The Canadian Equivalent Standards for the Construction of Arctic Class Ships provide a methodology to determine design loads and scantlings for the hull plating and framing members of icebreakers and cargo ships operating in Arctic waters. The design equations explicitly recognize the post yield capacity of the hull structure (plastification of framing and membrane behavior of the plating) under extreme load conditions. This paper summarizes the analytical and experimental work conducted to assess the post yield stability behaviour of typical icebreaker hull panels particularly in regard to the behaviour of the main frames. Two large scale panels, measuring 5000 mm by 2600 mm in plan, representative of a section of the midbody hull structure along the icebelt that extends between the main deck and the bottom structure and between transverse bulkheads of a Canadian Arctic Class 3 (CAC3) vessel, have been tested.
The Canadian Equivalent Standards for the Construction of Arctic Class Ships (Transport Canada, 1995), the background of which is presented in the Proposals for the Revision of the Arctic Shipping Pollution Prevention Regulations (Transport Canada TP9981, 1989), generally call for thinner shell plating and higher strength framing than the 1972 Arctic Shipping Pollution Prevention Regulations. In the Equivalent Standards, for the shell, the elastoplastic behaviour of the required ductile steel is recognized. For the framing the shear strength, bending strength, as well as tripping and buckling stability are explicitly considered. The background report makes the observation that framing stability appears to be not fully understood. In response to this and recognizing the advances in analysis software and computing capabilities work has been performed to investigate the post yield and post buckling strength of typical icebreaking ship midbody side shell structure, with particular focus on the stability of the main frames.
