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Many engineering problems require an estimate of ice thickness, either the maximum likely thickness or the thickness at some time during the winter. This can be for estimating ice forces on an offshore structure in the sea or a bridge pier in a river. Operation of icebreaking ships requires knowledge of ice thickness to establish the viability of transit to northern ports. Similarly, over-ice transportation on seas, lakes or rives depends on a knowledge of ice thickness. At some locations historical records can be used to estimate ice thicknesses, but with changing climate historical records have limited applicability. Having means for predicting ice growth during a winter is a helpful tool. In high Arctic regions it is assumed the primary factors affecting ice growth are air temperature and snow depth. Assessment of the equations against data from Arctic weather stations indicates that the incorporation of snow depth in terms of a mean annual snow depth is a simple means for improving their predictive capability. Modified equations including mean annual snow depth and freezing degree days as input parameters are proposed and tested against available data at two locations in the Canadian High Arctic; Resolute Bay in a marine coastal environment and Baker lake in an inland freshwater lake. These modified prediction equations are proposed for general application in the Arctic., 24th IAHR International Symposium on Ice, June 4-9, 2018, Vladivostok, Russia

The 25th International Conference on Port and Ocean Engineering under Arctic Conditions, June 9-13, 2019, Delft, The Netherlands

International Conference on Performance of Ships and Structures in Ice (ICETECH), 28-31 July, 2014, Banff, Alberta

Although many studies have been carried out using field, laboratory and analytical methods, uncertainty remains in the magnitude of forces generated by ice ridges on offshore structures. Norstro msgrund lighthouse, located in the Bay of Bothnia in the Baltic Sea, is a cylindrical concrete structure with a sand filled caisson foundation and a waterline diameter of about 7.5 m. It was instrumented to measure ice forces from 1999-2000 for the LOLEIF project, and from 2001-2003 for the STRICE project. Instrumentation included load panels around one half of the structure for direct measurement of ice force, a tiltmeter for assessment of lighthouse tilt motion, and devices to record ice thickness at the site. Load panel and tilt meter data have been analysed to assess global force on the lighthouse during several first-year ice ridge or hummock field interaction events in late winter and early spring of the years 2000, 2002 and 2003. Ridges were encountered with maximum consolidated layer thicknesses of 1.1 to 1.5 m, and unconsolidated keels potentially of 8 m or greater draft. Global loads are calculated from the forces recorded by load panels, and are also interpreted from tilt data. The vertical and horizontal distribution of ice pressures is examined. Most previous publications have focused on the load panels, whose measurement area is limited by their height of 1.6 m. In the present analysis, an attempt was made to assess whether any keel load was measured by the tiltmeter. The forces generated by ridged ice are also compared to those from the surrounding level ice. The methods of the ISO 19906 Standard are applied to predict ice force using the geometry and assumed properties of ridges at Norstro msgrund. These force predictions are compared to the actual measurements, and reasons for discrepancies discussed. The variability in force estimates is examined with reference to the range of possible values for the assumed parameters, including thickness and strength of the consolidated layer, and porosity and cohesion of the keel rubble., International Conference on Cold Climate Technology, 26-28 May 2014, Narvik, Norway

Bureau Veritas has an interest in expanding the Guidelines for ‘Ice Reinforcement Selection in Different World Navigation Areas’ to include a chapter on Greenland Waters. This report contains the chapter for the guidelines and includes: 1) typical ice conditions, 2) selection of appropriate ice class, 3) legislation to be followed and 4) additional interesting meteorological parameters. A short supplement is included that provides further detail on source data and methods.

The CCGS Terry Fox field trials produced impacts with growlers, bergy bits and a small iceberg over a range of velocities. Ice mass ranged from 30 t to 22,000 t and velocity from 0.1 m/s to 6.6 m/s. Results have been analysed looking at the effect of speed and ice mass on the measured impact force. There was considerable scatter in the results until the rate of the rise time of the measured impact force was taken into consideration. A trend of increasing impact force with loading rate was observed. To further examine this aspect of rate effect on impact forces, medium scale field indentation tests were also studied, since they were done to simulate full scale impact loading. The tests were done at a number of locations in the Arctic on iceberg ice and multi-year ice, and also showed a rate effect. For the CCGS Terry Fox the maximum force related to the loading rate with the following expression where F is force in MN and is loading rate in MN/s. The expression is supported by data up to a maximum force of 6 MN. Higher forces at comparable loading rates were achieved in the field indentation tests due to higher loading system capacity and better ice-indentor contact.

