Keywords: composites, adhesives, bonding, damage, concrete, repairing.

Fibre reinforced composites are increasingly becoming important in the construction industry because of their advantageous properties not available from other materials. It is of special interest and widespread acceptance the bonding of fibre-reinforced plastic (FRP) plates to critical areas on the concrete structures (bridge beams and slabs) which are under tension as an excellent method of strengthening and retrofitting of existing structures [1]. The advantage of this technique is that the work can be carried out while the structure is still in use.

Many authors have investigated the fundamental mechanical properties of FRP products developed for use as reinforcement for concrete. Such properties were found to be generally acceptable from laboratory tests for its application as structural reinforcement in buildings and bridges.

However, the application of this technique can produce some difficulties due to the brittle nature of the local failure mode of the strengthened beam produced by the debonding of the composite plate and the beam [2]. The abrupt termination of the plate can result in a strong concentration of shear and vertical normal stresses which cause the plate to peel off towards the centre of the beam [3]. The debonding occurs suddenly and in a brittle manner. Therefore, the failure behavior in plated concrete beams is strongly dependent on the succesful transmission of bond stresses between the plates and the beam via the adjacent connecting layers of the FRP plate, adhesive and cover concrete.

Then, a good simulation of the stresses at the concrete/FRP interface is an important issue since in many cases the failure of retrofitted beams is governed by this kind of "local failure". In the numerical simulation of the strengthened beam models based on the finite element have been used [4]. For it, it is necessary the development of numerical constitutive material models capable of simulating what happens experimentally [2].

This paper studies the effect of bonding between concrete and composite plates when epoxy adhesive is used. The results of an analytical and experimental study on the behavior of concrete blocks joined with carbon-fibre-reinforced polymer (CFRP) plates are discussed in this paper.

Several specimens were tested in four point bending through adherence tests. Load-plate strain curves were obtained from these tests.

Numerical analyses included nonlinear finite element modeling incorporating a damage material model [5] for concrete since flexural cracks have an important influence on the load-carrying capacity and the failure mode of the strengthened beam. stress distribution. In general, good correlations were obtained between the experimental results and nonlinear finite element models.

1

Hollaway, L.C., Leeming, M.B., "Strengthening of Reinforced Concrete Structures", CRC Press, Woodhead Publishing Limited, 1999

2

Saadatmanesh, H., Ehsani, M.R., "RC Beams Strengthened with GFRP Plates. I. Experimental Study". Journal of Structural Engineering, Vol. 117, No. 11, 3417-3433, 1991. doi:10.1061/(ASCE)0733-9445(1991)117:11(3417)

3

Triantafillou, T.C., Deskovic, N., "Innovative Prestressing with FRP Sheets: Mechanics of Short-term Behavior", Journal of Engineering Mechanics, ASCE, Vol 117, No 7, 1652-1672, 1991. doi:10.1061/(ASCE)0733-9399(1991)117:7(1652)

4

Oehlers, D.J. , Moran, J.P., "Premature Failure of Externally Plated Reinforced Concrete Beams", Journal of Structural Engineering, ASCE, Vol. 116, No 4, 978-995, 1990. doi:10.1061/(ASCE)0733-9445(1990)116:4(978)

5

Lemaitre, J. , "A Course on Damage Mechanics", Springer , 1996

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