ISO 19906 ice crushing load design extension for narrow structures

For ice crushing against a vertical structure the application of the new International Organization for Standardization (ISO) 19906 ice load design code is limited to structures having their width larger than twice the ice thickness (larger than 2 aspect ratio). However, in sub-arctic environment many offshore structures fall well below this aspect ratio limit. To cover this handicap an adjustment to the ISO crushing requirement is proposed. Over 35 year long ice load design practice and subsequent in-field experience of Finnish aids-to-navigation is compared to ISO crushing load design. With decreasing aspect ratio the ISO approach would have resulted in unsafe design. The reason can be attributed to the too weak aspect ratio effect in the ISO database derived from measurements on wide structures. With a simple aspect ratio effect correction the ISO method can be extended also to narrow structures.