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  • 1990-1994  (5)
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  • 1
    ISSN: 1359-5997
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Description / Table of Contents: Resume On évalue la performance en flexion de poutres renforcées de fibres d'acier de différents types et dans des quantités différentes, suivant des paramètres de résilience et des facteurs de résistance résiduelle définis selon la norme ASTM C1018-89. On a examiné cinq types de fibres d'acier dans des proportions allant de 30 à 150 kg m−3, et deux ordres de résistance de matrice, dans un programme de 117 essais sur des poutres larges de 150 mm et épaisses de 100 mm chargées en trois points sur une portée de 750 mm. On a nettement identifié des différences significatives de performance en liaison avec des variations de paramètres de la matrice et des fibres. La résistance à la fissuration initiale dépend essentiellement des caractéristiques qui gouvernent la résistance de la matrice, et minimalement des paramètres de fibre, tels le type, la dimension et la proportion. Les indices de résilience et les facteurs de résistance résiduelle, en particulier ceux qui correspondent aux flexions les plus fortes, dépendent principalement du type et de la proportion de fibre et, pour des fibres de géométrie similaire, des quantités relatives. Tous dépendent minimalement de la résistance de la matrice.
    Notes: Abstract The flexural performance of steel fibre-reinforced beams with varying amounts and types of fibre is evaluated in terms of toughness parameters and residual strength factors determined in accordance with ASTM Standard C1018-89. Five types of steel fibre in amounts from 30 to 105 kg m−3, and two matrix strength levels, were examined in a program of 117 tests using beams 150 mm wide and 100 mm deep loaded at the third points over a 750 mm span. Significant differences in performance associated with changes in matrix and fibre parameters are clearly identified in this test. First-crack strength depends mainly on characteristics that govern matrix strength and is minimally dependent on fibre parameters such as type, size and amount. Toughness indices and residual strength factors, particularly those corresponding to higher deflections, depend primarily on fibre type, amount and, for geometrically similar fibres, aspect ratio. All are minimally dependent on matrix strength.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 1993-01-01
    Description: The Swiss rutschblock test provides practical information about the stability of snow slabs. However, its use by avalanche workers and ski guides is limited by the time required to perform the test and recommended minimum slope inclination (30°). The present study shows how time requirements can be reduced by cutting rutschblocks with cords or specialized saws — faster techniques that do not appear to affect the results. Comparing the rutschblock results with a stability index developed in Switzerland shows that the recommended minimum slope inclination can be reduced to 20°, provided a second person is present to observe the small block displacements associated with slope inclinations below 30°. Sets of rutschblocks on slopes that vary in inclination by 8° or more are used to determine the effect of slope inclination on rutschblock scores. Also, the frequency distributions of six large sets of repeated tests are used to estimate the precision of one or two tests on a uniform slope.
    Print ISSN: 0022-1430
    Electronic ISSN: 1727-5652
    Topics: Geography , Geosciences
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  • 3
    Publication Date: 1993-01-01
    Description: The Swiss rutschblock test provides practical information about the stability of snow slabs. However, its use by avalanche workers and ski guides is limited by the time required to perform the test and recommended minimum slope inclination (30°). The present study shows how time requirements can be reduced by cutting rutschblocks with cords or specialized saws — faster techniques that do not appear to affect the results. Comparing the rutschblock results with a stability index developed in Switzerland shows that the recommended minimum slope inclination can be reduced to 20°, provided a second person is present to observe the small block displacements associated with slope inclinations below 30°. Sets of rutschblocks on slopes that vary in inclination by 8° or more are used to determine the effect of slope inclination on rutschblock scores. Also, the frequency distributions of six large sets of repeated tests are used to estimate the precision of one or two tests on a uniform slope.
    Print ISSN: 0022-1430
    Electronic ISSN: 1727-5652
    Topics: Geography , Geosciences
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  • 4
    Publication Date: 1992-10-01
    Description: Reports of 93 fatal avalanche accidents in Canada between 1972 and 1991 indicate that most of them involved dry snow slabs and were triggered by people. Slab thicknesses averaged 0.86 m and over half the slabs included snow deposited prior to the most recent storm. Two persistent microstructures of snow, namely surface hoar and faceted grains, were commonly reported in the weak layers believed to have released the overlying slabs. The people that had difficulty recognizing or evaluating instabilities involving surface hoar and faceted grains include amateur recreationists as well as professional forecasters and guides. This suggests that present field tests and forecasting techniques may be unsatis-factory for assessing the stability of slabs which overlie layers of surface hoar or faceted grains. Key words : avalanche accident, avalanche forecasting, critical weak layer, slab avalanche, snowpack microstructure, avalanche trigger.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
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  • 5
    Publication Date: 1992-02-01
    Description: A simplified model of an unconfined dry snow slab is used to derive expressions for the rate at which elastic strain energy is released and for the fracture resistance during the propagation of the rapid brittle fractures that result in slab avalanches. A relatively constant energy release rate is derived based on arguments that associate most of the released energy with the crown fracture. In contrast, advancing basal and crown fractures result in increasing fracture resistance. By assuming fracture propagation will stop when the strain energy release rate is just greater than the fracture resistance, the width of a slab avalanche is found to be proportional to an arrest parameter. This parameter includes the slab thickness, slab tensile strength, and basal shear strength, each of which can be measured prior to avalanching. It is argued that, compared to the three variables which can be measured, the remaining variables have limited influence on the width of unconfined slab avalanches. These less influential variables are grouped into an empirical constant that is evaluated using field data from 13 unconfined slab avalanches. The width of these slab avalanches appears to be related linearly to the arrest parameter and to be independent of whether the avalanches result from natural, skier, or explosive triggering. Key words : avalanche, avalanche width, energy release rate, fracture arrest, fracture resistance, slab tensile strength, basal shear strength.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
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