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International Concrete Abstracts Portal

Showing 1-5 of 738 Abstracts search results

Document: 

SP-343_37

Date: 

October 1, 2020

Author(s):

Berrocal, C.G.; Lundgren, K.; Löfgren, I.

Publication:

Symposium Papers

Volume:

343

Abstract:

In the present paper, long-term experiments involving natural corrosion of RC beams subjected to chloride solution cyclic exposure were carried out to investigate the effect of fibres on different aspects of the corrosion process as well as their contribution to the structural behaviour of RC elements damaged by corrosion. The long-term experiments were complemented with short-term accelerated corrosion experiments and mechanical tests to investigate the influence that low fibre contents may have on individual mechanisms that play an important role in the corrosion process of steel in concrete. These showed that fibres promote crack branching which results in a change of the internal crack pattern towards multiple thinner cracks, particularly near the reinforcement. This agrees with the long-term experiment results, which exhibited longer times to corrosion initiation for FRC beams with bending cracks and revealed a more distributed corrosion with more pits but less crosssectional loss compared to bars in plain concrete. Fibres also proved beneficial in delaying corrosion-induced cracks and preventing cover spalling, which greatly enhanced the bondbehaviour of corroded bars. Furthermore, a positive effect of the fibres was also observed on the residual flexural capacity of corroded beams, which generally increased the load-carrying capacity and rotation capacity.


Document: 

SP-343_11

Date: 

October 1, 2020

Author(s):

Ortiz-Navas, F.; Navarro-Gregori, J.; Serna Ros, P.; Leiva Herdocia, G.

Publication:

Symposium Papers

Volume:

343

Abstract:

In recent years, much research has shown improvements in shear behaviour and deformation capability when an adequate amount of macro fibres is provided in concrete. However, very few experiments have used macro synthetic fibres. In this paper, the shear capability of deformation in slender beams was studied by analysing the shear crack path, the crack openingslip relationship and shear deformation of polypropylene fibre-reinforced concrete (PFRC) beams. Shear cracks and deformations were measured by non-contact image measurement techniques. The results are compared with those of plain concrete (PC), steel fibre-reinforced concrete (SFRC) and reinforced concrete (RC) beams. Both types of fibres were dosed so that similar average residual tensile strengths would remain similar to one another. The crack path analysis results showed that synthetic fibres delayed the formation of shear cracks and their propagation into compression zone, and improved the behaviour of secondary cracks due to loss of bond with longitudinal reinforcement. Finally, the crack opening-slip relationship varied widely along the crack and location in beams.


Document: 

SP-343_45

Date: 

October 1, 2020

Author(s):

Look, K.; Mark, P.

Publication:

Symposium Papers

Volume:

343

Abstract:

An open design tool is developed that uses spreadsheet analyses, optimisation methods and iterative analytical routines. Its idea is to offer a universal, intuitive instrument to economically design and optimise steel fibre reinforced concrete members with or without rebar. The tool comprises non-linear evaluations of sectional forces with the yield line theory, a cross sectional design in ultimate and serviceability limit states as well as backward oriented optimisations of reinforcements, cross sectional properties or fibre classes. It should be free of specific code regulations and thus just basis on the assumption of plane strains, an ideal bond and requires the definitions of uniaxial stress-strain laws, strain boundaries and fundamental design formulas. Boundary conditions, material parameters and sectional properties as well as results like strain or stress distributions, performance ratios and potentials of improvements are given in visualisations and commented figures. The non-linear equations of equilibrium are iteratively solved with reduced gradient methods. Doing so, recursive initial parameter settings of the strain plane are – amongst other regularisations – incorporated to achieve robust solutions.


Document: 

SP-343_39

Date: 

October 1, 2020

Author(s):

Zanotti, C.; Randl, N.; Gar, P.S.; Far, B.K.; Steiner, M.

Publication:

Symposium Papers

Volume:

343

Abstract:

Fiber Reinforced Concrete (FRC) is being increasingly applied in structural repair and retrofit of reinforced concrete structures. Not only fiber reinforcement improves the durability of reinforced concrete structures, but it also enhances compatibility of the repair material to the existing structure, further enhancing structural effectiveness and service life of the intervention. Furthermore, studies have shown that fiber reinforcement can significantly improve substrate-repair bond in both tension and shear. However, this benefit is not fully utilized in repair/retrofit design due to test uncertainties and lack of comprehensive data on correlations with other fundamental factors. In this study, the question of the appropriateness, reliability and sensitivity of current bond tests in case of FRC repairs is addressed. Several tension and shear bond tests on plain and fiber reinforced cement-based repairs are performed in parallel by two research teams at UBC (Canada) and CUAS (Austria), following a rigorous testing procedure to allow consistency among results from the two laboratories. The influence of repair strength and casting direction is also investigated. The effect of fiber reinforcement on bond is assessed while correlation, comparability, and sensitivity of different test set-ups and stress conditions are discussed.


Document: 

SP-344_05

Date: 

October 1, 2020

Author(s):

Constantin E. Chalioris, and Chris G. Karayannis

Publication:

Symposium Papers

Volume:

344

Abstract:

Recently the use of special reinforcement arrangements has been extended in reinforced concrete members under torsion. These arrangements include (a) continuous rectangular spiral reinforcement, (b) epoxy bonded Carbon Fiber Reinforced Polymer (C-FRP) sheets as external transverse reinforcement and (c) short steel fibers as mass reinforcement. In this study an extended experimental program of 14 beams tested under torsion is presented. All specimens have the same geometrical characteristics but different transverse reinforcement arrangements. Six beams are used as pilot specimens; three of them have no transverse reinforcement and three have conventional steel stirrups. Further, two specimens have continuous steel spirals; four specimens have steel fibers as mass reinforcement and two specimens have externally bonded C-FRP sheets. The torsional behavior of these specimens is presented and compared to the behavior of the pilot specimens. Discussion and explanatory design examples about the application of these reinforcements are also included.


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