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EN
Aeromagnetic data was processed in order to delineate structural trends which may be indicative of potential gold mineral traps in the Watari hill gold prospect located between longitude 5°8''and 5°16'', and latitude 11°24'' and 11°30'' in Garin Hawal district, northwest Nigeria. Landsat-8 OLI data was processed to produce colour composite, band ratio and minimum noise fraction images that mapped the hydrothermal alteration zone in the study area. The multispectral images which were displayed in Red-Green-Blue colours were subsequently pan-sharpened to display a greater image resolution of the area. The application of enhancement algorithms such as an analytic signal to the aeromagnetic data over the alteration zone helped in mapping the mafic metavolcanics, felsic metasediments and intruding granitoid complexes. Further reductions using the second vertical derivative and tilt angle derivative filters aided in delineating fracture/faults and the contact zones of the formations, especially the metasediments-metavolcanic boundary that delineates the shear zone. This study showed that the low-angle geologic structure between the metasediments and metavolcanics where hydrothermal alteration is present is likely to accommodate veins of gold mineralization in the study area.
EN
Strong tectonic remobilisation and shear zone development are typical features of the easternmost part of the Veporicum tectonic unit in the Western Carpathians. The granodiorite mylonites in the area of the Rolovská shear zone (Čierna hora Mts) underwent a complex polystage evolution during the Hercynian and Alpine orogenies. Deformation during the latter reached greenschist facies under metamorphic conditions. Mylonites are macroscopically foliated rocks with a stretching lineation and shear bands. Structurally different mylonite types, ranging from protomylonites to ulramylonites with typical grainsize reduction from the margins towards the shear zone centre, have been assessed. The modal mineralogy of the different mylonite types changes considerably. Typical is a progressive decrease in feldspar content and simultaneously the quartz and white mica content increases from protomylonites towards the most strongly deformed ultramylonites. The deformation had a brittle character in less deformed rocks and a ductile one in more deformed tectonites. Obvious chemical changes occur in mesomylonites and ultramylonites. During mylonitisation, the original biotite granodiorite was depleted of Mg, Fe, Na, Ca and Ba, while K, Rb and mainly Si increased considerably. Other (major and trace) elements reflect erratic behaviour due to lateral mobility. Chemical changes indicate the breakdown and subsequent recrystallisation of biotite and feldspars and, in turn, the crystallisation of albite and sericite. REE decrease in ultramylonites due to the breakup of accessory minerals during deformation and alteration.
PL
Zniszczenie betonu przez ścinanie zachodzi nagle i jest zniszczeniem kruchym. Dodatek włókien stalowych może zmienić charakter zniszczenia na plastyczne zniszczenie giętno-tnące. W badaniach zastosowano samozagęszczający się beton o różnych proporcjach rozpiętości strefy ścinania do użytecznej wysokości przekroju, (a/d), oraz różnych rozstawach strzemion, przy stałej zawartości włókien stalowych równej 0,5% objętości betonu. Wykonano 16 próbek o wymiarach 100×200×1200 mm (rozpiętość przęsła belki 1100 mm) o małej wytrzymałości na ścinanie, którą badano pod obciążeniem trzypunktowym. Badania wykazują, że obciążenie pierwszego zarysowania, obciążenie niszczące jak i wytrzymałość na ścinanie maleją w miarę wzrostu rozstawu strzemion. W wyniku zastosowania dodatku drutu stalowego schemat zniszczenia zmienia się z kruchego zniszczenia ścinania na plastyczne zniszczenie giętno-tnące. Kombinacja włókien stalowych i strzemion korzystnie wpływa na właściwości mechaniczne materiału. Sztywność, nośność i ugięcia belek wzrastają z dodaniem zbrojenia drutem stalowym. Uzyskaną w badaniach wytrzymałość na ścinanie porównano z modelami istniejącymi w literaturze otrzymując zadowalającą korelację wyników.
