| 1. |
- Cairns, John, et al.
(författare)
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Bond of corroded reinforcement
- 2000
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Ingår i: Bond of reinforcement in concrete. - Lausanne : International Federation for Structural Concrete / Task Group Bond Models. - 2883940509 ; , s. 187-215
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Elfgren, Lennart, et al.
(författare)
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Anchor bolts and tension stiffening of rebars : two RILEM round robin investigations on bond
- 1998
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Ingår i: Fracture mechanics of concrete structures.. - : AEDIFICATIO Publishers. - 3931681238 ; , s. 1279-1290
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Konferensbidrag (refereegranskat)abstract
- Results from two RILEM Round Robin Investigations are presented. The first one deals with anchor bolts and the second one with bond and tension stiffening of rebars. Some 30 groups of researches encompassing over 70 people have performed more than 350 tests and analyses in America, Asia, Australia and Europe
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| 3. |
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| 4. |
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| 5. |
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| 6. |
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| 7. |
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| 8. |
- Engström, Björn, et al.
(författare)
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Anchorage and bond in high strenght concrete
- 2000
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Ingår i: Bond of reinforcement in concrete. - Lausanne : International Federation for Structural Concrete / Task Group Bond Models. - 2883940509 ; , s. 99-156
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Gambarova, Pietro, et al.
(författare)
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Bond mechanics including pull-out and splitting failures
- 2000
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Ingår i: Bond of reinforcement in concrete. - Lausanne : International Federation for Structural Concrete / Task Group Bond Models. - 2883940509 ; , s. 1-98
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Groth, Patrik, et al.
(författare)
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Fiberarmerad betong
- 1996
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Ingår i: Byggforskning : Byggforskningsrådets tidning för en bättre byggd miljö. - 1102-3686. ; :3, s. 41-
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 11. |
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| 12. |
- Noghabai, Keivan
(författare)
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Beams of fibrous concrete in shear and bending: experiment and model
- 2000
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Ingår i: Journal of Structural Engineering. - 0733-9445 .- 1943-541X. ; 126:2, s. 243-251
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Tidskriftsartikel (refereegranskat)abstract
- Beams of high-strength concrete (fcc up to 90 MPa) were tested in shear and bending. Various types of fiber (metallic and nonmetallic) were added to the concrete matrix to up to 1% per volume concrete. Also, four different beam depths were investigated. The efficiency of fibers depends on the governing load-carrying mechanisms, which may vary for different beam dimensions. The chosen steel fibers did not improve the capacity of the 250 mm deep beams as they did not for some of the 300 mm beams. They enhanced the toughness in the 500 mm beams, but were not enough for the 700 mm beams. Also, a fiber cocktail may prove more effective than using a single type of fiber. The chosen steel fibers are competitive with conventional stirrups, according to this study. A nonlinear truss model is devised to predict the load-carrying capacity of the beams. The model gave good predictions for beams without stirrups and depths up to 500 mm
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| 13. |
- Noghabai, Keivan
(författare)
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Behavior of tie elements of plain and fibrous concrete and varying cross sections
- 2000
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Ingår i: ACI Structural Journal. - : American Concrete Institute. - 0889-3241 .- 1944-7361. ; 97:2, s. 277-284
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Tidskriftsartikel (refereegranskat)abstract
- The tension stiffening effect on reinforcing bars embedded in concrete prisms is investigated experimentally. Both metallic (steel) and non-metallic (polyolefin and carbon) fibers of different dimensions are used in high-strength concrete mixtures. In addition, the cross section is varied. The softening behavior of the concrete, determined through a uniaxial tension procedure, was used in an analytical model. The model reproduced the dependency of the load-deformation responses of the elements on the tensile behavior of the concrete
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| 14. |
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| 15. |
- Noghabai, Keivan
(författare)
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Bond of deformed bars in concrete
- 1996
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Ingår i: Proceedings. - Oslo : Norsk Betongforening. - 8291341028 ; , s. 155-156
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Konferensbidrag (refereegranskat)
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| 16. |
- Noghabai, Keivan, et al.
