Horizontal ice loads from the level ice on freeze-in into the ice floating structures

Abstract

A lot of interest currently exists towards Arctic region because of huge mineral deposits and unique location for satellite receivers and water-transport constructions. Four-legged and floating concrete or steel offshore platforms are common constructions on the Arctic shelf. Such structures are specially design to resist severe environmental conditions. Usually structures are lifted above the water to decrease the environment actions from ice, waves, currents etc. Ice actions normally considered to be the most important factor for arctic shelf structure design. Most of the normative documents point out that maximum load from the level ice cannot exceed ice failure strength of the corresponding level ice. However, ice actions can vary due to many possible ways of the ice-structure interaction. Some of the possible interactions are not properly described in the normative documents and therefore ice load estimation from different specialists can be different. Resent research show that the estimations from worldwide specialists can vary more than twice. Big uncertainty in the load estimation can lead in one hand to a significant waste of money, or in the other hand compromise the safety of the Arctic construction. One of the reasons for increase of the load from the level ice is structure freeze-in the level ice. Freezing-in the ice during constant water level is not properly described in the existing normative documents and literature, but lead to a significant increase of the load on the structure. When structure freezes into the ice during air temperatures behind freezing point - two factors lead to the load increase. First factor is ice adhesion to the structure and therefore pulling forces occur behind the structure when level ice starts to move. Second factor is accumulation of the additional ice - ¿ice collars¿ on the structure surface behind the water level due to structure high thermal conductivity; this lead to an increase of the structure-ice contact surface, and therefore loads on the structure. Current work proposes method to estimate influence of the freezing-in the ice effect on the horizontal loads from the level ice. Thermodynamical task of the ice growth is presented. Measures to prevent (decrease) horizontal loads from the level ice during structure freeze-in the ice are described in the project.