Keywords: shear, capacity, composites, concrete.

Fiber reinforced plastic (FRP) bars are recently used as an alternative to steel reinforcement to overcome the corrosion problem of steel reinforced concrete structures in a severe environment. The mechanical properties of FRP bars are different from those of steel bars; however, they are dependent on the type and amount of fibre and resin. Generally, FRP bars have a lower weight and a lower modulus of elasticity but higher strength than steel. In addition, the stress-strain curve is straight up to failure, exhibiting a brittle nature.

Research into shear behaviour of FRP reinforced concrete beams has received less attention than that into their flexural behaviour. The ACI Committee 440 guidelines [1] for the design and construction of FRP concrete structures pointed out that the concrete contribution to shear resistance of beams reinforced with FRP bars is still unclear and future research is needed to provide information in this area.

This paper presents test results of twelve concrete beams reinforced with carbon fibre reinforced plastic (CFRP) bars. All beams were tested under a four point static loading system to investigate shear behaviour of CFRP reinforced concrete beams. Different arrangements of longitudinal CFRP bars and transverse steel links are investigated. Beams are classified into three groups according to the beam depth. In each group, two beams had no vertical stirrups, whereas the other two were reinforced with 8mm diameter vertical steel stirrups at 150mm spacing. Beams with no vertical steel stirrups exhibited a diagonal shear failure crack at almost 45^o, but those reinforced with vertical steel stirrups failed in a much steeper diagonal shear failure crack. The amount of longitudinal bottom CFRP reinforcement had no significant effect on the shear capacity of beams tested without vertical links. However, the amount of longitudinal bottom CFRP reinforcement does have a more significant influence on the shear capacity of beams tested when combined with vertical steel links.

Comparisons between shear capacity calculated from five different methods recently developed in the literature [1,2,3,4,5] and that measured in the current study show inconsistent agreement. The ACI-440 method for estimating the shear capacity of CFRP reinforced concrete beams was very conservative, while Deitz et al. formula [4] significantly overestimated the shear capacity of the CFRP reinforced concrete beams tested. Michaluk et al. method [5], in which the shear capacity is estimated by modifying the conventional steel shear capacity formula using the ratio of the modules of elasticity of CFRP and steel bars, provided a reasonable prediction for the shear capacity of the CFRP concrete beams without vertical links tested. The addition of shear capacities provided by concrete and vertical steel links is highly unconservative for CFRP reinforced concrete beams having vertical steel links. Further experimental research is needed before a rational model for the shear capacity of FRP reinforced concrete beams with and without transverse reinforcement could be established. Other types of FRP reinforcement including glass fibre reinforced polymer (GFRP) and aramid fibre reinforced polymer (AFRP) should be investigated. Additional experimental work should be conducted to investigate the effect of other arrangements of longitudinal and transverse reinforcements on the shear capacity of FRP reinforced concrete beams.

1

ACI Committee 440, "Guide for the design and construction of concrete reinforced with FRP bars", American Concrete Institute, Farmington Hills, Michigan, 41 pp, (2001).

2

Tureyen, A.K. and Frosch, R.J., "Concrete Shear Strength: Another Perspective", ACI Structural Journal, Vol. 100, No. 5, pp. 609-615, 2003.

3

Alsayed S.H., Al-Salloum, Y.A. and AlMusallam, T.H., "Shear design for beams reinforced by GFRP bars", Proceedings of the Third International Symposium on Non-Metallic (FRP) Reinforcement for Concrete Structures (FRPRCS-3), Japan, Vol. 2, pp. 285-292, (1997).

4

Deitz, D.H., Harik, I.E. and Gesund, H., "One-way slabs reinforced with glass fiber reinforced polymer reinforcing bars", ACI proceedings, The Fourth International Symposium, Detroit, pp. 279-286, 1999.

5

Michaluk, C.R., Rizkalla, S.H., Tadros, G. and Benmokrane, B., "Flexural behavior of one-way concrete slabs reinforced by fiber reinforced plastic reinforcements", ACI Structural Journal, Vol. 95, No. 3, pp. 353-365, 1998.

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