Ice Force Versus Aspect Ratio

Abstract

The calculation of ice forces due to the crushing of solid, competent ice formations such as sheet ice, the consolidated layer of ice ridges and hummocks of solid ice floes involves a number of factors. These are the shape and size of the structure, the thickness and strength of the ice and the ability of the forces driving the ice pack or cover to cause crushing against a structure and the eventual envelopment of the structure by the ice. Only those scenarios where full envelopment of the structure by the ice occurs and where there is crushing of the ice across the enveloped width are considered. The numerical pressure values given are applicable for Beaufort Sea ice conditions. Numerous laboratory tests and full-scale measurements have shown that the ice crushing pressure is dependent on both the aspect ratio and the area of contact. Wide structures generally have large aspect ratios and are subjected to a lower global or average ice pressure. Full-scale measurements show that when ice impacts a wide structure with a large aspect ratio the global ice crushing pressure decreases with increasing ice thickness. The ability of the pack ice to push against a thicker feature such as a ridge fragment or a single, multi-year floe may be the limiting factor in determining the ice force on a structure. Stress measurements in the ice pack show that this pressure can be in the range of 20 percent of the crushing pressure at the ice/structure interface. Missing any of the above elements will result in overestimating or underestimating the ice/structure interaction force.