Ice forces are the main concern in designing offshore structures such as drilling platforms, translating points, or bridge piers in arctic regions. Even though some results have been obtained by field measurements in recent years, there are still significant gaps in the knowledge of ice forces on structures. In order to fill some of these gaps, the Iowa Institute of Hydraulic Research has undertaken model studies on the investigation of ice forces on vertical piles. Model techniques for the study of ice-breaking phenomena have been developed, and the similarity between the model indications and prototype conditions has been shown. Tests have been completed on the _ relationship of ice forces (ice strength) vs pile diameter, ice thickness, and the relative velocity (strain rate) between ice and structures. The results suggest a formula considering these parameters, which agrees with field measurements and also in part with model investigations in Russia. The suggested formula will be used as a basis for considering other parameters such as temperature, shape of the structure, contact between ice and structure, and scale effects. The model investigations of these additional influences are nearly completed. Simultaneously, studies on the fracture criteria for ice are progressing, which hopefully will lead to analytical investigations of ice-force problems.
The effect of ice forces on structures has been investigated with steadily increasing interest and activity over the last decade. The driving force for these studies has been the discovery of oil and other mineral resources in arctic regions. Parts of these resources are located offshore, and engineering structures, such as drilling platforms and translating points, are affected by the forces of drifting ice fields. These forces are limited by the strength of the ice, which is a function of several parameters such as temperature and salinity of the ice cover, width, inclination, and shape of the structure, the velocity of the ice floe relative to the structure, and the thickness of the ice cover.
The goal of engineers is to find the functional relationship among these quantities. So far, theoretical analysis has not solved this problem, because the fracture mechanism and the failure criterion of ice, as a viscous elastic, anisotropic material, has not been fully established yet. Several investigators, including Peyton, Croasdale,5 Nevel,13 and Schwarz15,16 have measured ice forces on structures directly in the field. The results of these field tests are limited to the data for specific ice conditions and structural dimensions prevailing for the individual tests. The data indicate trends, but do not allow for the development of complete ice-force equations.
