Isolated ice floe impacts

This paper summarizes all available data related to ice floe impacts on structures. These data include laboratory tests, forces on several bridge piers (Hondo, Pembina, Rideau), forces from small icebergs impacting dedicated test structures (Grappling Island, Newmans Cove), first-year and multi-year ice impacts on the offshore structure Molikpaq, and the Hans Island experiments. The data represent ice masses covering ten orders of magnitude and impact forces covering seven orders of magnitude. The impacts were analyzed using various simple approaches and it was found that the impact force was best related to the kinetic energy of the floe at impact. This energy ranged over thirteen orders of magnitude in value. There was a good correlation of the impact force (F) with the energy (E) at impact with a function form F = A E-0.532 where F is in MN and E is in GJ. The coefficient A was determined to be 61.7 for the likely impact force and 388 for the upper-limit impact force. The reason for this wide range is discussed and related to the wide range of ice strength and failure modes of the ice. The equation is applied to provide guidance on the forces for four different scenarios: (1) river ice impacts on bridge piers, (2) multi-year ice floe impacts on offshore drilling platforms, (3) isolated impact on the leg of a jack-up structure, and (4) impact forces on a Dynamically Positioned drillship with optimization of ice management. The analysis shows that as a rule-of-thumb, the likely impact force in kN is approximately the product of the square root of the mass (in kg) multiplied by the ice floe speed at impact (in m/s). Crown Copyright (C) 2011 Published by Elsevier BM. All rights reserved.