Akifumi Nishihata & Hiroshi Saeki, Hokkaido University
Keywords: vertical ice force, ice sheet adfrozen to a structure, flooding
Abstract
In frozen sea waters, when the water level rises with the ice sheet adfrozen to a structure, sea water gathers on the ice sheet near the structures. This phenomenon is called flooding and arises when sea water rises to the ice surface through brine channels and cracks of the ice sheet. Under these conditions, where flooding occurs, the ice sheet functions as a bearing and is affected by elasticity. However, under the conditions where flooding has no influence, the sheet is affected only by buoyancy.
In this research, we logically clarified the upward vertical ice loads acting on the structure due to the rise of the water level when flooding occurs. Also, we made a comparison of ice loads when flooding occurs with when it does not. We have systematically proven the method to gradually decrease ice loads caused by the change in the water level because ice loads are smaller when flooding occurs. In addition, we have experimentally made clear the adfreeze bond strength between various materials and the ice sheet, which is needed for the calculation of ice loads caused by the change in the water level.
1. Introduction
When ice sheet adfreeze to upright structures, such as piles, bridge piers and intake towers constructed in rivers, lakes, reservoirs and on coasts in cold regions, ice forces act on these structures in a vertical direction due to fluctuation in water levels. Also, even when ice sheet do not adfreeze, due to fluctuation in water levels, vertical ice forces sometimes act on structures whose contact surface with an ice floe is inclined. Reports in the past have described piles of pier structures which were pulled out and intake towers that collapsed by such ice forces. Therefore, when designing structures which can be affected by ice action, it is necessary to consider such vertical ice forces.
Theories of vertical ice forces acting on upright structures and methods to calculate these ice forces have been reported by Kerr1),Christensen 2)and Nakazawa3). However, there have been few detailed studies on flooding conditions.
In this study, we include flooding to calculate the vertical ice forces under various conditions, we compare these forces with cases without flooding, and we investigate methods to reduce the ice forces.
2. Vertical ice forces without flooding
2-1. Deflection of floating ice sheet
The deflection of floating ice sheet is given by the following equation,
where W =deflection in distance r, Kw = unit weight of
