Ships operating in littoral sea are likely to be subjected to accidental loads especially stranding. Once she has damage on the hull structure, her ultimate strength will be reduced. This paper is to investigate the effect of stranding damage size on the ultimate strength of ship structure by using a series of collapse tests. For the experiment, five box-girder models of 720mm × 720mm in section and 900mm in length were prepared. Of the five, one has no damage and each four have a diamond shaped damage of different size which represents the shape of rock section in seabed. Among the damaged models, three were made by cutting the plate and one by pressing to represent stranding damage. Experiments were carried out under pure bending load and the applied load and displacements were recorded. The ultimate strength is reduced as the damage size increases, as expected. The largest damaged model has the damage size of 30% of breadth and its ultimate strength is reduced by 21% than that of no damaged one. The pressed one has lower ultimate strength than cut one. This might be due to the fact that the plate around the pressed damage area effect unfavorably on the ultimate strength. The models are analyzed with LS-DYNA and the results are compared with the results from the experiments. From the intact model, buckling occurred in the analysis but not in the experiment. The ultimate strengths of other models from the analysis are fairly close to those from the experiments. The errors are within 10%. With the results from the experiments and analysis, an estimation method of ultimate strength of damaged ship on bottom is derived.

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