On a shifting pressure-area relationship for the accidental limit state analysis of abnormal ice actions

Abstract

The relationship between pressure and area is often used to describe various ice-structure interaction processes. With knowledge of the nominal contact area and the force, a continuous plot of average pressure versus variation in area during an ice-structure interaction process can be developed. Although debated, it is generally accepted that for Ultimate Limit States (ULS) design, average pressure decreases with increasing contact area. However, this decreasing trend may not be valid for the situations in which the structure can undergo substantial deformations, i.e. Accidental Limit States (ALS). In this paper, by means of nonlinear finite element analysis, it is shown that for ALS design, it may not be necessary for the structure to resist loads corresponding to the conventional ice pressure-area relationship. The pressure is limited either by the ice strength or by the structural resistance. Attention must always be paid to selecting the appropriate ice pressure-area relationship for ALS design. In situations where the structure resistance limits the pressure, the shape of the ice matters. Sometimes the pressure limitation may alternate between the structure- and the ice strength, and the process becomes more complex. How to address this behavior will also be discussed in the paper.