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Flexural Strength of Ice on Temperate Lakes

  • Anthony J. Gow (a1)

Abstract

Large, simply supported beams of temperate lake ice generally yield significantly higher f1exural strengths than the same beams tested in the cantilever mode. Data support the view that a significant stress concentration may exist at the fixed corners of the cantilever beams. Maximum effects are experienced with beams of cold, brittle ice substantially free of structural imperfections; the stress concentration factor may exceed 2.0 in this kind of ice. In ice that has undergone extensive thermal degradation the stress concentration effect may be eliminated entirely. Simply supported beams generally test stronger when the top surface is placed in tension. This behavior is attributed to differences in ice type; the fine-grained, crack-free top layer of snow-ice usually reacting more strongly in tension than the coarse-grained bottom lake ice which is prone to cracking.

Résumé

Resistance a la flexion de la glace des lacs tempérés. De grandes poutres de glace de lacs tempérés sur appui simple produisent généralement des résistances à la flexion significativement supérieures à celles accusées par les mêmes poutres essayées comme des cantilever. Les résultats font penser quéil peut exister une concentration significative des efforts aux points d'encastrement de la poutre. On a constaté les effets les plus importants avec des poutres de glace froide, cassante, dépourvue d'imperfections structurelles; le facteur de concentration des efforts peut excéder 2,0 dans cette sorte de glace. Dans de la glace qui a subi une forte dégradation thermique, l'effet de concentration des efforts peut être entiêrement éliminé. Des poutres à appui simple résistent généralement mieux lorsque la surface supéri eure est placée en tension. Ce comportement est attribué à des différences entre les types de glace: le niveau supérieur à grains fins, non craquelés de glace de neige, réagit d'ordina ire plus solidement à la tension que la glace de lac de la face inférieure de la poutre, à gros grains et prompte à casser.

Zusammenfassung

Biegungsfestigkeit von Eis auf temperierten Seen. Grosse, einfach unterstützte Balken temperierten Seeeises besitzen im allgemeinen beträchtlich höhere Biegungsfesligkeit als dieselben Balken, wenn sie als Kragträger getestet werden. Die Messdaten stützen die Auffassung, dass an den eingespannten Enden der Kragbalken beträchtliche Spannungskonzentrationen auftreten. Maximale Wirkungen zeigten sich an Balken aus kaltem, sprödem Eis, das im wesentlichen keine strukturellen Fehler aufwies; bei dieser Eisart kann der Faktor der Spannungskonzentration den Wert 2,0 überschrciten. In Eis, das starker thermaler Degradation ausgesetztwar, kann der Effekt der Spannungskonzentration völlig verschwinden. Einfach unterstützte Balken erweisen sich im allgemeinen widerstandsfähiger, wenn ihre Oberfläche unter Zugspannung gesetzt wird. Dieses Verhalten ist Unterschieden im Eistyp zuzuschreiben; die feinkärnige, spaltenfreie Oberschicht van Schneeeis leistet gewöhnlich mehr Widerstand gegen Zugspannungen als das grobkörnige Seeeis an der Unterseite, das zur Rissbildung neigt.

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References

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Brown, J. H. 1963. Elasticity and strength of sea ice. (In Kingery, W. D., ed. lee and snow; properties, processes, and applications : proceedings of a conference held at the Massachusetts Institute of Technology, February 12-16, 1962. Cambridge, Mass., M.LT. Press, p. 79-106.)
Butyagin, I. P. 1966. Prochnost’ I'da i ledyanogo pokrova (naturnyye issledovaniya na rekakh Sibiri) [Strength of ice and of floating ice (experiments on Siberian rivers)]. Novosibirsk, l zdatel 's tvo “Nauka” Sibirskoye Otdeleniye.
Frankenstein, G. E. 1959. Strength data on lake ice. V.S. Snow, Ice and Permafrost Research Establishment. Technical Report 59.
Frankenstein, G. E. 1961. Strength data on lake ice. Part II. U.S. Snow, Ice and Permafrost Research Establishment. Technical Report 80.
Frankenstein, G. E. 1968. Strength of ice sheets. Canada. National Research Council. Associate Committee on Geotechnical Research. Technical Memorandum No. 92, p. 79–87.
Gow, A. J., and Langston, D. 1975. Flexural strength of lake ice in relation to its growth structure and thermal history. U.S. Cold Regions Research and Engineering Laboratory. Research Report 349.
Lavrov, V. V. 1969. Deformatsiya i prochnost’ l'da. Leningrad, Gidrometeorologicheskoye Izdatel'stvo. [English translation: Deformation and strength of ice. Translated by T. Pelz. Edited by G. N. rakovlev. Jerusalem, Israel Program for Scientofic Translations, 1971.]

Flexural Strength of Ice on Temperate Lakes

  • Anthony J. Gow (a1)

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