EN
Of all the different types of failure in concrete, shear failure is a sudden and brittle failure. Addition of steel fibres can modify brittle shear failure pattern to ductile flexural-shear behaviour. In the present study, self-compacting concrete beams were cast by varying shear span to depth and spacing of stirrups with constant steel fibres content of 0.5% by volume of concrete. The size of the beam was fixed at 100x200x1200 mm. The clear span of beam was maintained at 1100 mm throughout the study. A total of 16 shear deficient beams were cast and tested under three point loading. The investigation indicates that the initial cracking load, ultimate load and ultimate shear strength decreases as spacing of stirrups increases. It was also noted that the failure mode has modified from a brittle shear failure to a ductile flexural-shear failure in the presence of fiber. The combination of stirrups and steel fibres demonstrated a positive hybrid effect on the mechanical behaviour of Steel Fiber Reinforced Self-Compacting Concrete (SFRSCC). The stiffness, toughness and deflection of the beams increased with the inclusion of fiber in SCC beams. The shear strength obtained experimentally was compared with the existing models available in the literature, and the correlation is satisfactory.
EN
The article discusses the issues concerning rehabilitation and strengthening of wooden beams in historical naked ceilings in their support area. The causes and effects of the damage in the wooden beams shear zones have been presented. Traditional methods of reinforcing beams along with the examples of their application have been shown. Moreover, modern methods of shear zone rehabilitation as proposed in the literature have been presented. What is more, the article also discusses the proposals of the research program with regard to technological solutions for reinforcing of historical ceiling beams in the shear zone, which will be carried out in the laboratories of the Kielce University of Technology.
5
Content available remote The shear strength of reinforced concrete beams without shear reinforcement
EN
In this article the results of experimental investigations of reinforced concrete (RC) beams on the shear strength are presented. Tests are performed by the improved methodology with testing every beam twice. All experiments are conducted considering different shear span to effective depth ratio. This makes for establishing the impact of the force application position on the carrying capacity of reinforced concrete beams without transverse reinforcement. The result showed the increase of carrying capacity by 8-10% while reducing the shear span to effective depth ratio from d/a=2 to d/a=1,5 and 18-20% while ratio was d/a=1. Calculations by the current standards in different countries showed low compliance with experiment, which is negative for economic design. Carrying capacity calculation method for reinforced concrete beams without shear reinforcement considering loading accommodations as proposed and tested. This factor is not taken into account in Ukrainian current norms of reinforced concrete structures designing. The deviation between theoretical calculation by the proposed empirical formula and experimental data is 10% which provides sufficient reliability of the results for future using.
PL
W artykule zaprezentowano wyniki badań doświadczalnych nośności na ścinanie żelbetowych (RC) belek. Badania zostały przeprowadzone według ulepszonej metodologii, weryfikując wyniki każdej belki dwukrotnie. Wszystkie badania przeprowadzono przy uwzględnieniu różnych zakresów strefy ścinanej w stosunku do efektywnej wysokości przekroju. W ten sposób określono wpływ pozycji przyłożenia siły nośność belek żelbetowych bez zbrojenia poprzecznego. Wyniki badań wykazały wzrost nośności o 8-10 % gdy stosunek zakresu strefy ścinanej do wysokości efektywnej d/a maleje z 2 do 1,5 i 18-20 % gdy stosunek ten był d/a = 1. Przeprowadzone obliczenia nośności na ścinanie według obowiązujących norm z różnych krajów pokazał małą zgodność z wynikami badań, co negatywnie wpływa na ekonomiczne projektowanie elementów. Zaproponowano i sprawdzono eksperymentalnie metodę obliczania nośności żelbetowych belek bez zbrojenia na ścinanie uwzględniającą miejsce przyłożenia obciążenia. Czynnik ten nie jest brany pod uwagę w aktualnych ukraińskich normach projektowych konstrukcji żelbetowych. Różnice między wynikami obliczeń teoretycznych według proponowanego wzoru empirycznego a wynikami badań doświadczalnymi wynosi 10%, co potwierdza wystarczającą dokładność i przydatność do przyszłego użycia.
