Direct assessment of the tensile strength of the web in prestressed precast hollow-core slabs

The tensile strength of the web concrete in prestressed, precast, hollow-core slabs is investigated by direct measurements on specimens separated from the slabs as cast on the production line. The strength thus obtained tends to be relatively low but consistent and an excellent basis for estimating the shear strength of the slabs.

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Resume On examine la résistance en traction de l'ame de dalles alvéolaires en béton précontraint manufacturé par mesures directes sur des échantillons prélevés sur des poutres lors du moulage à la production. La résistance ainsi obtenue tend à être relativement faible, mais néanmoins elle concorde, et offre une excellente base pour estimer la résistance au cisaillement des dalles.

     

Shear strength of reinforced aerated concrete slabs

The paper reports on the analysis of shear strength of reinforced slabs made of autoclaved aerated concrete without shear reinforcement. The test data are taken from eleven different investigations from six countries, in Europe and Japan, over a period of some twenty years and include 271 tests. The analysis of the test data results in regression expressions, suitably modified from a formula used for ordinary concrete members, and shows good agreement with test values. Appropriate expressions are suggested for design.     

The shear strength index of alpine snow

A shear frame (area 0.025 m²) was used to measure an index of the shear strength of alpine snow. Shear indices were stratified according to snow crystal morphology, and then were correlated with measurements of snow density, temperature, and crystal size. The correlations of shear index with density were significant for all crystal morphologies except for the melt-refreeze morphology. Shear indices correlated erratically with snow temperatures and crystal size.Shear strength was also measured with a large rotary vane (0.5 m diameter). A comparison of rotary vane indices, shear frame indices, and slab avalanche measurements suggests that shear indices decrease with increasing sample size.     

On the rectilinear shear of compressible and incompressible elastic slabs

We review some pseudo-planar deformations for the equations of incompressible isotropic nonlinear elasticity first introduced in 1985 by Rajagopal and Wineman. We extend this class of deformations to compressible isotropic and transverse isotropic materials, and also consider the influence of gravity. We consider some new approximate solutions and we discuss the possible relevance of such solutions to the understanding of the complex structure of the fields equations of nonlinear elasticity, using weakly nonlinear theories.     

Cyclic shear deformation and fatigue of extruded Mg-Gd-Y magnesium alloy

Deformation and fatigue of extruded Mg-8.0 Gd-3.0 Y-0.5 Zr(GW83, wt%) magnesium(Mg) alloy were experimentally investigated under cyclic torsion using tubular specimen fabricated along the extrusion direction. The controlled shear strain amplitudes ranged from 0.606% to 4.157%. Twinning and detwinning of extension twins are observed to take place during cyclic torsion and the shear stress-shear strain hysteresis loops display a perfectly symmetric shape at all tested strain amplitudes. Marginal cyclic softening is observed when the shear strain amplitude is higher than 1.732%. The strain-life fatigue curve shows two kink points, corresponding to the shear strain amplitude of 1.040% and 1.732%, respectively.When the shear strain amplitude is higher than the upper kink point, early fatigue crack is found to initiate on the maximum shear plane. When the strain amplitude is lower than the lower kink point,fatigue cracking is parallel to the maximum tensile plane. At an identical equivalent strain amplitude,the fatigue life under pure shear is much higher than that under tension-compression. The fatigue life of extruded GW83 alloy is much higher than that of extruded AZ31 B alloy at the same plastic strain energy density.     

The shear strength of pretensioned I-beams with debonded tendons

The paper describes a few tests on the shear failure of unitormly prestressed pretensioned concrete I-beams with unreinforced webs and with debonded tendons in the end zones. All the beams were tested under two-point loading. To predict the behaviour of these beams in shear, empirical expressions developed from the test results for conventional beams by others have been used. Most of these formulae are found to overestimate the bearing capacity by nearly 100 per cent. The results show that the bearing capacity of these beams in shear is not completely independent of the number of debonded tendons and their location on the end face of the beam.

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Résumé Des essais ont été effectués afin d’étudier l’effet de la suppression de l’adhérence des cables sur la capacité portante en cisaillement des poutres en béton précontraint à cables adhérents. L’ame des poutres essayées n’était pas armée. Les essais ont été effectués avec une machine d’essai universelle OLSEN 1-MN, les poutres étant chargées en deux points avec une portée d’effort tranchant de 500 mm. La longueur sur laquelle l’adhérence a été supprimée et la longueur de transmission des cables de précontrainte étaient d’environ 600 mm. Un enregistreur automatique a fourni les courbes de fléchissement au milieu des poutres. Ces poutres avaient toutes une longueur de 2,90 m et les essais ont été effectués sur une portée de 2.75 m. On a fait varier le nombre de cables à adhérence supprimée et leur localisation dans la zone d’about des poutres. Toutes les poutres ont été rompues en cisaillement oblique. Pour prédire le comportement en cisaillement de ces poutres, on s’est servi d’expressions empiriques élaborées à partir des essais effectués par d’autres sur des poutres conventionnelles. Les résultats d’essai montrent que, lorsque les cables utiles localisés dans la membrure inférieure gardent leur adhérence, la capacité portante de ces poutres sous effort tranchant augmente de 15%. La suppression de l’adhérence de 50% des cables de la membrure inférieure a déterminé une réduction d’environ 20% de la capacité portante en cisaillement, par rapport à une poutre semblable dont les cables étaient restés totalement adhérents. Les résultats d’essai montrent donc que la capacité portante en cisaillement des poutres en béton précontraint à cables adhérents n’est pas entièrement indépendante du nombre et de la localisation des cables à adhérence supprimée dans la zone d’about de la poutre.

