Abstract
Strengthening of concrete beams with externally bonded fibre-reinforced plastic (FRP) materials appears to be a feasible way of increasing the load-carrying capacity and stiffness characteristics of existing structures. FRP-strengthened concrete beams can fail in several ways when loaded in bending. The following collapse mechanisms are identified and analysed in this study: steel yield-FRP rupture, steel yield-concrete crushing, compressive failure, and debonding. Here we obtain equations describing each failure mechanism using the strain compatibility method, concepts of fracture mechanics and a simple model for the FRP peeling-off debonding mechanism due to the development of shear cracks. We then produce diagrams showing the beam designs for which each failure mechanism is dominant, examine the effect of FRP sheets on the ductility and stiffness of strengthened components, and give results of four-point bending tests confirming our analysis. The analytical results obtained can be used in establishing an FRP selection procedure for external strengthening of reinforced concrete members with lightweight and durable materials.
Resume
Le renforcement externe de poutres de béton par collage de plastiques renforcés de fibres (FRP) semble un moyen adéquat d'accroître la capacité portante et la rigidité des constructions existantes. Les poutres de béton renforcées de FRP peuvent se rompre de différentes manières quand elles sont chargées en flexion. On identifie et on analyse dans cette étude les processus d'effondrement: fléchissement acier-rupture FRP, fléchissement acier-fragmentation du béton, rupture en compression et décollement.
Nous obtenons ici des équations décrivant chaque mécanisme de rupture en ayant recours à la méthode de déformation compatible, aux concepts de la mécanique de la rupture et à un modèle simple pour le mécanisme du décollement dû aux fissures de cisaillement. Ensuite, nous produisons des diagrammes montrant les calculs de poutre correspondant à chaque mécanisme de rupture, et nous examinons les effets des feuilles de FRP sur les caractéristiques de ductilité et de rigidité des composants renforcés.
En fin de compte, nous donnons les résultats d'essais de flexion quatre points sur des poutres en béton armé renforcées de diverses quantités de feuilles de carbone FRP unidirectionnelles (CFRP). Les résultats confirment l'analyse et soulignent le rôle important de la fissuration dans la délamination de la plaque composite par le processus de décollement. Il apparaît que ce processus impose une limite à l'épaisseur de la feuille composite au-delà de laquelle une rupture fragile se produit, sans que la capacité de flexion soit entièrement réalisée ni la ductilité assurée. On peut utiliser les résultats analytiques obtenus pour établir un processus de sélection de FRP pour le renforcement externe d'éléments de béton par des matériaux légers et durables.
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Abbreviations
- A :
-
Area
- A s :
-
Area of steel reinforcement
- a :
-
Crack length
- b :
-
Width of cross-section
- b fc :
-
Width of fibre-composite sheet
- C :
-
Compliance
- c :
-
Distance from extreme compressive fibre to neutral axis
- d :
-
Effective depth
- E :
-
Young's modulus
- E c :
-
Young's modulus of concrete
- E fc :
-
Young's modulus of fibre-composite
- E s :
-
Young's modulus of steel
- f c :
-
Stress in concrete
- f′c :
-
Compressive strength of concrete
- f fc :
-
Stress in fibre-composite
- f r :
-
Modulus of rupture for concrete
- f s :
-
Stress in steel
- f y :
-
Yield stress of steel
- G :
-
Shear modulus
- G fc :
-
Shear modulus of fibre-composite
- G s :
-
Shear modulus of steel
- G II :
-
Mode II strain energy release rate
- G IIC :
-
Critical mode II strain energy release rate
- h :
-
Height of cross-section
- I :
-
Moment of inertia
- k :
-
Constant
- M :
-
Bending moment
- M cr :
-
Bending moment at first cracking
- M u :
-
Ultimate bending moment
- M y :
-
Bending moment at first yield
- P :
-
Load
- t :
-
Thickness of fibre-composite
- U :
-
Strain energy
- u :
-
Displacement
- V :
-
Shear force
- v :
-
Vertical crack opening displacement
- w :
-
Horizontal crack opening displacement
- \(\bar y\) :
-
Depth of centroid of the concrete stress block
- β 1 :
-
Constant used to define the depth of the equivalent rectangular stress block
- ε c :
-
Strain in concrete
- ε tc :
-
Strain at concrete top fibre
- ε fc :
-
Strain in fibre-composite
- ε *fc :
-
Initial strain at extreme tensile fibre of concrete
- ε s :
-
Strain in steel
- λ:
-
Constant
- ρ fc :
-
Area fraction of fibre-composite
- ρ lfc :
-
Lower limit of fibre-composite
- ρ ufc :
-
Upper limit of fibre-composite area fraction
- ρ s :
-
Area fraction of steel reinforcement
- ϕ:
-
Curvature
- φ cr :
-
Curvature at first cracking
- φ u :
-
Ultimate curvature
- φ y :
-
Curvature at first yield
References
Fleming, C. J. and King, G. E. M., ‘The development of structural adhesives for three original uses in South Africa’ in Proceedings of RILEM International Symposium on Synthetic Resins in Building Construction, Paris 1967, pp. 75–92.
