Buckling/Plastic Collapse Strength of Ship Bottom Plating

Abstract

To clarify the buckling/plastic collapse behaviour and strength of ship bottom plating, a series of elastoplastic large deflection FEM analyses is performed on stiffened plates subjected to combined biaxial thrust and lateral pressure. A part of continuous stiffened plate is considered for analysis taking into account of symmetry conditions. A series of elastic large deflection FEM analyses is also performed on continuous plating without stiffeners to examine the influence of lateral pressure on the buckling behaviour of plating.It has been found that : (1) When initial deflection is in a hungry horse mode, bifurcation buckling takes place. The buckling strength increases with the increase in applied lateral pressure.(2) The buckling strength is increased also by the stiffeners, which constrain the rotation of panel along its edge. An analytical formula is derived to evaluate the local buckling strength of stiffened plate considering the influence of stiffeners.(3) With the increase in applied lateral pressure, the boundary condition of the panel between stiffeners changes from simply supported condition to clamped condition. This change increases the buckling/plastic collapse strength of stiffened plate.(4) With larger lateral pressure, yielding starts earlier. This reduces the buckling/plastic collapse strength of stiffened plate.(5) Owing to the opposite effects described above, the buckling/plastic collapse strength of stiffened plate takes its maximum value at a certain magnitude of lateral pressure, especially when transverse compression is dominant.(6) The formulae by classification societies give conservative buckling strength under bi-axial compression, and the bottom plating has much reserve up to the ultimate strength even when lateral pressure is acting.