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Project Title: Flexural Behaviour of Hybrid Reinforced Concrete Beams

  • PhD Student: Almahdi Araba
  • Supervisors: Dr Ashraf Ashour and Professor Dennis Lam


Reinforced concrete, in general, is a result of the development of plain concrete and the tendency to have different structures on different scales. The strong and weak characteristics of the latter in compression and tension respectively make it efficient to be used extensively for structures such as foundations, heavy walls and bridge piers. However, the necessity of increasing the capacity of plain concrete in the tension zone, to achieve functionality, safety and economy of structures built to serve the common needs of society has resulted in embedding steel bars into concrete members. This combination of steel and plain concrete is known as Reinforced Concrete (RC).

Reinforced concrete with steel reinforcement has performed well from structural and economic points of view except where structural members have been exposed to severe environmental conditions. Therefore, on an ongoing basis, maintenance and repair due to the corrosion of reinforcing steel will be essential to keep buildings as long as possible. The costly maintenance of structural members has raised the necessity to develop new materials to overcome the degradation of structures.

Fibre reinforced polymers (FRP) which are mainly used in the aerospace industry have appeared as a promising alternative to replace steel rebars due to the nature of the materials used in their fabrication. Their innovative properties such as corrosion resistance, high tensile strength to weight ratio and electromagnetic transparency are the main characteristics that are attractive to the construction industry and structural engineers specifically. In spite of these attractive features, the limited use of FRP in buildings and civil infrastructure has been noticeable. The linear elastic stress-strain behaviour of FRP up to the ultimate strength and the initial cost of FRP are considered as drawbacks. Concrete structures with FRP bars exhibit some ductility which can be considered as a warning to vacate the building in the event of large deformations and can potentially save lives. In addition the low stiffness of concrete structures internally reinforced with FRP bars, due to low modulus of elasticity of FRP, leads to large deformations at the post cracking stage. (Hollaway, 2010)

There are two ways to solve these problems. The most effective way is to improve the material properties of FRP rebar. Structural deformation can be reduced by increasing the elastic modulus of FRP rebars. Mixing different types of fibre materials, such as carbon fibre and glass fibre, are able to change the stress–strain characteristics of FRP rebars in order to improve the ductility of structures.  But these methods are costly. The other way is to combine FRP rebars with steel rebars in concrete components. The function of the FRP bars is to increase the load-carrying capacity, while the function of the steel bars is to ensure ductility of the flexural member upon yielding in tension. (Yinghao and Yong, 2013).


The main aim of the research is to study the behaviour of continuously supported concrete beams reinforced with hybrid reinforcement. The project objectives are summarized below:

  • To experimentally study the structural behaviour of the simply and continuously supported hybrid reinforced concrete beams in comparison with the concrete beams reinforced with FRP bars.
  • To develop an analytical program for predicting the behaviour of simply and continuously supported concrete beams reinforced with hybrid reinforcement.
  • Studying the possibility and the extent of moment-redistribution in continuous concrete beams reinforced with hybrid reinforcement.
  • To examine the applicability of design guidelines against the experimental results of continuous hybrid reinforced concrete beams
  • The commercial finite element modelling software, ABAQUS, will be used to model non-linear behaviour of hybrid reinforced concrete beams.

Research Significance

  • The outcome of this investigation will provide valuable experimental results on continuous beams reinforced with hybrid reinforcement.
  • The experimental results on simply supported and continuous beams can be used for validation of the design guidelines.
  • Engineers and researchers will have a better understanding of the performance of concrete beams reinforced with hybrid reinforcement.
  • The developed numerical technique can be used for further parametric studies to provide more insight into the behaviour of continuous concrete beams reinforced with hybrid FRP-steel bars. 


To achieve the above mentioned objectives, an experimental program will be conducted. The program consists of testing large-scale concrete beams that are continuous over two spans. The test beams have rectangular cross sections and are reinforced with hybrid reinforcement as longitudinal reinforcement. Steel stirrups are utilized as transverse reinforcement.


Hollaway, L. C. (2010). A review of the present and future utilization of FRP composites in the civil infrastructure with reference to their important in-service properties. Construction and Building Materials, 24(12), 2419-2445.‏

Yinghao, L. & Yong, Y. (2013). Arrangement of hybrid rebars on flexural behavior of HSC beams. Composites Part B: Engineering, 45(1), 22-31.‏

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