Study On Box Girder Protective Structure Under External Blast Load

In modern naval warfare, vessels are subject to varies kinds of assail from anti-ship weapon. When detonation occurs outside the vessel and near the strength deck, structural damage caused by blast wave might significantly reduce the capacity of vessels to resist longitudinal bending moment, thus threatening its “after” vitality. Box girder structure, as a new type of protective structure, aims at enhance vitality of the damaged vessels and has been applied in several frigate design.In this paper, the mechanism of box girder structure to improve residual ultimate strength under external blast load is analyzed via numerical simulation. ConWep algorithm in nonlinear finite element software ABAQUS is selected to simulate the blast load on strength deck, and residual ultimate strength of the damaged structure is assessed through quasi-static loading approach. The impact of residual stress due to detonation and material failure definition on residual ultimate strength is evaluated. Mid-section deformation and reduction factor of residual ultimate strength of both common structure and box girder structure are compared in order to find out the anti-explosion mechanism of box girder structure. Finally the impact of plate thickness on anti-explosion characteristics is analyzed. The main conclusion of the research is summarized as follows:1. Structural largre deformation is the main factor which influence residual ultimate strength. The impact of residual stress as well as material maximum plastic strain definition greater than 0.08 on residual strength is minimal.2. Intact ultimate strength of common structure and box girder structure with the same weight is similar. Box girder structure, however, shows significant effect in improving residual strength of damaged ship.3. Box girder structure improves residual ultimate strength by diminishing deformation of strength deck. The mid box girder can be seen as an elastic support in the middle of strength deck, reducing its vertical displacement. The side box girder truncates transverse span of strength deck, enhances stiffness of side grillage, thus reducing deformation of side grillage as well as lower decks.4. In given weight of strength deck grillage, structural anti-explosion capacity can be improved by subtracting more weight from strength deck onto box girder, as well as from side box girder onto mid box girder.