(författare)
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Bond properties of high-strength concrete
- 1993
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Ingår i: Utilization of High Strength Concrete : Proceedings. - Oslo : Norsk Betongforening. - 8291341001 ; , s. 1169-1176, s. 263-265
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Konferensbidrag (refereegranskat)
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| 17. |
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| 18. |
- Noghabai, Keivan
(författare)
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Cracked RC elements subjected to simultaneous loading and frost cycles
- 2001
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Ingår i: Concrete under severe conditions. - Vancouver : University of British Columbia, Dept. of Civil Engineering. - 888657900 ; , s. 1050-1057
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Konferensbidrag (refereegranskat)abstract
- Precracked reinforced concrete elements were subjected to sustained tensile loading while having one face covered by salt solution and exposed to frost cycles according to the Swedish Standard SS 137244 (Boras method). The test went on for 56 days. The variables in the experiment were the concrete composition, the cover thickness, and load levels. The cracks influenced the scaling apart from exposing the interior of the element to chlorides, and more so for porous concrete. The problem is highly related to the actual testing conditions, which have to be carefully monitored.
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| 19. |
- Noghabai, Keivan
(författare)
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Discrete versus smeared versus element-embedded crack models on ring problem
- 1999
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Ingår i: Journal of engineering mechanics. - 0733-9399 .- 1943-7889. ; 125:3, s. 307-314
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Tidskriftsartikel (refereegranskat)abstract
- Three different concepts in finite-element modeling are compared by analyzing a thick-walled concrete ring subjected to an internal pressure. These are the discrete crack, the fixed smeared crack, and an element-embedded crack model called the inner softening band (ISB) model. The results are compared with experimental studies on rings of both normal- and high-strength concrete mixtures with and without spiral reinforcement. The ISB analysis gives the best results with respect to explaining the fracture mechanism as well as consistency in prediction of the ring capacity. The smeared crack model also provides satisfactory results, but in the light of robustness in geometrical modeling and requirement of minimum amount of input data (which all have a physical relevance) the ISB concept in this case is more reliable. The study exposed some deficiencies of the discrete crack method based on the fact that the localization processes and the strain redistribution in the body are often unknown. This also underlines caution in assuming symmetry when softening occurs on a structural level
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| 20. |
- Noghabai, Keivan, et al.
(författare)
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Effect of tension softening of concrete on the tension stiffening of rebars in plain and fibrous concrete
- 1998
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Ingår i: Fracture mechanics of concrete structures. - : AEDIFICATIO Publishers. - 3931681246 ; , s. 1547-1556
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Konferensbidrag (refereegranskat)abstract
- Tension stiffening effect on rebars embedded in concrete prisms are investigated through computational as well as analytical methods and compared with experimental results. Both metallic (steel) and non-metallic (polyolefin and carbon) fibres of different dimensions are used in high-strength concrete. The softening behaviour of concrete determined by a uniaxial tensile procedure, was used in FEM and analytical models. The tension stiffening effect may be more dependent on the tensile behaviour of the concrete than on a relative slip between rebar and concrete
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| 21. |
- Noghabai, Keivan
(författare)
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Effect of tension softening on the performance of concrete structures : experimental, analytical and computational studies
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The tensile characteristics of concrete are usually neglected in the design of structures. The treatise discusses the important bearing these very characteristics have on the performance of different concrete structures. The investigations are supported by experiments, theoretical models and simulations by finite element methods. The following structures are studied: thick-walled concrete rings subjected to inner pressure, tensioned rebars embedded in concrete prisms and fullscale reinforced concrete beams under flexural loading. A hierarchic approach is adopted meaning that for the analysis of the beams, the results of the reinforced concrete prisms are used as constitutive law. In turn, for modelling the behaviour of the prism, the characteristics of the rebar and concrete are used as input. Being based on a mechanical foundation rather than empirical, this approach enables to consider how the behaviour of a structure will alter if its constituents are e g exposed to environmental effects. It offers great prospect for development of new materials and guidelines for design of durable reinforced concrete structures.
