Flexural Strength of Ice With Non-Uniform Thickness

A test program has been carried out to investigate the influence of non-uniform thickness on the flexural strength of ice. Over 250 cantilever beams were tested using model ice which had either uniform thickness, or non-uniform thickness. The results were analysed in two different, but complementary methods. In the first method, the flexural strength was calculated based on the maximum, minimum and average thickness of the beam. This was compared to the strength of the ice as determined in uniform ice. The second method computed the "effective" thickness of the non-uniform ice with a strength equal to the strength of the uniform ice. Both techniques clearly showed that the best correlation between the uniform and non-uniform ice was found by using the maximum thickness to characterise the non-uniform ice. An analysis of the data shows that a value of 95% of the maximum ice thickness provides the best representation of the thickness of non-uniform ice failing downwards in flexure. Introduction It is well known that ice thickness plays an extremely important role in the magnitude of the load that an ice sheet can exert on an offshore structure. Numerical and analytical models, which have been used to predict ice loads on sloping (or inclined) structures such as cones, usually have a functional dependence of ice load with a thickness-squared relationship for flexural ice failures (Edwards and Croasdale 1976; Croasdale 1980; Ralston 1977: Kato 1986; Hirayama and Obara 1986; Nevel 1992). For level ice conditions, these models can usually be used satisfactorily to determine the load that the ice sheet will exert on the structure. However, in most real situations, the ice thickness is not at all uniform - it can have a wide spatial variation.