Many parts of a ship, such as bototm structures, decks, and bulkheads consist essentially a plate-stiffener combinations with rectangular boundaries under the action of lateral loads. The stiffener or beam system may consist of orthogonally intersecting beams or beams running in one direction only. The structure may be subjected to lateral loads or it may experience loads in the plane of plating, it may also be subjected to the combined effect of lateral loads in the plane of the plate. The latter two cases involve a consideration of the stability of the system and this report dealt with the problems of plate under lateral loads only. The collapse mode and the corresponding collapse load of stiffened plates were obtained from the experiments and the theoretical calculation. The theoretical analysis were also obtained on the behaviors of stiffened plate above collapse load, and the theoretical calculation are compared with the experiments. The minimum weight calculation was made on orthogonally stiffened plate which was designed by the criterion developed in this paper.