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of the load equation is derived from the solution of an energy-based collision model in which the kinetic energy is equated to ice crushing energy. Ice thickness, ice crushing strength, hull form, ship size, and ship speed are all taken into account. e exural failure of the ice sheet is also considered as the force-limiting state due to the collision. e results are in close agreement with a variety of past studies and operational experience. e forces generated during a glanc- ing impact are represented in ways that allow them to be used in developing scantlings for individual structural elements, grillages, and supporting structures. Although most traditional ship structural rule formulations are based on elastic criteria, the Requirements Concerning Polar Class incorporates plastic design criteria. Using plastic design can help provide a better balance of material distribution to resist design and extreme loads. is is particularly important because extreme ice loads can be considerably in excess of design values. is is more likely for ice loads than for wave loading. e use of plastic methods should provide a considerable strength reserve, which may or may not be the case with elastic design. e selection of structural design criteria for plastic design is more dicult than in elastic design of which the rst onset of yield is relatively easy to predict, and thus oers a simple crite- rion for design. In plastic design, there are many possible limit states ranging from yield through a nal rupture. e selected design limit state represents a condition of substantial plastic FIGURE . DESIGN SCENARIO: CRUSHING CONTACT AND FLEXURAL FAILURE DURING GLANCING COLLISION January 2011 www.sname.org/sname/mt