Ice interactions with the Confederation Bridge for the winters 2008, 2009 and 2010 have been studied. Tilt data from piers P23 and P24 in response to ice and wind actions were recorded by a data acquisition system. Video records of ice interactions with pier P23 and overall ice conditions adjacent to piers P23 and P24 allowed ice conditions and interaction processes to be related to tilt measurements. Wind data were also analysed to correct for the tilt caused by wind actions on the bridge. An ice loading scenario of slow build up of ice force on a pier due to the action of current and wind on a large ice floe was identified. In one instance this resulted in a maximum force of about 4 MN being generated on simultaneously on each of piers P23 and P24.

A Joint Industry Project has been carried out to develop a "Catalogue of Local Ice Pressures". The focus of the project was to determine average local ice pressures on various sizes and shapes of design areas, and to present the data in a form to facilitate probabilistic estimation of local ice pressures. The data are organized in a database to assist extraction of local ice pressures as a function of operational factors and ice conditions. The database includes four digital data sets on ship trials (1994 Louis S. St. Laurent, 1991 and 1996 Oden, and 2001 Terry Fox), two offshore structures (1985-86 Molikpaq caisson and 1990 JZ-20-2-1 jacket structure) and one field test (1995 Grappling Island). An example of the method used to process data from bow measurements during the 1994 Polar transit of the Louis St. St. Laurent is presented.

A probabilistic analysis is made to predict the seasonal evolution of first-year ice loads on the Molikpaq offshore structure throughout a winter in the Canadian Beaufort Sea. The analysis is based solely on the failure modes of the ice, the ice thickness, and the number of weekly ice loading events. The paper illustrates the use of the probabilistic approach using these basic input values. The results of the analysis show good agreement with the measured ice loads on the Molikpaq in the Beaufort Sea.

A large piece of shore fast ice approximately 5 by 10 km broke free and drifted through Northumberland Strait on April 4 2003, failing against the piers of the Confederation Bridge. The ice had been surveyed shortly before its break-up and its thickness was about 1 m with many ridges of about 4 m thick when averaged over a 20-m diameter. While the ice was quite thick, it was late in the season and thus soft resulting in the maximum force determined on the two piers only in the order of 2 MN. Hand held videos of the episode provided an overview of the ice failure processes observed.

Information on the morphology and properties of first-year ice ridges in the Sea of Okhotsk is required for design of offshore structures. Data have been compiled to provide a picture of Okhotsk sea ice ridges. The data include sail heights, keel depths, consolidated layer thickness, porosity and ridge width. The data from the Sea of Okhotsk are compared with data for ridges from the Beaufort Sea. Okhotsk ice ridges were found to have similar proportions to Beaufort ridges, i.e. ratio of keel depth to sail height is on average 5:1, average sail porosity 35%, and average keel porosity 20%. Sakhalin ridges are smaller than Beaufort ridges, however they are proportionately 25 % wider than Beaufort ridges.

The Confederation Bridge is a unique structure located in an area with temperate but very dynamic ice conditions. An extensive monitoring and research program including ice force measurements was carried out under the auspices of an NSERC Collaborative R&D Grant. In addition, the National Research Council carried out a complimentary program to measure the response to pack ice of two bridge piers adjacent to the navigation span. There were two objectives of the work. One was on the effect the bridge might have on ice conditions and winter navigation, and the other was on the ice loading on the two piers. The largest force measured over 8 winters was 2.4 MN. Interpreted pack ice pressure was estimated to be in the range of 1 kN/m to 10 kN/m., August 19-22, 2007

This paper mainly focuses on establishing a probabilistic model to explore the relationship between local pressures and the global pressure. Both spatial and temporal correlations among the local pressures are considered in the study. A vector autoregressive model (VAR) is applied in this research to include these correlations. The global contact area is divided into a group of local areas. The model is used to illustrate the probabilistic averaging effect from local pressure to global pressure. The duration effect in which a higher load is likely to result from a longer interaction process is also showed using this model. The model is also used to explore the pressure-area relationship and pressure-aspect ratio relationship. The results imply that using the pressure-area relationship and the pressure-aspect ratio relationship alone may not be sufficient for global load estimation., 2006

The Canadian Standards Association (CSA) developed a comprehensive Offshore Structures Standard in the early 1990s. The Code has had limited use in Canada, but S471 General Requirements, Design Criteria, the Environment, and Loads has seen international application. The Code is performance-based; setting overall targets for reliability and provides specific guidance on achieving these targets. The provisions in the CSA Standard for ice loads have been reconciled with the Russian codes such as SNiP and VSN. A comparison of the codes has shown that they predict similar ice loads., 2006

