The use of fiber reinforced polymer (FRP) rebars, which has become popular in recent years due to their significant corrosion resistance and high tensile strength, are considered an important alternative to steel reinforcement. However, FRP rebars show brittle behavior and rupture at low strain values without yielding deformations. The researchers generally state that ductility is the main concern in FRP reinforced concrete (RC) beams. In order to overcome to the corrosion problem of steel bars and the ductility problem of FRP bars, hybrid FRP-steel RC beam design, in which steel and FRP reinforcement are used together in the tension zone, have been implemented in numerous studies. In these beams, steel reinforcement yields before reaching ultimate capacity, and thus, a certain level of ductility can be guaranteed. Researchers have different opinions on the suitable ductility definition for these beams and a minority of these researchers are in the favor of using the classical deformation ductility definition. However, the ductility of hybrid RC beams cannot be evaluated through the classical definitions. The classical definitions erroneously imply that the ductility of a hybrid RC beam increases with increasing amount of FRP within the total (steel+FRP) tension reinforcement. This inaccurate trend stems from the fact that steel reinforcement yields at lower load levels in hybrid RC beams with a relatively higher FRP ratio and the total deflection capacity tends to increase due to the low modulus of elasticity of FRP. In the present study, an energy-based method is proposed for hybrid FRP-steel RC beams. This method proved to show the correct trend in ductility with the variation of FRP in the total tension reinforcement according to the experimental results of the authors.
Anahtar Kelimeler: Ductility, FRP reinforcement, Hybrid
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