ABSTRACT

It is well known that ice load predictions are subject to uncertainties. In 1996, a study was undertaken to examine how international experts differed in their ice load predictions, to assess why these differences occurred and to develop a process to help reach consensus on ice loads. The study involved 14 international groups and looked at ice load scenarios involving level and ridged first year ice, multi year ice and driving forces. As expected, the study highlighted significant differences in ice loads as estimated by world-wide experts and organizations. (For example, a factor of 7 between lowest and highest was typical). This paper describes the results of the study, including why differences occurred, areas of consensus reached, remaining issues and recommendations.

INTRODUCTION

The prediction of ice forces is subject to uncertainties. These can be caused by insufficient knowledge of the ice environment, and by a lack of understanding of the processes of ice interaction with structures. The first uncertainty can be addressed by gathering ice data over a several year period (recognizing annual variability). However, the second uncertainty is more difficult to address and is the subject of this paper. Ice interaction processes can be very complex, and involve both ice failure and ice clearing. Ice failure loads are subject to all the uncertainty of how ice behaves as a material as well as the influence of structure shape on failure modes. Physics models for full-scale ice failure have not been proven and are subject to the major difficulty of interpreting small-scale strengths and model tests in their application to larger-scale processes. Despite these difficulties, procedures for ice loads have been developed and are ill use by individual experts, and are quoted in the Codes. However, it is clear that there are still disagreements between experts in ice load predictions.

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