Ice-induced vibrations and ice buckling

Ice-induced vibrations can occur when flexible, vertically-sided offshore structures are subject to level ice such that the failure mode of ice is predominantly crushing. When the ice is relatively thin, or when the width of the structure is much larger than the ice thickness, the ice tends to buckle and subsequently fail as soon as the stress caused by the buckling exceeds the bending strength of the ice sheet. This type of failure is referred to in this paper as buckling failure. The budding failure can limit the global load on the structure but not necessarily prevents the development of ice-induced vibrations. Study of the latter in cases when ice fails by mixed crushing and buckling is of interest for the design of offshore structures as well as for the interpretation of model-scale tests which often show buckling as a consequence of the use of relatively thin ice. In this study a phenomenological approach for ice crushing and a model of a wedge beam on elastic foundation are combined, thereby composing a simplified model which incorporates both crushing and flexural motion of the ice sheet Typical load signals and a failure mode map generated with the model correspond well with model-scale observations in a qualitative sense. The model predicts that ice-induced vibrations of limited duration can develop as long as the budding failure does not occur within at least one period of intermittent crushing or frequency lock-in. A specific case is discussed for which buckling failure would be expected to occur, but sustained intermittent crushing is observed instead, illustrating that buckling does not necessarily limit the development and duration of ice-induced vibrations, but even the opposite could happen. The possibility for ice-induced vibrations to develop in the regime of mixed crushing and buckling failure is further discussed focusing on the effects of the boundary conditions, structural shape and structural and ice properties. (C) 2016 Elsevier B.V. All rights reserved.