     

Design shear strength formula for high strength concrete beams

After a brief review on the concrete shear strength mechanisms, two very reliable expressions for predicting the shear strength of beams without transverse reinforcement are reported: the one proposed by Ba?ant and Kim [7], which is valid for Normal strength Concrete (NSC) beams, and the other recently proposed by the authors, which is valid for High Strength Concrete (HSC) beams. Hence a summary of a shear strength model for beams with stirrups is provided, which was derived [27] on the basis of the Ba?ant and Kim expression and therefore is adequate only for NSC beams.On the basis of the expression obtained for HSC without stirrups and of the model already proposed for NSC with stirrups, a shear strength expression for HSC beams with stirrups is derived. The obtained expression is applied to an experimental program of 116 HSC beams with stirrups, and is found to predict the test results better than ACI Code [1], Eurocode [12] and CEB/FIP Model Code [9].A design formula is hence proposed, which is adequately conservative and accurate.A design example of a HSC beam with stirrups is carried out, and the various design expressions previously considered are compared.     

Explosive spalling of normal strength concrete slabs subjected to severe fire

The first part of this paper presents an experimental investigation on explosive spalling of six full-scale normal strength reinforced concrete slabs subjected to conventional fire curve ISO834 and severe hydrocarbon fire curve, performed at the Fire Research Centre, University of Ulster, UK focusing on concrete thermal behaviour and the explosive spalling phenomenon. Each slab was loaded with 65% of its BS8110 design load and was heated from the bottom side only. Temperatures profile was recorded at three depths within the slabs and the moisture content was also measured before and after the tests. The deflection of the slabs was recorded at the middle of the 3 m span. The second part of the paper presents a numerical study on the normal concrete slabs using the finite element method. The concrete slabs were modelled including the embedded reinforcement to conduct a non-linear transient structural analysis taking into account cracks appearance and creep. A comparison between the experimental and the FEM results is presented in the paper.     

Longitudinal shear strength of wide compression flanges

This work summarizes a test programme carried out in order to further knowledge of the behaviour of beams with wide compression flanges. The influences of the transverse flange reinforcement and of the transverse bending moment in the flange on the strengths of the beams were studied. On the basis of the test results, commentaries on the ACI and CEB-FIP recommendations for the design of the transverse flange reinforcement are made. An alternative design method is also proposed.

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Resume Cette étude résume un programme d'essais entrepris pour améliorer la connaissance du comportement de poutres à larges membrures en compression. On a étudié influence du renforcement de membrure transversal et du moment fléchissant transversal dans la membrure sur la résistance des poutres. Sur la base des résultats d'essais, on commente les recommandations ACI et CEB/FIP sur le calcul du renforcement de membrure transversal.

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Interlaminar shear strength evaluation of curved composite samples

To assess the bonding quality between the different layers of composite rings fabricated by filament winding it is necessary to choose a useful shear test. A method for measuring the shear strength of thin curved samples is proposed herein. Stress distribution within the probe is calculated and evaluated by finite element method.     

Unified surface anchoring strength from the splay elastic deformation in nematic slabs

Film thickness dependences of the unified surface anchoring strengths from the splay deformation for nematic cells were discussed. Thin nematic parallel (d = 2-50 μm) and wedge (d = 0.3-5 μm) cells with the same solid surface were prepared to evaluate the surface anchoring strength. The surface anchoring strengths from the splay deformations for two kinds of liquid crystals were measured by using the saturation method. The nematogens used were 4-pentyl-4′-cyanobiphenyl and mixture compound ZLI-4792 (Merck Japan Co., Ltd.) with positive dielectric anisotropy. Film thickness dependence of the surface anchoring strength was elucidated on the basis of the conventional ionic surface polarization. It was also discussed that a surface anchoring strength from the splay deformation is to be an intrinsic value defined at an interfacial region and not a value changing with the film thickness.     

Transverse shear modulus and strength of honeycomb cores

The transverse shear mechanical behavior and failure mechanism of aluminum alloy honeycomb cores are investigated by the single block shear test in this paper. The transverse shear deformation process of honeycomb cores may be approximately categorized into four stages, namely elastic deformation, plastic deformation, fracture of cell walls and debonding of honeycomb cores/facesheets. The elastic deformation of unit cell under transverse shear displacement is also investigated by the finite element method, and the result shows that the bending deformation of the cell walls is similar to that of the cantilever beam. In order to precisely predict the equivalent transverse shear modulus and strength, not only shear deformation but also bending deformation of cell walls should be considered. Therefore, in the present paper, the equivalent transverse shear modulus and strength are predicted by application of the cantilever beam theory and thin plate shear buckling theory in conjunction with simplifying assumption as to the displacement in the cores. It is concluded that the contribution of bending deformation of cell walls to equivalent transverse shear modulus and strength is obvious with the decreasing height of cell walls.     

The microstructure of extruded Fe-Al

Five FeAl alloys, whose compositions span the range 34 to 51 at. % Al, were extruded at 1273 K, re-extruded at 1023 K and their deformation structures examined by transmission electron microscopy. The incidence of <1 1 1> slip, compared with <001> slip, was found to increase as Fe-Al became more iron-rich, confirming previous results, in a similar study: some of the <1 1 1> dislocations were found to be present in the form of dipoles. In the most aluminium-rich alloy square <0 0 1> prismatic dislocation loops, planar defects and FeAl₂ particles were observed.