Recommendations for design of Offshore foundations exposed to ice loads

Report, 2009

A recommendation for better estimations of ice loads on offshore wind power generators is presented together with informative sections on ice loading mechanisms and statistics on ice conditions in Swedish seas. When the foundations are designed horizontal and vertical loads from the ice sheet shall be calculated based on ice thickness, ice strength and properties of the structure. It is then important to distinguish between ice conditions in the landfast ice zone and the more dynamic ice situation further out from shore. As far as measured ice loads on vertical structures are available the probabilistic effective ice pressure (load divided with ice thickness and foundation width) shall serve as guidance. Ice loads against sloping or conical structures can be calculated using plasticity theory only if it is plausible that the ice fails by bending. That is not always the case in areas of pressure ridges or compacted ice. Offshore wind power generators shall be checked for oscillating ice loads if its main frequency can be assumed to be close to the natural frequency of the structure. This applies to both conical and vertical foundations.