Compressive ice failure is an important aspect in the design of offshore structures in ice environments. The authors concentrate attention on the crushing failure mode. The scale effect is a phenomenon whereby the average pressure decreases with contact area. In classical elasticity, viscoelasticity and plasticity, there is no scale effect. In the case of ice compressive failure, there is ample evidence of a scale effect. Two factors are dominant in this situation. Ice is prone to fracture, thus reducing the volume of material to be crushed, and aiding in the formation of high pressure zones. The second factor in the scale effect is the averaging process that results from the transition from local pressures on small areas (dominated by high pressure zones) to global pressures, where this effect is averaged. The analysis of probabilistic averaging is described with the example of pressures measured on the Molikpaq structure. The implications for design are significant., The 18th International Symposium on Ice, IAHR'06, August 28-September 1, 2006, Sapporo, Japan

During the 1980s extensive offshore geophysical surveys yielded over 100,000 measured ice thicknesses in one area of the Arctic Archipelago. The date and location of these measurements are known and can be compared with ice regime information on Canadian Ice Service ice charts from the same time period. Air temperature data are available from Arctic Weather Stations at Mould Bay and Isachsen, from which ice strength can be calculated. It has been demonstrated that ice cover strength decreases by a factor of 10 from mid-winter to just before break-up. A methodology has been proposed for using all the aforementioned data to make adjustments to the strength factor p* in the CIS Ice Forecast Model for application in aiding ice forecasting in the Canadian Arctic Archilelago.

In 1991 the ODEN made a voyage to the North Pole. An area in the starboard bow of the ship was instrumented with strain gauges to measure local ice pressures. The ship encountered various ice conditions in its voyage, and whenever a threshold strain was exceeded, a 6 to 12 second-long “event” record of strains was made. Based on a finite element analysis of the ship structure the strains were converted to average ice pressures on a 40-sub-panel area, 10 frames wide (8.5 m) by 4 panels high (3.52 m). The bow is a “landing-craft-form”, sloped 22o from the horizontal. There were 784 events and for each of them average pressures on various area and shapes were determined and related to ship speed and ice conditions. A means of predicting probable ice pressures as a function of a “design” area and exposure is presented., 2005

The STRICE project installed load panels on half the circumference of the Norströmsgrund lighthouse in the Gulf of Bothnia to make direct measurements of ice forces. Near continuous measurements and observations of ice conditions were also made. As an adjunct to the project, a high-resolution tiltmeter capable of simultaneously measuring tilt in two orthogonal directions was installed inside the lighthouse for the 2002 winter season in order to assess an alternative means of measuring global ice force. For quasi-static ice loading, the tiltmeter provided a good representation of ice force acting on the lighthouse regardless of the direction from which the forces acted. In the case of dynamic ice loading with frequency components up to 3 Hz, a 7-second moving average "filter" provided a good representation of force components up to 0.5 Hz., 2005

The Amauligak I-65 deployment of the Molikpaq for the winter of 1985/86 provides a good source of local pressure data and a basis for estimating global loads on a wide structure. Data including Medof panel pressures and hourly ice conditions at Molikpaq have been extracted from the “Catalogue of Local Ice Pressures” (CLIP) database. Pressures as high as 10 MPa were experienced on small areas; on areas greater than 3 m2, peak pressures are less than 2 MPa. A method is presented for the calculation of peak loads on the north and east faces, using local ice loads to obtain estimates of global face loads. Extreme values of global ice loads were of the order of 200 MN, with most ice forces during the season being much lower. Thicker ice generally corresponds to higher ice loads on both the east and north faces. However for the thickest ice, lower than expected forces were calculated for the faces of the structure. This could be due to less ice drift (and lower exposure) for very thick ice., 2005

The Japan Ocean Industry Association made available to the IAHR Ice Crushing Working Group one data file from a field test conducted February 4, 1999. An indenter 1.5 m wide by 0.5 m high, penetrated a sea ice sheet 168 mm thick at a rate of 3 mm/s for a total penetration of 1000 mm. The entire indenter face was covered with “tactile” sensor elements, each nominally 10 mm by 10 mm. Spatial distributions of local pressure were recorded throughout the test as well as the total load measured with a load cell. Detailed analysis of the results showed that the load cell and tactile sensors gave comparable results. The tactile sensors showed a “line-like” load distribution with only about 10 % of the ice edge in loadbearing contact. “Hot-spots” of high local pressure persisted for surprisingly long periods, up to 10 s. Local pressure variations tended to be synchronous, that is largely increasing and decreasing with global load., June 21-25, 2004

