الفهرس 
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Abstract
In aggressive environmental conditions, steel reinforcement is exposed to corrosion,
therefore significant deterioration in structural integrity is expected of RC buildings. Fibrereinforced polymer (FRP) bars have emerged as a non-corrosive alternative to steel for RC
components exposed to such conditions. Due to their non-corrosive characteristics, several
investigations were conducted to address the use of FRP products to proxy steel bars in reinforcing
concrete structures. Based on these investigations, several standards have involved FRP as a
reinforcing element for concrete and design procedures have been formulated. Nevertheless, the
inconsistent thermal characteristic between FRP and concrete and the non-yielded-before-failure
of FRP still needs more investigation. In addition, the relatively low modulus of elasticity of FRP
bars, in many cases, can lead to significant cracks and excessive deflections and, therefore, violate
the serviceability of the element. In this context, the characteristics of hybrid rebar that is combined
with different FRP materials have been addressed in the present thesis.
This hybrid consists of a fuse of carbon fibre and glass fibres which aims to improve the
structural performance of GFRP-reinforced concrete members. One alternative solution has been
proposed using a hybrid reinforcement (GFRP and CFRP rods) as the main reinforcement. Using
two different hybridization techniques, the new hybrid rebar manufacturing was addressed in this
thesis in order to enhance the fuse by using carbon fibre which provides higher tensile strength
and modulus of elasticity compared to conventional steel. Even though, the advantageous features
of using carbon fibre in enhancing the mechanical properties of the FRP, the economic feasibility
of using such a hybrid on an industrial scale is still an open issue. In this context, the concept of
“hybridization” was arisen for the FRP rebar to overcome its shortcomings.
This study demonstrates the behaviour of bending conditions and serviceability of
concrete beams reinforced with FRP rods and hybrid rods under constant loads through theoretical
and experimental analysis for each of them with a size of 150 x 250 x 2400 mm. All the
experimental specimens were tested using a four-point loading test. A large number of specimens
were prepared and tested in order to address the effect of several parameters namely the grade of
concrete reinforcement ratio and CFRP-to-GFRP hybridization ratio (CFRP/CFRP + GFRP). In
addition, as prominent engineering demand parameters, the deformations of concrete and
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reinforcement, cracks’ width and their pattern were measured and analyzed. The experimental
results are summarized and compared with existing theoretical models.
First, the mechanical properties of the hybrid rebars were tested to investigate in order to
optimize the manufacturing process. As such, the bars were subjected to both tensile and shear
strength tests in order to investigate their structural behaviour and find a correlation between the
results. The obtained results demonstrated the structural adequacy of the hybrid rebar compared to
GFRP. Given the importance of SLS for such hybrids, the results have been discussed in light of
the serviceability components. As such, crack type, ultimate modes of failure, load bearing
capacity, service load, CFRP rod, tensile strain in steel and GFRP, mid-span deflection, concrete
strain, crack spacing, and crack width were recorded and analysed. It was concluded that the
mechanical characteristics of hybrid composites are affected by the mix ratio of reinforcing fibres
(hybrid ratio). Furthermore, Young’s modulus drops almost linearly as the hybrid ratio of carbon
fibres is decreased, while the tensile strength remains constant and fracture energy proportionally
increases.
As well-established in the literature that low- or over-reinforced sections alter
serviceability or ultimate strength limit state, respectively, a proposal for the design of FRPreinforced concrete section has been introduced. Based on regression analysis, several equations
to predict the performance of concrete beams reinforced by the hybrid bars were driven. The
efficiency of these proposals were evaluated in light of the existing model and real experimental
data. Based on these comparisons, it can be concluded that the combination of carbon fibres and
basalt fibres leads to a more cost-efficient alternative to Carbon FRP (CFRP) and a more
sustainable alternative to GFRP.