Table 7-12. Effect of Ice on Marine Structures 



A. Direct Ice Forces on Structures. 



1. Horizontal Forces. 



a. Crushing ice failure of laterally moving floating ice sheets. 



b. Bending ice failure of laterally moving floating ice sheets. 



c. Impact by large floating ice masses. 



d. Plucking forces against riprap. 



2. Vertical Forces. 



a. Weight at low tide of ice frozen to structural elements. 



b. Buoyant upUft at high tide of ice masses frozen to structural elements. 



c. Vertical component of ice sheet bending failure introduced by ice breakers. 



d. Diaphram bending forces during water level change of ice sheets frozen to structural 

 elements. 



e. Superstructure icing by ice spray. 



3. Second, Order Effects. 



a. Motion during thaw of that ice frozen to structural elements. 



b. Expansion of entrapped water within structural elements. 



c. Jamming of rubble between structural framing members. 



B. Indirect Ice Forces on Structures. 



1. Floating ice sheets impinging on moored ships. 



2. Unusual crane loads caused by the difficulty in maneuvering work boats in ice covered 

 waters. 



3. Impact forces by ships during docking which are larger than might normally be 

 expected. 



4. Abrasion and corollary corrosion of structural elements. 



C. Low Risk but Catastrophic Considerations. 



1. Collision by a ship caught in fast-moving, ice-covered waters. 



2. Collision by extraordinarily large ice masses of very low probability of occurrence. 



D. Operational Considerations. 



1. Problems of servicing offshore facilities in ice covered waters. 



2. Limits of ice cover severity during which ships can be moored to docks. 



3. Ship handling characteristics in turning basins and while docking and undocking. 



4. The extreme variability of ice conditions from year to year. 



5. The complacency to be expected by operators in anticipating 100-year occurrences in 

 severity of ice conditions. 



6. The necessity of developing an ice operations manual to outline the operational limits 

 for preventing the overstressing of structures. 



Peyton, 1968 

 7-207 