In 1999 the Canadian Standards Association (CSA) embarked on an initiative to both revise the existing Offshore Standards that were adopted in the early 1990s and move forward to harmonize them with the ISO Offshore Structures Code. The updating process followed a consensus approach with care taken to ensure that due process was followed. Changes to CSA S471 General Requirements, Design Criteria, the Environment, and Loads, which sets the overall principles of the CSA Offshore Structures Code, were small, but there has been extensive revision of the Annex E Determination of ice loads as well as the addition of two new annexes, Annex H Accidental loads and Annex I Ice accretion on offshore structures. The revised CSA Code sets a basis for harmonization with the ISO Offshore Structures Code., May 23-28, 2004

This paper introduces an inertial measurement system called MOTAN and discusses results from one of its full-scale installations. Recent measurements have shown that the MOTAN system offers a novel approach for determining ice-induced global loads on ships. The system consists of two parts: an instrument for measuring whole-ship motions, and software for processing those motions to obtain global ice impact loads. A background of the MOTAN system is given, along with modelscale and full-scale data to support its feasibility for determining global loads from transient ice impacts. The focus of the paper is full-scale data acquired while the CCGS LOUIS S. STLAURENT rammed old ice floes in the high Arctic. MOTAN-derived global loads are presented for three representative events. Data show that ice impact forces can approach 17.3 MN when ships operate in heavy ice conditions., May 28 – 30, 2003

This report provides documentation on the recently updated MOTAN system. The MOTAN uses measured whole-ship motions to obtain the global loads associated with transient ice impacts. Model-scale and full-scale data are used to demonstrate the feasibility of using the MOTAN system to provide reliable information on global loads. Whole-ship motions of the icebreakers HEALY and LOUIS, which have similar ship displacements, are used to determine ice-induced global loads for more than 200 impacts. Results show good agreement between global loads measured on the HEALY and LOUIS. Impacts with warm first-year ice at ship speeds up to 11 kt caused global loads from 1.7 to 7.0 MN. Impacts with medium to thick second-year and multi-year ice at speeds from 0.6 to 16.1 kt resulted in global loads from 1.9 to 17.3 MN. The three highest global loads on the LOUIS (15.7, 16.7 and 17.3 MN) resulted from ramming a rubbled multi-year floe at about 11 kt. The three impacts occurred in quick succession, over a period of about 5 seconds, as the ship slowed to 5 kt from 11 kt. Plotting the initial impact force (the first in a series) versus ship speed showed a clear trend of increasing global load with increasing ship speed, for the multi-year ice events. A lesser correlation was found for thick second-year ice impacts and no apparent correlation for thick first-year and medium second-year ice impacts.

This paper reports on two seasons of field measurements conducted on landfast, first year sea ice in the Canadian Arctic. Field measurements began in mid-May, when the ice was still cold and continued, on a regular basis, until June and July. During the field programs the snow and ice thickness were monitored, as were the ice temperature, salinity and strength of the ice. The in situ ice borehole strength was measured in more than 100 borehole jack tests each season. Measured borehole strength was compared to the calculated flexural strength of the ice. During the period that the strengths overlapped, there was good agreement between trends in the measured ice borehole strength and the calculated flexural strength., February 24-28, 2002

A group of 20 people met for two days in a workshop format to review the state-of-art on ice loads on ship hulls. Measurement methodologies as well as the results of about 15 field trials in which Canada and/or the United States played a major role were reviewed, and the completeness and availability of the data assessed. Needs for ice loads R&D were reviewed and gaps in data and analysis identified. Future directions for R&D and priorities were identified. In addition to this record of the Workshop, presentations and comments by participants are included in 20 files in pdf format on an included CD., Series: Technical Report (National Research Council of Canada. Canadian Hydraulics Centre); no. CHC-TR-001

Providing the whole-ship motions in ice operations was part of the Canadian contribution to the Arctic Ship Technology Research and Development Program conducted on the USCGC Healy. An inertial measurement system was used to measure the whole-ship motions of the USCGC Healy during its Ice Trials, April/May 2000. The system provided time-series traces of ship motions in six degrees of freedom. A variety of loading conditions was sampled, ranging from relatively light ice conditions to backing and ramming in pressured first- year ice and multi- year ice. The ship motions experienced under the different ice conditions ranged from pitch angles of 0.2° to 0.8° and roll angles of 0.6° to 4.9°. A representative case in which the ship rammed a first-year ridge in open pack ice is discussed. During that event, the ship experienced a 0.7° pitch and 4.9° roll. The whole-ship motions during the ridge impact were used to estimate a vertical bow force of 4.3 MN., August 12-17, 2001