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| 22. |
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| 23. |
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| 24. |
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| 25. |
- Noghabai, Keivan
(författare)
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FE-modelling of cover splitting due to corrosion by use of inner softening band
- 1999
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Ingår i: Materials and Structures. - 1359-5997 .- 1871-6873. ; 32:7, s. 486-491
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Tidskriftsartikel (refereegranskat)abstract
- The splitting of concrete covers due to the expansive action of corrosion has been investigated by a finite element method (FEM) based on an element-embedded crack concept called the inner softening band. Fictive cross-sections, with and without transverse reinforcement, were studied. The concrete composition (plain and fibrous high-strength concrete) and the cover thickness were varied. The model produced credible fracturing behaviour in concrete covers and explained the mechanical origin of the cracks. For cover thicknesses less than two times the bar diameter, fibres do not seem to have any significant effect on occurrence of splitting cracks. However, fibres are effective to arrest the opening of arisen splitting cracks and to redistribute the strains to other cracks. Hence, fibres may postpone or prevent a total spalling of concrete covers. A larger cover is necessary not only to prolong the initiation period, but also for the fibres (2 volume-%) to be effective beyond occurrence of corrosion induced cover cracks.
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| 26. |
- Noghabai, Keivan, et al.
(författare)
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Fibre reinforced high strength concrete beams in shear
- 1999
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Ingår i: High strength concrete : first international conference. - : American Society of Civil Engineers (ASCE). - 0784404194 ; , s. 480-193
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Konferensbidrag (refereegranskat)
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| 27. |
- Noghabai, Keivan, et al.
(författare)
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Fracture mechanics applied to bond
- 1997
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Ingår i: Advanced design of concrete structures. - Barcelona : International Center for Numerical Methods in Engineering (CIMNE). - 8487867944 ; , s. 57-64
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Konferensbidrag (refereegranskat)
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| 28. |
- Noghabai, Keivan, et al.
(författare)
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Load carrying capacity of beams using fibres as shear reinforcement
- 1998
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Ingår i: Fracture mechanics of concrete structures. - : AEDIFICATIO Publishers. - 3931681246 ; , s. 1491-1500
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Konferensbidrag (refereegranskat)abstract
- The load bearing capacity of reinforced beams of fibrous high- strength concrete is investigated, experimentally and computationally. Both metallic (steel) and non-metallic (polyolefin and carbon) fibres are used, keeping the volume fraction to 1%. A nonlinear truss model is outlined which incorporates most of the pertinent mechanisms in the experiments, including the rebar-to-concrete bond and crack widths. The law for evolution of stable growth of local cracks in the structure is based on the response of uniaxial tensile tes
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| 29. |
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| 30. |
- Noghabai, Keivan
(författare)
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Reinforced concrete elements under combined loading and environmental exposure: survey on degradation processes and experimental study
- 2001
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The simultaneous effect of mechanical loading and exposure to aggressive environment was studied on reinforced concrete (RC) elements. The elements comprised a single reinforcing 16 mm bar (Swedish Grade Ks500) embedded in 640 mm long concrete prisms with square cross-sections. The cover thicknesses were set to 2 and 3 times the bar diameter. The elements were precracked to control the spacing and widths of tensile cracks as well as to reduce the influence of time-dependent effects of creep and rate of loading. During the entire test the elements were loaded to either of two load levels (around 25 kN and 45 kN) giving average crack widths of approximately 0.05 mm and 0.15 mm for the respective load level. The cracks expose the interior of the elements to the aggressive environment. Here the environmental attack was created by covering an exposed cracked surface by a 3% sodium chloride solution that was allowed to freeze and thaw during one day, with the temperature varying between +20°C and -20°C. The exposure test went on for 56 days in accordance to the Swedish Standard SS 13 72 44, so-called Borås method. Tests were also performed on 150x150x50 mm slabs. In all cases the top faces were exposed. From