| 1. |
- Fall, David, 1983, et al.
(författare)
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Modelling cracking and bending failure of SFRC beams with conventional reinforcement
- 2013
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Ingår i: 8th International Conference on Fracture Mechanics of Concrete and Concrete Structures. - 9788494100413 ; , s. 1276-1285
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Konferensbidrag (refereegranskat)abstract
- In this study three beams, with varying contents of steel fibre reinforcement, were tested in four point bending and compared with results from FE-analysis. The beams were part of a larger experimental programme where relevant material properties were investigated. FE-modelling was performed using a two dimensional model. Concrete was represented by four-node quadrilateral isoperimetric plane stress elements. The smeared crack approach was utilized and the stress-strain relation describing the tensile behavior of the concrete was calculated from uni-axial test results, assuming the crack bandwidth to be equal to the element length. In compression, the concrete was assumed to behave elasto ideal-plastic. The reinforcement was modelled by straight 2-node truss elements connected to the concrete by two-dimensional interface elements providing the bond-slip properties. A material model including hardening effects was derived from tension tests of reinforcement bars and used for modelling the conventional reinforcement. A multi-linear bond-slip model was established through pull-out tests. As an alternative, analyses were also performed taking into account a reduction of the bond stress after yielding of the reinforcement occurred. Loading was applied in two phases: the first comprehending only the self-weight, while incremental loading was applied by deformation control during the second phase. General agreement between experiments and FE-analyses was obtained with regard to load-displacement behaviour. By observing the crack patterns, both from FE-analysis and experiments, it can be concluded that the general behaviour agreed; however, in the analyses not all cracks were fully localized. A higher degree of crack localization was obtained when the bond loss at yielding was included.
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| 2. |
- Fall, David, 1983, et al.
(författare)
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Non-linear Finite Element Analysis of Steel Fibre Reinforced Beams with Conventional Reinforcement
- 2012
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Ingår i: 8th RILEM International Symposium on Fiber Reinforced Concrete: challenges and opportunities (BEFIB 2012). - 9782351581322 ; , s. 1033-1045
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Konferensbidrag (refereegranskat)abstract
- The purpose of this study has been to investigate the behavior of elements reinforced with both conventional steel reinforcement and steel fibres in order to support future applications of such composites. Three beams of varying fibre content were tested in four-point bending. The results were then compared with results from nonlinear FE-analyses and the calculation method suggested in fib Model Code 2010. The beams were a part of a larger experimental programme where relevant properties were investigated in uniaxial tension tests and pull-out tests. The FE-modeling was performed using a two dimensional plane stress model. General agreement between experiments and the FE-analyses was obtained with regard to load-displacement behavior. The crack patterns from the FE-analysis and experiments agreed in general, although the crack patterns in the analysis were more distributed close to the reinforcement. Crack localization was enhanced by modifying the bond-slip behavior to include the bond loss at yielding. Calculations in accordance with fib Model Code 2010 yield conservative results in comparison with both experiments and FE-analysis.
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| 3. |
- Jansson, Anette M, 1963
(författare)
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Analysis and design methods for fibre reinforced concrete: a state-of-the-art report
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- During the past decades the concrete construction field has experienced a growing interest in the advantages fibre reinforcement has to offer. Of the different fibres available, e.g. steel, synthetic and glass fibres, the steel fibre is the most investigated and most commonly used. Fibre reinforcement today is mainly used in applications such as sprayed concrete, industrial floors and overlays, although other application areas exist. Some of the potential benefits from the adding of fibres to concrete are improved crack control and more slender constructions. The extent of the crack control depends on the amount of fibres added, and plays a great role for durability. As of today there exist no generally accepted design- and analysis procedures, and if the technique with fibres is to move forward, there is a need for development of such methods. Several technical committees have proposed design methods based on a stress-strain relationship, but also methods based on a stress-crack width relationship are proposed. Different methods for analysis of fibre reinforced concrete structural members are also proposed by several researchers. Comparison and evaluation of these methods, will provide a base for further research aiming at improvement of the, at the moment, available methods. It is found that for design, the Italian proposal provides a comprehensive method taking a step in the right direction considering the different ways of determining the characteristic length (for translating crack-width into strain). An improvement though, would be if the formula for calculation of crack width/crack spacing were to be modified according to a proposal made by Löfgren, see Gustafsson and Karlsson (2006). Regarding analysis, all the reviewed methods yield good results in comparison with experiments described in the reviewed articles.
