Upward- or Downward-Breaking Cones in Ice: Which One Should You Use?

As an ice sheet impinges on the surface of a cone, flexural (or bending) failure is likely to take place. That ice failure mode causes substantially lower forces than the case of compressive failure, which would take place if ice is to encounter a vertical structure. Some designs further adopt inverted cones, as downward-breaking of ice may produce lower forces. The present study employs a numerical model of ice dynamics in order to predict ice failure patterns, ice clearing around the structure, and forces on the structure. Performance of the model is validated against tests done in the Esso Resources Canada Ltd. ice basin during 1989 and 1990. The paper then proceeds to examine a test case representing a pier of the Confederation Bridge. The results are compared to available observations. Simulations also examine the role of the slope of the cone and the case of ice failure against inverted cones. Comparison of downward-breaking and upward-breaking indicate that the slope plays a role. For a relatively steep slope of 52°, the downward-breaking cone experiences a substantially lower force than the upward-breaking cone. For a gentler 40° slope, the downward- and upward-breaking cones experienced similar values of peak ice forces. The results have applications for bridge pier and offshore wind turbine tower designs, offshore oil and gas exploration and production structures, and standards development, such as the ISO 19906 Arctic Offshore Structures standard, which also has applications for temperate regions.