Irwin, C. A. K., ‘The Strengthening of Concrete Beams by Bonded Steel Plates’, TRRL Supplementary Report 160 UC (Transport and Road Research Laboratory, Department of the Environment, Crowthorne, UK, 1975, p. 8.
Hugenschmidt, H., “Epoxy adhesive for concrete and steel’, in Proceedings of 1st International Congress on Polymers in Concrete, London, 1976, pp. 195–209.
Dussek, I. J., ‘Strengthening of Bridge Beams and Similar Structures by Means of Epoxy-Resin-Bonded External Reinforcement’, Transportation Research Record No. 785 (1980) pp. 21–24.
Ryback, M., ‘Reinforcement of bridges by gluing of reinforcing steel.’Mater. Struct. 16(91) (1981) 13–17.
Van Gemert, D. A., ‘Repairing of concrete structures by externally bonded steel plates’, in Proceedings of ICP/RILEM/IBK International Symposium on Plastics in Material and Structural Engineering, Prague, 1982, pp. 519–526.
Klaiber, F. W., Dunker, K. F., Wipf, T. J. and Sanders, W. W., Jr, ‘Methods of Strengthening Existing Highway Bridges’, Transportation Research Board NCHRP Report (1987) 293.
Swamy, R. N., Jones, R. and Bloxham, J. W., ‘Structural behaviour of reinforced concrete beams strengthened by epoxy-bonded steel plates,’Struct. Engnr 65A(2) (1987) 59–68.
Ranisch, E. H. and Rostasy, F. S., ‘Bonded steel plates for the reduction of fatigue stresses of coupled tendons in multispan bridges’, in ‘Adhesion Between Polymers and Concrete’, RILEM ISAP 86 (1986) pp. 561–570.
Meier, U., ‘Bridge repair with high performance composite materials,’Mater. Technik 4 (1987) 125–128.
Saadatmanesh, H. and Ehsani, M., ‘Application of fibercomposites in civil engineering’, in Proceedings of the sessions related to structural materials at Structures Congress '89, ASCE (1989) pp. 526–535.
Kaiser, H., ‘Strengthening of Reinforced Concrete with Epoxy-Bonded Carbon-Fiber Plastics,’ doctoral thesis, ETH, Zurich (1989).
L'Hermite, R. and Bresson J., ‘Concrete reinforced with glued plates’, in Proceedings of RILEM International Symposium on Synthetic Resins in Building Construction, Paris, 1967, pp. 175–203.
Lerchenthal, C. H., ‘Bonded steel reinforcement for concrete slabs’,ibid. Proceedings of RILEM International Symposium on Synthetic Resins in Building Construction, Paris, 1967, pp. 165–173.
MacDonald, M. D., ‘The Flexural Behaviour of Concrete Beams with Bonded External Reinforcement,’ TRRL Supplementary Report 415, Transport and Road Research Laboratory, Department of the Environment, Crowthorne, UK, 1978, p. 13.
Jones, R., Swamy, R. N., Bloxham, J. and Bouderbalah, A., ‘Composite behaviour of concrete beams with epoxy bonded external reinforcement,’Int. J. Cement Compos. Lightwt Concr. 2(2) (1980) 91–107.
Jones, R., Swamy, R. N. and Ang, T. H., ‘Under- and over-reinforced concrete beams with glued steel plates’4(1) (1982) 19–32.
Ladner, M., ‘Reinforced concrete members with subsequently bonded steel sheets’, in Proceedings of IABSE Symposium on Strengthening of Building Structures— Diagnosis and Therapy, Venezia, Final Report, Vol. 46 (1983) pp. 203–210.
Kent, D. C. and Park, R., ‘Flexural members with confined concrete’,J. Struct. Div. ASCE 97(7)(1971) 1969–1990.
Knott, J. F., ‘Fundamentals of Fracture Mechanics’ (Butterworths, London, 1973).
Anandarajah, A. and Vardy, A. E., ‘A theoretical investigation of the failure of open sandwich beams due to interfacial shear fracture’,Struct. Engr 63B(4) (1985) 85–92.
Triantafillou, T. C. and Gibson, L. J., ‘Debonding in foam-core sandwich panels’,Mater. Struct. 22 (1989) 64–69.
Hamoush, S. A. and Ahmad, S. H., ‘Debonding of steel plate-strengthened concrete beams’,J. Struct. Engng ASCE 116(2) (1990) 356–371.
Ladner, M. and Weder, C., ‘Concrete Structures with Bonded External Reinforcement’, EMPA Report No. 705 (1981).
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Triantafillou, T.C., Plevris, N. Strengthening of RC beams with epoxy-bonded fibre-composite materials. Materials and Structures 25, 201–211 (1992). https://doi.org/10.1007/BF02473064
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DOI: https://doi.org/10.1007/BF02473064