Ice Force Prediction Based on Strain-Rate Field

Abstract

The mechanical behavior of sea ice has been found to be strongly dependent on the deformation rate. Consequently, prediction of ice load on arctic structures must include an adequate consideration of the deformation rate and its effects on the ice behavior. Analytical work for ice load prediction has to date been concentrated on obtaining stress fields around the structure, satisfying an “average” strain-rate dependent strength of ice. In other words, the stress field and the strain-rate field are not directly related. Consequently, there is a gap in understanding the relationship between ice loads and ice deformation. This shortcoming has been recognized, and in the last two years, large-scale field experimental programs have been conducted to measure the deformation pattern and rate around large indenters and an actual offshore island. This paper illustrates a procedure by which the strain-rate dependent mechanical properties of ice can be directly integrated into the force prediction method. This method assumes that the strain-rate field around the structure can be estimated from field measurements and relies on the bound theorems of creep analysis. This paper concentrates on a nonimpact condition in a uniform landfast ice field. The load scenario considered is one of initial breaking out. The effects of nonhomogeneities in the ice field are not included.

Ice cover deformations at Adams Island, winter 1982–1983

“…A higher movement rate of 1 .O m/day may occur over short periods of less than 1 day; this gives a total load of 200 MN (average stress of 500 kPa). Bruen and Vivatrat (1984) used a different approximate method, one that gives higher upper bounds of the total loads. The conditions at Adams Island give average stresses of 370 and 800 kPa, corresponding to movement rates of 0.1 and 1 .O m/day, respectively.…”