In ISO 19906 (2010), there are no algorithms provided for calculating loads on sloping structures due to interaction with multi-year (MY) ridges; only references are provided for a range of methods; to quote from Clause A."Multi-year ridge actions against conical structures can be estimated using a variety of methods [Croasdale, 1980)], [Nordgren and Winker (1989)], [Wang (1984)]."

A study was undertaken to revisit the theories for breaking and ride-up of MY ridges and if possible to improve them. A new simplified method for long ridges has been developed which includes secondary failures associated with the hinge pieces which are successively broken as the ridge is pushed higher prior to rotation of the broken pieces around the structure. For wide ridges, failure across their width has also been quantified and this mechanism can lower ridge loads compared to prior methods. The new method also recognizes the loads associated with the clearing of level ice fragments ahead of the ridge. The key findings have been incorporated into a methodology which is described by relatively simple equations and these are provided in the paper. Example calculations and sensitivities are provided.

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