This paper describes the results and analysis of one season of measurements of decayed first year sea ice in the central Canadian Arctic. The study was conducted from 21 May to 19 July 2000 during which time the mean air temperature steadily increased from –15°C to a maximum of +7.5°C. The ice was 1.20 m thick when the program began on 21 May and had decreased to 0.83 m thick by 19 July. On average, the ice ablated at a rate of about 23 mm/day during the program. Initially, the average salinity throughout the full thickness of ice was 5.5 ‰. By 19 July measurements showed that the bulk salinity of the ice had decreased to less than 0.5 ‰. The upper and lower surfaces of the ice began to desalinate before the bulk layer of ice. One of the main components of the study was to measure the in situ confined compressive strength of the ice with a borehole jack assembly; 110 borehole jack tests were conducted from 21 May to 19 July. Over the nine-week period, the in situ strength of the ice decreased from 12 to 3 MPa. Measurements showed that the ice maintained a strength of 3 MPa during the last three weeks of the study. The ice continued to ablate during that time. Most of the decrease in ice strength resulted from changes in the physical properties of the ice., August 12-17, 2001

This report describes analysis results of one season of measurements of decayed first year sea ice in the central Canadian Arctic. The study was conducted from 21 May to 19 July 2000. Mean air temperatures steadily increased from �15�C to a maximum of +7.5�C. The ice was 1.20 m thick on 21 May and had ablated to 0.83 m by 19 July. Ice ablation occurred at a rate of about 23 mm/day. The initial bulk ice salinity of 5.5 � had decreased to less than 0.5 � by 19 July. The upper and lower surfaces of the ice began to desalinate before the bulk layer of ice. The confined compressive strength of the ice was measured in 110 borehole jack tests. All strength profiles showed that the in situ ice strength decreased as the decay season progressed. Over the nine-week period, the average full-thickness in situ strength of the ice decreased from 12 MPa to 3 MPa. Most of the decrease in in situ ice strength resulted from changes in the physical properties of the ice. During the last three weeks of the study, the ice maintained a strength of 3 MPa whereas ice ablation continued until the end of the study.

A series of tests was performed at the Canadian Hydraulics Centre to investigate friction between sea ice and various materials such as concrete, steel, wood and ice. The tests examined the effects of the change in the friction coefficient corresponding with the deterioration of material surface, speed, temperature, surface wetness and normal pressure. A carriage translated an ice specimen back and forth relative to samples of various construction materials fixed to the tank floor, while measuring the normal and tangential forces between the ice and the sample surface. Results from the test series indicated that friction was higher at lower speeds and also on rough materials. There was a great deal of variability observed in the instantaneous values of the coefficient of friction. Temperature had a weak effect on the friction coefficient, with slightly higher values of friction at higher temperatures, and there was a weak trend of lower friction with higher contact pressures. The average coefficient of friction of sea ice on smooth concrete, painted steel and sea ice was about 0.05 for speeds greater than 5 cm/s and increased to about 0.1 at 1 cm/s. The average coefficient of friction of sea ice on rough concrete and corroded steel was about 0.1 at speeds greater than 10 cm/s and increased to 0.2 at 1 cm/s.

This report describes the field program undertaken from 21 May to 19 July 2000 to measure the parameters that best characterize the ice decay process. During the field program, thickness of the first-year sea ice decreased from 1.55 m to 0.80 m, at which point the ice was virtually isothermal. The ice freeboard decreased from 60 mm in late May to a negative freeboard (melt ponding) in late July. Desalination was first observed in the surface layer of ice and eventually occurred in the bulk layer of ice, as indicated by the bulk salinity of 5 � in late May and 0.5 � in late July. More than one hundred borehole jack tests were conducted over the sampling period at depths 0.3, 0.6, 0.9 and 1.2 m. The average decrease in ice strength for the four depths was 8.7 MPa over the sampling period, most of which occurred between 4 June and 1 July. The surface layer of ice showed the largest decrease in strength over the sampling period (14.1 MPa to 2.1 MPa). Ice at a depth of 0.90 m had the least amount of change in strength (10.5 MPa to 3.7 MPa). In late July the bulk strength of the ice was only about 27% of what it was in late May.

