating undergoes local collapse prior to its overall collapse as a stiffened plate when extreme loads act on the ship structure. This implies that the longitudinal stiffeners are still sustaining the load after the local panels have attained their ultimate strength.