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Bond behaviour of Fibre Reinforced Polymer (FRP) Re-bars in Concrete

  • PhD Student: Najia Saleh
  • Supervisors: Dr Ashraf Ashour, Professor Dennis Lam and Dr Therese Sheehan

Background

In the presence of corrosive environments, reinforcing steel bars in concrete structures may suffer severe deterioration due to corrosion. Therefore, it has been a primary concern for researchers and engineers to control the corrosion of steel reinforcing bars. As a result, steel re-bars are substituted with alternative reinforcement. It has been found that fibre reinforced polymer (FRP) re-bars are the appropriate alternative (Neale and Labossiére, 1992; Nanni and Dolan, 1993; Tighiouart et al., 1998). FRP reinforcing bars have several advantages over conventional reinforcing steel, for instance non-corrosiveness, high tensile strength, light weight, fatigue resistance, nonmagnetic electrical insulation, small creep deformation and specific gravity (Hao et al., 2006).

Consequently, FRP reinforcing bars have been introduced as reinforcement for different concrete structures subjected to aggressive environments such as chemical and wastewater treatment plants, sea walls, floating docks, and under water structures (Benmokrane and Rahman, 1998; Saadatmanesh and Ehsani, 1998; Dolan et al., 1999). In spite of the advantages of FRP reinforcement, FRP suffers from some problems.

The main problems that prevent the use of FRP re-bars extensively as a reinforcing material for concrete structures are:

  • FRP has linear elastic behaviour up to failure. It means no ductility.
  • The modulus of elasticity for some types of FRP, for example aramid fibre reinforced polymer (AFRP) and glass fibre reinforced polymer (GFRP) is much lower than steel, hence deflection and crack widths may control the  design of reinforced concrete structures.
  • The bond behaviour of FRP re-bars with concrete is different to that of steel re-bars due to the non-isotropic material properties and the different surface texture of the FRP re-bars (ACI 440.1R-06).
  • The higher cost of FRP compared to steel, lack of familiarity with the new technology and limited availability of literature has contributed to the slow adaptation of FRP as concrete reinforcement (Okelo and Yuan, 2005).

The performance of a reinforced concrete member, both at the ultimate limit state (strength) and the serviceability limit state (crack and deflection), depends on the transfer of forces between the concrete and the reinforcement, which depends on the quality of bond between the two materials. Therefore, many experimental studies have been conducted to understand the bond behaviour of FRP re-bars embedded in concrete. Despite the numerous experimental investigations, the bond behaviour of FRP re-bars with concrete is not completely understood yet because of the complexity of the parameters influencing the bond behaviour such as type of FRP, the type of bar surface, bar diameter, embedment length and concrete compressive strength.

Aims

The main purpose of this study is to investigate the effect of different parameters such as the type of FRP bar, bar diameter, embedment length, the type of FRP surface, compressive strength of concrete on the bond behaviour of FRP re-bars embedded in the concrete. The objectives of the current research are as follows:

  • To collect experimental data from previous studies in order to predict the bond strength by using Artificial Neural Networks. The ANN model has been prepared to predict the bond strength. Figures (1-3) demonstrate predicted bond strength with different factors.
  • To use two methods to measure the bond strength experimentally: pull-out tests and beam tests.
  • To use the finite element package (ABAQUS) to model the concrete member reinforced with FRP re-bars in order to develop the bond stress – slip relationship.

Research Significance

A limited number of researchers have used the beam test to examine the bond behaviour of FRP re-bars to concrete; consequently the current research will concentrate on carrying out beam tests. The beam method is more realistic than the pull-out test.

Methodology

To perform the aims and objectives that are mentioned above, the following methods will be utilised:

  • Pull out and beam tests will be carried out.
  • The use of the finite element package (ABAQUS Software) to model concrete elements reinforced with FRP re-bars.
  • A numerical program (ANN) will be developed to predict the bond strength.

Figure 1. Effect of development length on bond strength.

Figure 1. Effect of development length on bond strength

Effect of bar diameter on bond strength

Figure 2. Effect of bar diameter on bond strength

Effect of compressive strength of concrete on bond strength

Figure 3. Effect of compressive strength of concrete on bond strength

References

ACI Committee 440 (2006). “Guide for the design and construction of structural concrete reinforced with FRP bars (ACI 440.1R-06).” American Concrete Institute, Farmington Hills, MI.

Benmokrane, B., and Rahman, H., eds. (1998). First Int. Conf. on Durability of composites for construction, CDCC’98, Sherbrooke, Què., Canada.

Dolan, C. W., Rizkalla, S. H., and Nanni, A. eds. (1999). Proc., 4thInt. Sym. Fibre Reinforcement Polymer Reinforcement for reinforced concrete structures, FRPRCS-4, ACI SP-188, Baltimore.

Hao, Q. D., Wang, B., and Ou, J. P. (2006). “ Fibre reinforced polymer rebar’s application to civil engineering.” Concrete, V. 9, pp. 38-40.

Nanni, A., and Dolan, C. W. (1993). “Fibre reinforced plastic reinforcement for concrete structures.” International Symposium, SP-138, American Concrete Institute (ACI), SP-138, pp. 977.

Neale K. W., and Labossiére P. (1992). “Advanced composite materials on bridges and structures.” First International Conference, Canadian Society for Civil Engineering, Sherbrooke, Québec, pp. 700

Okelo, R., and Yuan, R. L. (2005). “Bond strength of fibre reinforced polymer re-bars in normal strength concrete.” Journal of Composites for Construction, V. 9, No. 3, pp. 203-213.

Saadatmanesh, H., and Ehsani, M. R., eds. (1998). “Fibre composites in infrastructure.” Proc., 2nd Int. Conf. on Composites in Infrastructure, ICCI’98, Tucson.

Tighiouart, B., Benmokrane, B., and Gao, D. (1998).“Investigation of bond in concrete member with fibre reinforced polymer (FRP) bars.” Construction and Building Materials,V. 12, pp. 453-462.

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