The behavior of the double-bottom structure of a ship stranding on a rock is studied to establish the analytical method for the strength. An experiment is performed by using a model of the double-bottom structure of approximately 1/7 scale and a rock model of a cylindrical shape. An analysis using the idealized structural unit method shows a good agreement with the experimental result. A general analytical method to determine the strength of a ship at a stranding condition is proposed. An

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... e calculation is performed for a cargo ship being about 120 m long and stranding on a rock with a cone shape. Furthermore, the nonlinear behavior of a girder element with a manhole is idealized for actual ships and the validity of the idealization is confirmed by an experiment.