durability aspect, the concrete tightness and porous system are decisive. Two different concrete mixtures were used: Concrete (A) and (B) with water-to-cement ratios 0.70 and 0.45. All together, 12 RC elements were tested. Based on the amount of scaling on slabs, concrete (A) had a poor frost resistance, whereas concrete (B) had a good (or even excellent) resistance. Despite the marked differences in durability between the two concretes, they had quite similar mechanical properties, both in compression and in tension. The observed differences between scaling in RC elements and slabs were more conspicuous for concrete (A), implying that cracks are more detrimental for a poorer concrete. The rate of scaling increases also in areas that are under local high stresses, and when the element is being bent. After 56 days exposure, higher concentrations of chlorides were found in the concrete at the location of the reinforcing bar for a larger crack (approximately 0.15 mm) than in a smaller crack (approximately 0.05 mm). For longer period of exposure the chloride concentration may even out. This does not necessarily mean that the service life of the structure is expired, even if corrosion processes have initiated at the location of a crack. Consequently, better criteria for assessment of service life of cracked RC structures are needed. The experiments have shown a great complexity with respect to both physical degradation of concrete (due to frost cycles and transport mechanisms in the concrete) and the experimental conditions (in terms of loading and the temperature variations in the climate chamber). This study thus serves as a step to further illuminate the problems to be faced when trying to correctly characterise actual conditions in field.
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| 31. |
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| 32. |
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| 33. |
- Olofsson, Thomas, et al.
(författare)
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Anchorage and bond properties in concrete
- 1995
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Ingår i: Fracture of brittle, disordered materials. - London : Taylor and Francis Group. - 0419190503 ; , s. 525-543
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Konferensbidrag (refereegranskat)
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| 34. |
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| 35. |
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| 36. |
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Tension of reinforced concrete prisms : round robin analysis and tests on bond : a report from an investigation arranged by RILEM technical committee 147-FMB fracture mechanics to anchorage and bond
- 2001
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- Results are presented from a RILEM Round Robin Investigation. It deals with tension stiffening of reinforcement bars embedded in concrete tie elements. Seven groups of researches have performed some 50 tests and analyses. Parameters discussed are: cover thickness, crack spacing, bar size, tension stiffening of naked reinforcing bars, and influence of concrete strain softening. Similar trends were seen in the different tests and most of the applied theoretical models give reasonable results. The general behaviour is similar, although there seems to be some differences between the tested cracking loads. The models used are able to predict the bond behaviour in a correct way: analytical models based on the tension softening of concrete; bond-slip relations; as well as finite element methods with inner softening bands. The CEB-FIP Model Code can be used for design purposes and gives straight-forward predictions. The following new and/or refined insights were obtained from the tests: Cover thickness and crack spacing. - The number and spacing of visible cracks are more or less proportional to the thickness of the concrete cover. Bar diameter size effect. - There is a small tendency to a proportionally lower tension stiffening effect for larger bar sizes but the scatter is too large to secure definite conclusions. Longitudinal splitting and yielding of reinforcement. - Longitudinal splitting cracks occurred close to and after yielding of the reinforcement. Tension stiffening of naked reinforcing bars. - A new hypothesis of a tension stiffening of the bare reinforcing bar has been presented. Concrete strength and strain softening - The crack opening resistance is given by the tension softening curve of the concrete. By addition of fibres to the concrete matrix, the curve is changed, and the crack opening resistance is improved without necessarily changing other properties of the concrete. The chosen amount and type of fibers do not necessarily have much influence on the tensile strength, and the same crack patterns will be obtained on elements with the same geometry. The shape of the load-deformation curve, however, is considerably changed compared to that of the plain concrete. This is due to the enhanced crack-opening resistance, whereas the stiffening effect seems to depend on the crack spacing and consequently on the cover thickness and the degree of confinement it provides.
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