In ISO19906 (2010) (Arctic Offshore Structures) specific algorithms are provided for level ice loads on sloping structures; they are based on the separate work of Ralston and Croasdale. These methods were developed decades ago and comparisons with full scale data, especially from Confederation Bridge, suggest that certain idealizations can be improved; more importantly that they may be over-predicting the measured loads. For these reasons it was decided to critically review the existing Croasdale et al algorithm (as specified in ISO) and update it based on learnings from Confederation Bridge, other experience and new ideas.

During the study, over 50 ice interaction events at Confederation Bridge were chosen as geometrically similar to thick ice acting on an Arctic structure. The interaction process and relevant parameters (such as ride-up height) were documented in detail and the measured loads compared with predictions for each event. The model, as currently specified in ISO, generally over-predicted by a factor of about 1.6. The model was improved in the course of the work; especially the physics of breaking and ride-up. The new model is capable of matching the Bridge measurements without bias.

This paper presents the final methodology and equations which resulted from the study which was conducted over several years and resulted in an extensive report and documentation. The equations are closed form and can be applied relatively simply. Examples of using the method are provided. A more comprehensive description of the complete study is given in KRCA (2014) and Croasdale et al. (2016a).

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