Plastic Limit Analysis of Sheet Ice Loads on Conical Structures

Abstract

The techniques of plastic limit analysis are used to develop a description of the forces imposed on conical-shaped structures by moving ice sheets. A closed-form solution is presented in which the relative importance of the essential features of the failure process can be clearly viewed. The behavior of broken ice pieces as they move around the surface of the cone is an important design consideration for upward-breaking conical structures. The form of the yield criterion used to describe ice bending strength is not a critical parameter. The largely one-dimensional nature of the ice bending activity near a conical structure does not require an accurate two-dimensional description of ice bending strength. Downward-breaking conical structures offer some advantages in the form of reduced horizontal loads compared to upward-breaking cones. This reduction is largely a consequence of the reduced forces needed to submerge broken ice pieces rather than push them up over the surface of an upward-breaking cone. Additional factors, such as the contribution of the vertical force to the overturning moment and the potential jamming of ice ridges against a downward-breaking cone in shallow water, should also be considered when downwardbreaking geometries are of interest.