摘要

The ultimate strength of hull girder is the most important safety guarantee. For a long time, ultimate strength research of ship hull girder is usually under monotonically increasing bending moment. In fact, under extreme ocean wave conditions, the hull girder is more likely to withstand extreme cyclic-bending moments. Under which, the ultimate bearing capacity of the hull girder may be dominated by cyclic buckling failure, extreme low-cycle fatigue failure or the coupling of the two failure modes. In this paper, the ultimate strength and failure characteristics of five steel box girder models are studied under two different kinds of cyclic-bending moments (repeated sagging and alternate sagging/hogging). The two box girder models subjected to alternate sagging/hogging bending moments seem to be fractured due to the extremely low-cycle fatigue. The rest of the three models exposed to cyclic sagging bending moments are collapsed by cyclic buckling accompanying accumulated plastic deformation. The experiment shows that the extreme cyclic-bending moments will significantly reduce the ultimate bearing capacity and fatigue limit of ship girder, and lead to disaster.