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| 4. |
- Jansson, Anette M, 1963, et al.
(författare)
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Applying a fracture mechanics approach on FRC beams, material testing and structural analysis
- 2008
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Ingår i: Submitted to Journal of Advanced Concrete Technology.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The presented work has been focused on strain-softening FRC and the interrelationship between material properties and structural behaviour. The main purpose of this work was to establish a procedure for structural analysis of flexural members with a combination of steel fibres and conventional reinforcement. A systematic approach for material testing and structural analysis, based on fracture mechanics, has been used and this covers: (1) material testing; (2) inverse analysis; (3) adjustment of the -w relationship for fibre efficiency; and (4) cross-sectional and structural analysis. The results suggest that the approach used for the material testing provides the necessary properties to perform analyses based on non-linear fracture mechanics. The structural behaviour could be predicted with good agreement with FEM using both bi-linear and multi-linear -w relationships. When comparing the peak loads obtained in the experiments with the results from the analyses, the agreement was good, with a high correlation. This demonstrates the strength of the fracture-mechanics approach for material testing and structural analysis.
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| 5. |
- Jansson, Anette M, 1963, et al.
(författare)
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Applying a fracture mechanics approach to material testing and structural analysis of FRC beams
- 2007
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Ingår i: Conference proceedings for FRAMCOS-6, Catania, Italy June 2007. ; , s. 1491-1496
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Konferensbidrag (refereegranskat)abstract
- The presented work has been focused on strain-softening FRC and the interrelationship between material properties and structural behaviour. The main purpose of this work was to establish a procedure for structural analysis of flexural members with a combination of conventional reinforcement and steel fibres. A systematic approach for material testing and structural analysis, based on fracture mechanics has been used, this covers: (1) material testing; (2) inverse analysis; (3) adjustment of the -w relationship for fibre efficiency; and (4) cross-sectional and structural analysis. The results suggest that the approach used for the material testing provides the necessary properties to perform analyses based on non-linear fracture mechanics. The structural behaviour could be predicted with good agreement, using both FEM and an analytical model, and when comparing the peak loads obtained in the experiments with the results from the analyses, the agreement was good, with a high correlation. Hence, this demonstrates the strength of the fracture-mechanical approach for material testing and structural analysis.
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| 6. |
- Jansson, Anette M, 1963, et al.
(författare)
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Bond between Reinforcement and Self-Compacting Steel-Fibre-Reinforced Concrete
- 2012
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Ingår i: Proceeding of the Fourth International Conference on Bond in Concrete 2012: Bond, Anchorage, Detailing. ; 1, s. 323-329
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Konferensbidrag (refereegranskat)abstract
- In this study, pull-out tests of specimens with short embedment length and varying fibre content were carried out. The results showed no effect from the fibres on the bond-slip behaviour before peak load when normalized with respect to the compressive strength. After peak, the fibre reinforcement provided extra confinement, changing the failure mode from splitting to pull-out failure. The test results were used to calibrate a frictional bond model in non-linear finite element analyses. The model proved to yield results in good agreement with the experimental results regarding failure modes, load-slip relation and splitting strains on the surfaces of the pull-out specimens. The tests and analyses in combination confirmed that the fibre reinforcement neither disturbed nor improved the bond properties at the interface layer between reinforcement steel and concrete; i.e. the fibres only provided confinement to the surrounding structure.
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| 7. |
- Jansson, Anette M, 1963, et al.