PL
Zespół Politechniki Białostockiej przeprowadził badania w celu wyjaśnienia możliwości częściowego lub całkowitego zastąpienia strzemion za pomocą stalowego zbrojenia rozproszonego w belkach zginanych. Zbadano trzy serie modeli belek żelbetowych o rozpiętości 1100 mm i przekroju poprzecznym 120 x 80 mm, wykonanych z fibrobetonu o zawartości 1,5% włókien stalowych (objętościowo), zbrojonych na zginanie prętami 2 Ø 8 (o stopniu zbrojenia 1%), o zróżnicowanych obustronnie rozstawach stalowych strzemion. W każdej serii wykonano po trzy belki identycznie zbrojone na zginanie i ścinanie: dwie z fibrobetonu i jedną referencyjną (o symbolach A-O, B-O i C-O) z betonu bez włókien. Wolnopodparte belki obciążano w układzie czteropunktowym, co zapewniło stały rozkład siły poprzecznej na rozpiętości belek. Niemal we wszystkich belkach osiągnięto model zniszczenia przez ściananie. Wyniki badań wskazały na zwiększenie nośności na ścinanie belek z fibrobetonu nawet o 50%, w porównaniu z nośnością belek bez zbrojenia rozproszonego. Okazało się, że włókna stalowe mogą częściowo zastępować zbrojenie strzemionami w belkach żelbetowych.
EN
Team of Białystok Technical University conducted a study in order to clarify the possibility of partial or total replacement of stirrups with steel fibers in bending beams. Three series of models examined reinforced concrete beams with a span of 1100 mm and 120 x 80 mm cross section, made of a fiber- containing steel fibers 1.5% (by volume), the bending reinforcement bars 2 ∅ 8 (with a degree of reinforcement of 1%), with varying spacing on both sides of steel stirrups. In each series were performed identically to the three beams reinforced bending and shear: two fiber-and one reference (with the symbols A-0, B-0 and C-0) of the concrete without fiber. In almost all beams model was achieved by the destruction of the wall. The results showed an increase of shear capacity of fiber-beams up to 50%, compared to the load beam without fiber reinforcement. It was found that the steel fibers can be partially substituted for the reinforcement stirrup concrete beams.
PL
Przedstawiono wybrane wyniki uzyskane z własnych badań eksperymentalnych, dotyczących elementów częściowo sprężonych. Porównano je z wielkościami obliczonymi praktyczną metodą obliczania nośności ścinania zaproponowaną w artykule opublikowanym w "ACI Structural Journal" w nr 3/2010.
EN
Selected results of own experimental tests concerning partially prestressed elements are reported. They were compared with values calculated by practical method of calculation of shear strength proposed by in article published in ACI Structural Journal Vol. 107 No. 3 May-June 2010.
PL
W pracy przedstawiono podstawowe cechy modelu kratownicowego do wymiarowania zbrojenia poprzecznego w ujęciu normy polskiej PN-B-03264:2002 oraz europejskiej PN-EN 1992-1-1:2008. Na tym tle dokonano analizy wpływu otworów w strefie przypodporowej na zachowanie się belek żelbetowych. Podano przykładowe obliczenia na ścinanie belek z otworami okrągłymi, które wykazały, że możliwe są przypadki w których o nośności ścinania będą decydowały betonowe krzyżulce ściskane.
EN
The paper presents basic properties of the truss model for dimensioning of the transverse reinforcement according to the Polish and European standards (PN-B-03264:2002 and PN-EN 1992-1-1:2008). Based on the above the impact of the openings in the shear zone on the behaviour of the reinforced concrete beams was analyzed. The paper includes sample calculations for the shear beams with round openings. It is proven that in some cases the strength for shear may be determined by the concrete compressed struts.
PL
Omówiono podstawowe właściwości modelu kratownicowego do analizy strefy przypodporowej elementów żelbetowych i na tym tle podano procedury obliczania zbrojenia poprzecznego oraz nośności na ścinanie w aspekcie postanowień norm PN-B-03264:2002 oraz PN-EN 1992-1-1:2008.
EN
The basic properties of truss model for analysis of RC elements in shear zone were presented. On this background there were given the procedures of calculating transverse reinforcement and strength for shear, according to PN-B-03264:2002 and PN-EN 1992-1-1:2008 standards.
