CORRELATION CURVES FOR BRITTLE AND DUCTILE ICE FAILURE BASED ON FULL-SCALE DATA

摘要

The global ice pressure exerted on the face of a structure is examined in this paper, based upon full-scale ice load data collected on the Molikpaq platform offshore the northeast coast of Sakhalin Island. It has been known for a while that when ice fails by crushing against a wide vertically-sided structure, it exhibits a scale effect - namely the average crushing pressure across an area reduces as the size of the loaded area increases. The purpose of this paper is to assess the correlation coefficients between localized ice failure pressures across the face of a wide structure. Depending on the ice failure process, correlations over different distances and time scales are involved. Correlation curves are compared as obtained from the Molikpaq in Sakhalin, the Molikpaq in the Beaufort Sea and the medium-scale JOIA experiments. The results confirm that the interaction velocity, and hence the type of ice failure, has a strong influence on the distribution of ice load. Slow interactions result in ductile or creep failure. This type of interaction results in pressures that are more evenly spread than those involving brittle fracture, which occurs for larger ice drift speeds. As a result, the global ice load for ductile failure is higher due to the simultaneous pressure build-up over the complete face of the structure. Small-scale experiments have proven that the correlation is almost constant with distance during sustained ice-induced vibrations, i.e. during intermittent crushing and frequency lock-in. The paper concludes with a design recommendation for brittle and ductile failure correlation curves. It is the author's opinion that the ISO 19906 global ice pressure equation requires modification to clearly visualize the dependency on the type of ice failure and the compliance of the structure.