An arctic conical-shaped Gravity Based Structure (GBS) will encounter a variety of ice features during its 30–50 year field service life. To study the variation of the ice loads acting on the GBS in the ice contact zone, there are three series of parameters, namely configuration of GBS, ice properties and ice/structure interaction that are on the main focus. The parameters of GBS configurations include cone angle, water/ice line diameter, and ice ride-up height; parameters of ice features consist of ice flexural strength, ice sheet thickness, ice elastic modulus, rubble height and rubble angle; parameters of ice/structure interaction is the ice-structure friction coefficient. These three series of parameters have been systematically investigated to understand the important properties affecting total ice loads.
Ice loads consist of horizontal and vertical ice forces, and overturning moments. For initial sizing of a GBS, formulations given in ISO 19906 provide a detailed reference for calculating ice loads on conical structures under sheet ice loading and is used in this study for ice load calculations. Both methods given in ISO namely the limit state plastic analysis method and elastic beam bending formulations are used and the results are compared. Ice loads due to ice breaking, ice ride-up, ice rubble pushing, ice rubble lifting and ice block turning actions are considered in the elastic beam bending method while forces due to ice breaking and ride-up are considered in the limit state plastic method. Ice features for this study are first year and multi-year level sheet ice. For optimizing a GBS, both ice loads and weight of the GBS are to be minimized. The structure should also have enough stability during installation, and the ability to withstand overturning moments due to ice loads. Constraints are imposed on stability during installation and on the safety factor for overturning, in order to optimize the shape of a conical shaped GBS configuration to have maximum safety with minimum ice loading for design ice features. The optimized cone angle is calculated using ice loads from both formulations given in ISO and for different ice loading conditions.