(författare)
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Bond of reinforcement in self-compacting steel-fibre-reinforced concrete
- 2012
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Ingår i: Magazine of Concrete Research. - : Thomas Telford Ltd.. - 0024-9831 .- 1751-763X. ; 64:7, s. 617-630
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Tidskriftsartikel (refereegranskat)abstract
- Crack control, one of the main benefits of using fibre reinforcement, depends to a large extent on the concrete-rebar bond. Pull-out tests of specimens with short embedment length were carried out and the results showed no effect from the fibres on the normalised bond-slip behaviour before peak load. After this, the fibre reinforcement provided extra confinement, changing the failure mode from splitting to pull-out failure. The test results were used to calibrate a finite-element bond model that considers both tangential stresses and stresses in the radial direction from the rebar. Splitting cracks may be thus considered in the finite-element analyses. The model proved to yield results in good agreement with the experimental results regarding failure mode, load-slip relation and splitting strains on the surfaces of the pull-out specimens. The analyses revealed that two types of action were active in the cracking process. In addition, the confinement effect of the fibre reinforcement was compared with the confinement of conventional stirrups using the bond model in CEB-FIP model code 2010.
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| 8. |
- Jansson, Anette M, 1963, et al.
(författare)
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Design methods of fibre reinforced concrete: a state-of-the-art review
- 2008
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Ingår i: Submitted to Nordic Concrete Research.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The increasing interest in the use of fibre reinforcement has created a need for established design and analysis methods. Fibre reinforcement is mainly used in applications such as industrial floors and sprayed concrete, although other application areas exist. Apart from increased load carrying capacity, one of the main benefits of adding fibres to concrete is the potential reduction in crack width, which depends on the amount of fibres added and positively affects the durability of the finished structure. By comparing ten design methods proposed by technical committees, this paper provides a basis for further research aimed at developing a common design basis. Evaluation is based on the way the fibre capacity is considered. In addition, a “good” design method should also consider all (or most) design situations. It was found that, for design, the Italian proposal provides comprehensiveness. However, some amendments are needed, e.g. a suggestion is that the proposed formula for calculating crack width/crack spacing be modified to also consider the residual tensile strength.
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| 9. |
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| 10. |
- Jansson, Anette M, 1963
(författare)
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Effects of Steel Fibres on Cracking in Reinforced Concrete
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- ABSTRACTAlthough it is well known that fibre reinforcement acts as a crack arresting agent, there is still a need for deeper knowledge of the actual cracking behaviour, especially regarding cracks with widths smaller than 0.3mm. Today major fibre applications are as a replacement for the welded mesh in industrial floors, and as reinforcement in sprayed concrete. However, other applications exist and are investigated.By combining experiments with finite-element analyses, the effects of fibres on cracking in conventionally reinforced, self-compacting, steel-fibre-reinforced concrete (SCSFRC) were studied. When studying the beginning of the cracking process, the tensile softening behaviour (-w relationship), and the bond stress-slip behaviour, which are the ones mainly affecting the cracking, are clearly of interest. Contradictory information on the effect of fibres on bond behaviour was found in the literature. Pull-out tests with short embedment length were thus carried out. The -w relationship may be obtained indirectly by inverse analysis, e.g. from wedge-splitting tests, or directly, from uniaxial tension tests (UTT); both approaches were used in this work. To investigate the cracking process, tension tests of tie elements were carried out, where, in addition to the load-deformation curves, a full-field strain measuring technique using Digital Image Correlation (DIC) was used to monitor the surface cracking.It was found from the pull-out tests that, for the type and amount of fibres used here, the bond properties at the interface layer were neither reduced nor improved. There were indications, however, that the initial stiffness of the bond stress-slip curves was increased by the self-compacting concrete. The UTT and the tie element testing showed that the scatter was quite high regarding the number of fibres in a cut cross section. It was seen that fibre reinforcement markedly improves tension stiffening and, at a given load, the characteristic crack width is greatly reduced compared with plain concrete. The DIC gave good insight into the surface crack initiation and enabled the tension stiffening to be quantified by relating it to the characteristic crack widths. In addition, it was seen that the cracking load and first-peak tensile stress increased with an increasing amount of fibres.The Finite element analyses of the beams and the tie elements revealed that the methodology used was versatile. It was found that the smeared crack model did not yield crack localization for materials with high fibre content (Vf > 0.5%) if homogenous material properties were assumed. Instead a semi-meso approach was used; properties for plain concrete were assigned to randomly designated parts of the elements, while the remaining elements were assigned modified tensile properties. The modified properties were increased so that the average -w curve of one cross section corresponded to the average curve from the UTT. With the new approach, the load-elongation response agreed better with the experiments; crack localization was obtained and crack widths could be reasonably reproduced.
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