Implementation of ISO 19906 for probabilistic assessment of global sea ice loads on offshore structures encountering first-year sea ice

Ice failure during ice-structure interactions is a complex process and the development and improvement of ice load models is challenging, in large part because of difficulties obtaining full-scale data and scaling issues when extrapolating from model test data. The ISO 19906 standard provides guidance for the calculation of design ice loads on offshore structures in Arctic and subarctic regions. This paper examines issues in implementing available formulae for probabilistically determining design ice loads from first-year ice on sloping and vertically-faced offshore structures. Methodologies suggested in ISO 19906 are applied to simulate structure interactions with ice floes and embedded ice ridges in subarctic regions, such as the Northern Caspian Sea and Baltic Sea where no multi-year ice is anticipated to contribute to design loads. In these regions design ice loads are determined by first-year ice, which is less severe than the ice loads that result from multi-year ice features in Arctic regions. When compared multi-year ice features, lower ice strength coefficients are appropriate for both first-year level ice and first-year ridges. Structure interactions with first-year ridges are modeled differently than with multi-year ridges. The keels of first-year ridges are not yet consolidated, so that a different model approach is required for keel failure than for the failure of fully consolidated multi-year ridges. Challenges in defining the required input data for the appropriate ISO 19906 formulae are discussed in this paper. Sensitivity analyses performed using the Sea Ice Loads Software (SILS), a Monte-Carlo type simulator developed by C-CORE for determining first and multi-year sea ice loads using probabilistic methods are also presented and discussed. Suggested ISO 19906 models of potential failure modes are implemented in SILS for first-year level ice and ridge interactions with different structure types. The sensitivity analyses compare design ice loads from ice impacts with different structures and for different ice loading scenarios, illustrating the influence of different model assumptions on calculated design loads.