The Confederation Bridge is a 13 km long structure which spans the Northumberland Strait, connecting Prince Edward Island and New Brunswick. Because of the uniqueness of the structure, an extensive monitoring and research program is being carried out. A complimentary program is being conducted to measure the response of the bridge piers to the effects of drifting pack ice near the center of the Strait. Instrumentation to measure pier tilt was installed inside two piers adjacent to the navigation span. Pier tilt records for the period of February to April 1999 were obtained. Complimentary measurements of meteorological, ice and oceanographic parameters were also made. The method for analysing pier response to ice effects is described and illustrated for a case where the ice is exerting a load on a pier. A discussion of the method for using measured pier response to determine pack ice pressure is given., Proccedings of the 2000 Annual Conference of the Canadian Society for Civil Engineering, London, Ontario

Ice pressure data collected from the 1994 Polar transit of the Louis S. St. Laurent were analysed to determine local average ice pressures as a function of size and shape of area of interest as well as the influence of ice thickness and ship velocity. A probabilistic approach was used to determine annual probability of exceedance of ice pressures. The results indicated a more rapid decrease in pressure with increasing area (exponent –0.7) compared to exponents of –0.4 to –0.5 commonly found in the literature. This is explained on the basis of more frequent loading on smaller hull areas and the definition of area, in this case a design area. areas In terms of ice thickness at the smallest hull area (0.72 m2) average ice pressure was about 1 MPa higher for ice thicker than 2 m compared to ice thinner than 2m. There was no significant affect of speed on local pressures for speeds up to 10 kts, however at speeds greater than 10 kts, the average pressure was about 20% greater.

The impact forces produced by ice floes can be a significant factor in the design considerations for structures off the East Coast of Canada. A test program was carried out in an ice tank to investigate the force levels due to impact of isolated floes with a structure. In the tests, large floes of sea ice with a surface area of up to 60 m2 and thickness over 200 mm were grown. These floes represented actual sea ice floes, since there was no scaling of ice strength properties. These floes, with a mass up to 14 tonnes, were then accelerated to a desired speed (up 0.2 m/s) and allowed to impact against an instrumented test structure. The impact force and local pressures were measured for each impact. Impact velocity, floe mass and floe edge geometry were varied. The highest force levels measured were of the order of 50 kN at a speed of 0.2m/s. A simple analytical impact model was developed and validated with test results. It indicates that the maximum impact force was a function of the kinetic energy of the impacting floe raised to some power less than 1. The exponent and coefficient of the power relation were a function of ice floe edge geometry and the ice crushing pressure relation. Key words: ice forces, sea ice, impact., The Tenth (2000) International Offshore and Polar Engineering Conference: Seattle, USA, 2000

A numerical model of river ice interaction with bridge piers is presented. The model is based on a Particle-In-Cell (PIC) approach combined with a viscous plastic ice rheology. The plastic yield follows a Mohr-Coulomb criterion. The Zhang-Hibler (1997) numerical scheme is used to solve the momentum equations. The model is used in this paper to examine the role of the shape of the structure, ice thickness, ice properties, and velocity on the resulting ice forces. The results show good agreement with field measurements., 2000 Annual Conference of the Canadian Society for Civil Engineering: London, Ont. Canada, 2000

The relation between pressure and area is used to describe various ice-ship interaction processes. Two types of pressure-area relations have been defined. One pressure-area relation describes the process of ship penetration into an ice feature. The other pressure-area relation describes the spatial distribution of pressure at an instant in time. The extensive local pressure data from the Louis S. St. Laurent and the Oden provide useful insights into the nature of pressure-area relations. The cases examined in this paper show that even though the two types of relations demonstrate similar trends of decreasing pressure with increasing area, they are quite different in nature. More examination of data in the context of the process pressure-relation is required before generalizations can be made. There is adequate data for describing the spatial distribution of local pressure as a function of area., August 23-27, 1999.

The Molikpaq steel caisson structure was used for exploratory drilling for four winters in the Canadian Beaufort Sea. During its deployment, it experienced loads from moving ice fields that had a wide range of morphology. A large number of first-year sea ice ridges interacted and failed against the Molikpaq with a variety of different failure behaviour including spine failures, failure behind the ridge, mixed modal, shear failure and stopping of the ridge. This paper reviews these failure behaviours and provides some representative information on the global loads generated during ridge interaction with the Molikpaq. The global loads were on the order of 45 MN to 90 MN which, compared to level ice crushing, are in the low to moderate range., July 6-9, 1999