Confined compression tests: Outlining the failure envelope of columnar sea ice

Conical structures are often used to ameliorate the action of floating ice. There is a long history of using cone-shaped bridge piers. Moreover, many recent designs adopt downward-breaking cones to further reduce ice forces. The present work aims to clarify aspects of ice interaction with cones that are poorly understood. This work builds on a previous study that employed a numerical model of ice dynamics in order to predict ice failure patterns and forces on a conical structure. Performance of the model was validated against available ice basin tests, and the study examined a test case representing a pier of the Confederation Bridge, Canada. The present tests examine the roles of ice-structure friction and shape of the cone (upward-or downward-breaking) in more detail. Additionally, the effects of ice thickness and embedded consolidated ridges are examined. The results reveal trends of the dependence of the modes of ice failure and the resulting forces on ice-structure friction, slope and the type of the cone (upward-or downward-breaking). For upward-breaking cones, ice-structure friction proved to be more significant for gentler slopes than for steeper ones. For those cones, ice failure appeared to correspond to three-dimensional buckling. Downward-breaking cones displayed a different behavior with downwards bending failure. The value of the ice-structure friction coefficient had a clear influence on the forces for all downward-breaking cases. The results also support the idea that downward-breaking cones correspond to lower horizontal forces than those acting on upwardbreaking cones. Concerning ice sheet thickness, peak horizontal ice forces show a near linear dependence on the thickness. For large consolidated ridges, forces increased substantially. The numerical model results are compared with the elastic beam bending approach given in the ISO 19906 Arctic Offshore Structures Standard for ice loading on a sloped structure. In order to use the equations in ISO 19906, assumptions must be made on the maximum accumulated rubble height and other parameters, which affect the calculated load. The peak loads from the model and ISO approach are similar for level ice interactions, although the ISO approach is more sensitive to ice-structure friction. Also, the ISO approach may overestimate the load generated by some ridge geometries.

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“…Timco and Frederking, 1986). The tensile and shear strength vanish for that broken ice (C = 0, and = 0).…”

Section: Description Of the Numerical Modelmentioning

confidence: 92%

“… Timco and Frederking (1986) and were shown to produce appropriate ice forces in the validation tests of Barker and Sayed (2012).…”

Section: Simulation Set-up and Test Casesmentioning

confidence: 99%

Conical Structures in Ice: The Roles Friction, Slope and Shape Play

2014

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“…Timco and Frederking, 1986). The ice is allowed to break (or fracture) if normal stress over any part of the ice cover reaches the tensile strength, .…”

Section: Description Of the Numerical Modelmentioning

confidence: 99%

Conical Structures in Ice: Ride-Up, Radius and Results

2015

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As an ice sheet impinges on the surface of a cone, flexural failure takes 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. Previous work by the authors employed a numerical model of ice dynamics in order to predict ice failure patterns and forces on a conical structure. In an initial paper, simulations examined the role of the slope of the cone and the case of ice failure against inverted cones. That study indicated that the slope plays a role on ice loading. Later results, published at ATC 2014, then examined in more detail the roles of structure slope, friction on ice pile-ups and loading on a conical structure and compared the results with the analytical methodology presented in the ISO 19906 Arctic Offshore Structures standard. The present analysis continues to expand the work to examine the role of structure diameter on ice loading and pile-up height. Results are further compared to ISO 19906, with the objective of presenting concrete guidance for the current revision of that standard. Ice forces on upward-breaking cones as a function of structure slope, waterline diameter, ice thickness and ice-structure friction are presented. The results of the study are relevant for structures in ice, such as offshore drilling platforms, bridge piers and offshore wind turbine foundations.

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“…Most recently, Timco and Frederking (1986a) analyzed many of these data for category (a) tests and found that the uniaxial strength of columnar ice could be related to the average stress rate by for horizontally-loaded samples, and for vertically-loaded samples, where a is in MPa, 6 is in MPa s-' (lop3 I k0 I 10") and v, is the total porosity (brine + air) in parts per thousand. Similar expressions have been determined in terms of nominal strain rate.…”

Section: Compressioe Strengthmentioning

confidence: 99%

“…For ice, the failure envelope has been determined by using the combined results of uniaxial compression tests, confined compression tests and shear strength tests both for mostly granular sea ice Frederking, 1983a, 1984), and columnar sea ice (Nadreau and Michel, 1984;Timco and Frederking, 1986a) over a range of loading rates and temperatures. Due to the hexagonal structure of the ice lattice and the horizontal alignment of the c-axis in the columnar ice, there is a marked difference in the failure envelope between the two ice structures (see Fig.…”

Section: Failure Emlopementioning

confidence: 99%