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Structural analysis of big constructions made of snow and ice
2001 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Up to today constructions made of snow and ice, such as the Icehotel in Jukkasjärvi are mainly built based on knowledge achieved by experience. This work is intended to achieve some insight in structural behaviour of snow-constructions using finite element tools, namely FEMGV6 (pre-processing), ABAQUS 5.8 (analysis) and ABAQUS POST 5.8 (post-processing). Used analysis-input values concerning material properties for snow are based on actual knowledge in Snow Mechanics and are based on density of the snow. An overview of the actual state of knowledge in Snow Mechanics based on information found in literature is summarised in a chapter concerning Snow as a construction material. This shows that snow properties are difficult to describe, as they depend not only on the many different snow-types, but are also influenced by metamorphism and loading. Even though it would be more correct to have a relationship between bonding of snow-grains and snow properties, the mainly used way of describing snow is actually done by relating the various features to density of the material. Three Introductory Examples apply finite element tools for a snow beam. The first example (Isotropic, layered & orthotropic snow beam) shows the influence of considering material distribution (layered beam) or material properties (orthotropic beam) on the obtained results compared to an isotropic beam. The second example treats Non-linear analysis of a reinforced snow beam for which two different finite element integration codes, namely implicit and explicit, are applied. The aimed failure type in this example is cracking. Due to the lack of knowledge concerning detailed information of brittle behaviour of snow, several assumptions have to be made for this failure type. The third example concerns Creep analysis of a snow beam. Creep is a very important phenomenon for snow, and has thus an important influence on structures constructed of this material. Even though there exist many creep laws for snow, it is not obvious to integrate one of those in ABAQUS. For this study a simple power law is applied, and as failure criteria is chosen the ultimate elastic tensile strain. Those examples show that it is necessary to achieve better knowledge mainly concerning brittle failure and creep behaviour of snow, what would mean above all reaching a state that makes choice of input values more obvious. Results of these examples could also easily be used to verify whether they would be in correspondence to what could be observed in laboratory testing, or whether there would exist a considerable difference between reality and finite element calculation. Depending on results input values for the finite element analysis could be adjusted. The main part of this work concerns Structural analysis of the Icechurch in Jukkasjärvi. The Icechurch consists of two different shapes, which are analysed separately in this case. Structural behaviour is analysed including only dead load and creep deformation in the calculations. Further are studied influence of different boundary conditions and material parameters. For both shapes are performed 2D- and 3D-analyses in order to point out the importance of doing a three-dimensional analysis in case creep has such a big influence on structural behaviour as for snow. It is observed that above all boundary conditions and assumed viscosity parameters (describing creep behaviour) are of importance for the structural behaviour. Preferring a 3D- to a 2D-model is due to the fact, that ice-walls and ice-pillars are in most cases source for strain and stress concentrations in the snow structure. Another reason is that behaviour of the real structure seems but poorly approximated by a two-dimensional model, whereas three-dimensional models show behaviour, concerning vertical displacement, that is also observed in reality. For further work in this field it is considered important to obtain more detailed knowledge on all parameters describing snow properties. This would also include their dependence on temperature variation, which is mainly important for creep behaviour. Concerning modelling, more accurate results could be achieved with a model considering friction between the structure and its support, for the reason that snow-structures in Jukkasjärvi are not fixed to a foundation but simply placed on the snow-cover on the ground. Their horizontal displacement depends thus on a kind of "freezing adhesion", which has not been treated in this study.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Snow, Finite element analysis, Snow constructions, Creep, Icehotel
Keyword [sv]
URN: urn:nbn:se:ltu:diva-58119ISRN: LTU-EX--01/246--SELocal ID: eb35bd0f-827d-45f8-8156-30771d4290b6OAI: diva2:1031507
Subject / course
Student thesis, at least 30 credits
Educational program
Civil Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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