Results 1 - 10 of 18035
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[en] The paper reports the results of 105 in situ tests performed on undamaged masonry panels carried out by the authors during the last 20 years. The panels, mostly stone and brickwork masonry, were selected in 59 buildings in Tuscany (Italy) and had different texture and section typologies. The tests, aimed to evaluate both shear strength and deformability parameters, included 50 diagonal tests and 55 flat-jack tests. Main results of tests are supported by a qualitative description of the masonry textures. As a general result, a good agreement was found between the experimental shear strength and the range of values provided by the Italian Building Code. On the contrary, significant differences were obtained with respect to the longitudinal and the shear modules of elasticity. This is probably due to the high sensibility of these values to the method used to treat the data records. The results here presented, together with further data on the subject, are included in a web page named “Tuscany Masonry DataBase”. The database constitutes an effective set of experimental results that can be employed to extract reference values (both quality and mechanical properties) for masonry typologies at local level.
[en] The coupling of Alfven Cascade (AC) modes or reversed-shear Alfven eigenmodes (rsAE) to Geodesic Acoustic Modes (GAM) implies that the range of the AC frequency sweep is reduced as the electron β is increased. This model provides an explanation for the otherwise surprising absence of AC modes in reverse shear NSTX plasmas, given the rich spectrum of beam-driven instabilities typically seen in NSTX. In experiments done at very low β to investigate this prediction, AC modes were seen, and as the βe was increased from shot to shot, the range of the AC frequency sweep was reduced, in agreement with this theoretical prediction.
[en] The effects of the alloying element Re on the ideal strength of γ'-Ni3Al under tensile and shear stresses are investigated using the first-principles method. Results for the stress-strain relationships, ideal tensile and shear strengthes with and without Re addition are presented and explained. Re is found to be effective in improving the strength of Ni3Al. The electronic mechanism underlying the strengthening effects of Re is also elucidated.
[en] Experimental investigations on the impact of multiple drying–wetting cycles on mechanical behaviour of unsaturated soils, particularly on shear behaviour, are limited. Suction-controlled direct shear tests were carried out to investigate the impact of multiple drying–wetting cycles on shear behaviour of an unsaturated compacted clay. One drying–wetting cycle was applied on a soil specimen by increasing its suction to 400 kPa followed by returning its suction to 1 or 200 kPa at constant vertical stress. The experimental results showed that more significant volume contraction occurred during the first drying–wetting cycle as compared with the subsequent drying–wetting cycles. At higher net normal stress (i.e. 200 kPa), a transition from shear-induced contraction to dilation was found. Nevertheless, such transition from contraction to dilation was not observed for the specimens at lower net normal stress (i.e. 50 kPa). The results also showed that amplitude of drying–wetting cycles and vertical stress influences the shear strength. The shear strength increases slightly after the first drying–wetting cycle at lower net normal stress; at higher net normal stress the effect of the first cycle on the shear strength is contrast.
[en] The shear strength of elements reinforced by fibres is predicted by Codes using formulations generally developed from a limited set of test results. In fact, only few of available test results are combined with a material mechanical characterization, allowing to evaluate and compare the different performances of Fibre Reinforced Concretes (FRC). To address this problem, a material-performance-based shear database for FRC elements and their related reference samples in Reinforced Concrete (RC, with and without web reinforcement) is presented herein, merging the experiences carried out in the last decade at the University of Brescia and at the Universitat Politècnica de València. The database is composed by 171 specimens: 93 in FRC and 78 in RC with or without web reinforcement. For FRC elements, the post-cracking resistance (fR,1 and fR,3) is also given according to EN 14651 standard. The evaluation of the shear database was also carried out, discussing the influence of the different factors affecting the shear strength both in FRC and RC samples. Finally, the two formulations suggested by Model Code 2010 for FRC elements are compared against the database results in order to shed new light on code requirements.
