An earlier EU-funded project beside others has shown that the ice forces on marine structures are significantly smaller than presently used for design purposes. Part of this project is full scale measurements of ice forces against a Lighthouse in the Baltic. Within this proposed project it is intended to continue the ice force measurements for three more years in order to increase the quality and quantity of data which is necessary to draw reliable conclusions as a basis for the establishment of new design criteria for marine structures. The ice forces will be compared with the numerical results of an earlier EU-funded project as well as with investigations on this matter presently underway in Japan and Canada.
Measurement of ice forces and ice force effecting parameters during three winter seasons. A data base consisting of selected events with 1. Time series of ice loads, ice thickness, acceleration and inclination2. Video records of ice-structure interaction and ice movement 3. Environmental data and ice maps 4. Set of pictures taken from video camera picture and photo camera 5. log-book with main parameters of ice events (spread sheet file) was established. Data processing of results of collected data 1. raw data collected have been processed, compiled and converted into ASCII format 2. Main events were divided into sub-events, depending on failure mode, ice thickness, ice drift speed etc. and time series were plotted and stored in meta file format 3. Time lap videos were converted from sequential mode into single camera records 4. Additional data evaluation was performed 5. Force data was used to derive a spectral method to model dynamic ice actions. 6. New information on the ice-structure interaction mechanisms. 7. A numerical model for ice-structure contact processes.
Mechanical ice properties The following work has been performed: Sampling of ice cores Compression test of ice Classification data of tested ice: - Compressive strength - Strain rate control - Strength variation - Strain rate effect - Crystal Analysis - Stress-strain curves - Elastic modulus vs. stress level - Mechanical properties of ice blocks sampled - Uniaxial ice strength- Horizontal compressive strength - Vertical compressive strength - Tensile strength As a result a ice strength model has been proposed. Correlation of Data and Predictions The work is based on analyses of full-scale data from the lighthouse Norströmsgrund in the Gulf of Bothnia, Sweden. From 19 February to 11 April 2002, loads and environmental measurements were conducted for 52 days. About 90 % of the monitored interactions between the lighthouse and ice ridges were selected. Characteristics of the 33 involved ridges are given followed by a presentation of the observed failure modes Ridge measurements and models Tests were carried out for the consolidated layer/level ice beside the ridge resulting in the bending strength both in downward and upward loading. Consolidated layer bending downward on top of the underlying rubble resulted in shear failure for cantilever beams. Shear failure occurred beside the loaded area. The unbroken part of the first beam was loaded again resulting in bending failure. In the case of bending failure, whole keel failed quickly during the bending failure and the force decreased rapidly.
Funding SchemeCSC - Cost-sharing contracts
195251 Sint Petersburg
CB2 1PZ Cambridge