EN
In the Tatra Mts., thrust-napping and shearing were multi-stage re-activated processes. Their cyclic character was determined by increases and decreases in pore fluid pressure. During each cycle, new parts of the rheologically heterogeneous wall-rock were selectively destroyed due to hydraulic fracturing, brecciation and mylonitization, and moved out as a solution and/or suspension. As a result of these processes, including pressure solution, considerable mass loss could have taken place. All these processes took place under the considerable influence of fluids. In this paper we consider the possible contribution of cavitation erosion to mass loss processes. Displacement along an uneven thrust surface could create chambers filled with fluid and sudden falls in local pressure promoting the inception of cavitation. Cavitation damage, mainly mechanical in nature, could act synergistically with slurry abrasion and pressure solution processes. Our work is of a hypothetical character. To prove the possibility of cavitation erosion within shear zones in the Tatra Mts. we conducted an experiment to show the low resistance of rock samples to cavitation erosion. We also discuss and characterize the conditions essential to induce cavitation within thrust zones at the base of nappes.
EN
The paper focuses on the numerical analysis of the effect of texturial anisotropy on shear localization in cohesionless granular materials. For simulation of the mechanical behaviour of a granular material during a monotonous deformation path, a hypoplastic constitutive model was used. To take into account a characteristic length of micro-structure, the constitutive model was extended by micro-polar terms. To take into account texturial effects, the granular hardness was modified. The calculations were carried out with a sand specimen during plane strain compression under constant lateral pressure. A stochastic and uniform distribution of the initial void ratio in the granular specimen was assumed. In addition, shear localization for two different uniform initial void ratios was investigated.
EN
The Zadnie Kamienne shear zone is a high-angle Riedel type shear zone (R'), exhibiting an antithetic sense of displacement, which may have developed synchronously with the nappe-thrusting of the Giewont Unit (High-Tatric Nappe). The amount of displacement along this zone is very low and does not explain the very intense deformation, which is of the same character as that at the base of the Giewont Unit (mylonitization, stylolitization and vein forming). The explanation of this phenomenon lies in the multiple activity of this zone, the change of the direction of movement and the important role of pressure solution in hydrothermal conditions responsible for dissolution creep, mass loss and stress relaxation. This kind of shear can be referred to as a "ravenous" shear zone. Neo-forming minerals accompanying these processes were applied as a temperature gauge. Simultaneous growth of albite and adularia indicates a temperature of about 350 degrees C. Chlorites accompanying them occur in two thermal episodes, the first of which indicating a similar temperature (292-357 C).
EN
Heterogeneity of granular materials triggers shear zone formation. In the paper, the FE-analysis of the effect of the material heterogeneity on the formation of a spontaneous shear zone inside of granular materials during a plane strain compression test is presented. The numerical calculations are performed with a finite element method on the basis of a hypoplastic constitutive law extended by polar quantities: rotations, curvatures and couple stresses. A mean grain diameter is used as a characteristic length. The constitutive law takes into account the effect of pressure, void ratio, direction of deformation rate and mean grain diameter on the behaviour of granular bodies. The heterogeneity in the granular body is assumed in the form of spots with a different initial void ratio. The spots are single or distributed randomly and stochastically with an exponential probability function. The single spots are distributed sparsely and densely in an initially dense and loose granular specimen. Special attention is focused on the effect of heterogeneity on the onset of shear localization and its thickness at residual state.
EN
The paper deals with numerical investigations on the patterning of shear zones in granular bodies. The behaviour of dry sand during plane strain compression tests was numerically modelled with a finite element method using a hypoplastic constitutive relation within a polar (Cosserat) continuum. The constitutive relation was obtained through an extension of a non-polar one by polar quantities, viz. rotations, curvatures, couple stresses using the mean grain diameter as a characteristic length. This relation can reproduce the essential features of granular bodies during shear localisation. The material constants can be easily determined from element test results and can be estimated from granulometric properties. The attention is laid on the influence of boundary conditions and the distribution of imperfections in the granular specimen on the formation of patterns of shear zones.
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