[en] Intra aneurysmal hemodynamics such as wall shear stress and complex flow structures have been implicated as one of the important factors on the growth and risk of rupture of an aneurysm. In this study, the sensitivity of intra-aneurysmal blood flow dynamics to the shear thinning rheological model is investigated by using the idealized geometries of a basilar tip aneurysm with two representative anterior posterior (AP) tilting angles (2.deg. and 30.deg.). By choice of different rheological models, time averaged hemodynamic factors such as wall shear stress, oscillatory shear index and relative residence time exhibited only minor effects. However, highly unstable flow present in idealized aneurysm model with 2 .deg. AP tilting angle facilitated an evident change in the instantaneous local flow dynamics with a considerable increase in effective viscosity. Nevertheless, the distinct hemodynamic phenotype, which characterizes the gross intraaneurysmal flow pattern, was independent of the choice of rheological model. This result suggests that the shear thinning viscous effect is of secondary importance in the gross hemodynamics in a basilar tip aneurysm but is appreciably enhanced on the instantaneous hemodynamics with unstable complex flow structures
[en] In geomechanics, constitutive models, which relate strains to stresses, have particular importance. This research concerns with developing a constitutive model for rock discontinuities. A large number of research works in this area have shed light on the most important aspects of the shear behavior of rock fractures. However, the constitutive models have been mostly developed in form of empirical functions best representing the experimental data by means of mathematical regression techniques. Thus, now there is room to upgrade the classic regression methods to the more robust modeling techniques which better capture the nonlinearity of constitutive response. In this paper, the support vector regression (SVR) enhanced with a search algorithm has been employed to construct a constitutive model for rock fractures. A series of 84 direct shear tests was conducted on concrete and plaster replicas of natural rock fractures under different levels of normal stress. The specimens had also different mechanical and morphological characteristics. The SVR constitutive model was developed based on the shear test data. The proposed model indicates significant superiority in estimating the shear strength and peak shear displacement compared to Barton–Bandis model for rock fractures.
[en] A computational survey of the shear strength of 343 unique grain boundaries was performed. For each boundary, the strength was surveyed as a function of shear direction. The results suggest that: (1) the shear strength cannot be comprehensively predicted by common grain boundary descriptors, (2) the shear strength depends significantly and simply on shear direction due to the faceted geometry of boundary planes, and (3) grain boundary shear strengths in an ordinary material can be represented by a simple statistical distribution
[en] We investigate unsteady flow of a thin film of Newtonian fluid around a symmetric slender dry patch moving with constant velocity on an inclined planar substrate, the flow being driven by a prescribed constant shear stress at the free surface of the film (which would be of uniform thickness in the absence of the dry patch). We obtain a novel unsteady travelling-wave similarity solution which predicts that the dry patch has a parabolic shape and that the film thickness increases monotonically away from the dry patch. (author)
[en] In this study the stress–strain characteristics of sand-ground rubber mixtures are investigated in the sandlike zone, at different confining pressures, using hollow cylinder specimens subjected to torsional monotonic and cyclic loading. Under monotonic loading a mixture of sand-ground rubber with 10% and 25% rubber content show more contraction behaviour than that observed in a pure sand specimen. Phase transformation point in these mixtures are located on a larger shear strain. As expected, the shear strength of specimens decreases with increase of ground rubber content. However, with increasing of effective confining pressure, the loss in shear strength of the mixture is decreased. In addition, a mixture with 25% ground rubber shows a smaller loss in shear strength compared to a mixture with 10% ground rubber mixture. Under cyclic loading mixtures with 10% and 25% ground rubber have similar liquefaction resistance, especially at confining pressures of 110 kPa and 260 kPa. Therefore, by using of the mixture with 25% ground rubber, a larger volume of scrap tires could be recycled. The addition of ground rubber to sand would affect the shear strain variation and excess pore water pressure trends, and this effect was further intensified with increasing ground rubber percentage.