Vertical Ice Forces on Large-Diameter Marine Structuresunder Water Level Changes
Takashi Terashima Pacific Consultants Co., Ltd.
Naoki Nakazawa Ditto
Shinji Kioka Hitachi Zosen Co., Ltd.
Akifumi Nishihata Hokkaido University
Takaharn Kawai Ditto
Hiroshi Saeki Ditto
Abstract
Vertical ice forces, generated by changes in water levels, often act on upright structures built in the ocean, in rivers, and in lakes, as well as on those constructed along beaches, in cold regions. They have pulled out piers of landing stages and bridges, and have collapsed navigation signs.
The theories and computation methods of how these vertical ice forces act on upright structures have been described by such references as Kerr, Christensen, Saeki, Nakazawa, and Terashima. However, few studies have been conducted on inclined large marine structures.
The goal of this study was to accurately compute ice forces to accommodate the design of large structures in frozen sea areas. We clarified the actions of ice forces depending on the form of a structure and on the presence or absence of ice adfreezing to it. We also suggested theoretical solutions and methods to compute vertical ice forces under various conditions.
1. Introduction
Structures, such as piles and foundations, constructed in waters in cold regions, are affected by ice when surrounding waters freeze or when ice floes reach them. Both vertical and horizontal forces can be exerted on these structures. Vertical (upward and downward) ice forces are caused by changes in tidal levels and sudden changes in water levels. Horizontal ice forces are created by such fluid forces as wind, water flow, and waves. Research on ice forces acting on structures in cold regions has been done by Kerr1）, by Christensen2） and by Saeki, Nakazawa, and Terashima3） However, few researches clearly differentiated the influences of the following factors: the form of a structure and the presence or absence of ice adfrozen to a structure.
This paper examines methods to compute vertical ice forces on three special forms of large marine structures constructed in cold regions: cylindrical, conical, and
inverted conical structures, incorporating the presence or absence of an ice sheet adfreezing to a structure and of flooding conditions.
2. Actions of Vertical Ice Forces
Vertical ice forces act differently depending on the form of a structure and by the presence or absence of ice adfrozen to a structure. Their actions can be summarized as follows:
?Cylindrical structures (Figure 1 (a) and (b)): when a structure is upright and is circular cross-sectional, vertical ice forces act only if an ice sheet is adfrozen to a structure.
?Conical structures (Figure 2 (a) and (b)): vertical ice forces act when an ice sheet adfreezes to a structure (a), and when an ice sheet is not adfrozen to a structure but the water level falls (b).
?Inverted conical structures (Figure 3 (a) and (b)): vertical ice forces act when an ice sheet adfreezes to a structure (a), and when an ice sheet is not adfrozen to a structure but the water level rises (b).
Figure 1 Vertical ice forces acting on a cylindrical structure
Figure 2 Vertical ice forces acting on a conical structure
