The Selection of Design Ice Loads and Design Ice Features For Fixed Structures in the Beaufort Sea

Abstract

As is the case for other environmental conditions, design ice loads for offshore structures are characterized as the extremal loads corresponding to a certain probability level (e.g., annual probability of exceedance or associated return period). In the case of ice loads, the load level can be dependent on a large number of uncertain parameters such as the ice velocity, thickness, geometry, and mechanical properties. The estimation of design ice loads therefore requires deriving the load probability distribution from the probability distributions of the input parameters and an ice-structure interaction model, and then using the result in appropriate extremal analysis models based on the characteristics of the ice loading process.

This paper describes an integrated approach for selecting ice loads based on the above procedure for different loading scenarios encountered in the Beaufort Sea. The calculation of ice load probability distributions is based on a probabilistic approach developed in connection with reliability theory. This approximate approach gives good results, in a small fraction of the computer time required for the commonly used Monte Carlo approach. The method also results in an estimate of the most likely set of input parameters which could give a certain load level. This is useful because it can be used as a basis for selecting a “design ice feature” associated with the design load value. The calculations also result in a set of sensitivity factors which define the relative influence of different input parameters on the load. The approach is illustrated by examples dealing with design ice loads for multiyear floes and first year ice interaction with a fixed structure in the Beaufort Sea.