الفهرس 
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Abstract
Researchers and industrialist’s interest in fiber reinforced polymer (FRP) to be used as an alternative material to steel rebars in various structural aspects steadily increases. That is due to its advantages over steel rebars. Some of these advantages are corrosion resistance, non-conductivity, high tensile strength and low weight ratio. However, the reinforced concrete (RC) structure constituted by FRP rebars, called FRP-RC, possess less ductile behavior compared to the conventional reinforced concrete. The brittle behavior of FRP-RC structures is mainly due to linear elastic behavior of FRP. The brittle behavior draws back the advantages of FRP when it serves as an internal reinforcement. One of the advantages of the ductility structural system is the ability to redistribute moments over critical sections, which allows more flexibility in structural design. In order to improve the ductility of FRP-RC, it is proposed to add a certain amount of steel rebars in FRP-RC, so the ductility of steel rebars can reduce the brittleness of FRP, called hybrid section.
This thesis investigates the relationship between ductility and moment redistribution in RC, FRP-RC and hybrid section continuous beams. In addition, it calibrates and predicts the redistribution phenomenon of continuous concrete beams for different ratios of steel, FRP and hybrid sections using the self-performed tests in addition to test results available in the literature. Finally, it validates the equations of redistribution moment percentage for beams with different codes suggested for reinforced concrete with steel rebars for FRP and hybrid sections.
Two groups of hybrid reinforcement continuous beams were tested in the experimental program. Each group consisted of three continuous beams. The positive moment reinforcement ratios of GFRP were (μ_GFRP=0.75%) and (μ_GFRP=1.25%). The steel reinforcement’s positive moment reinforcement ratios were varied in order to determine the optimum percentage for working efficiently with GFRP. The main objectives of the experimental program were to evaluate the reinforcement ratio (A_s/A_f) in controlling the performance of the concrete structure, in studying the flexural behavior and load capacity of the beams and in determining experimentally the allowable redistribution.
The numerical program consisted of five groups. The validation of numerical results was confirmed by experimental results, and then parametric studies were conducted to study and evaluate the effects of hybrid sections on the redistribution percentage (β%) of continuous RC beams. group one “S” was reinforced with steel reinforcements based on finite element software (ANSYS). The positive moment reinforcement ratios of steel were 0.75%, 0.67%, 0.56% and 0.4% in terms of the balance ratio. The second “G” and third “C” groups were reinforced with GFRP and CFRP and the positive moment reinforcement ratios were 1.4%, 2.0% and 4.0% in terms of the balance ratio. In all the groups, the ratio between the negative and the positive moment reinforcement ratios ranged from 25% to 200%. The fourth and fifth groups were reinforced with two different types of longitudinal rebars (FRP and steel) in the same section. The positive moment in the fourth group was reinforced with steel and GFRP rebars. However, the fifth group reinforced the positive moment with steel and CFRP rebars. In these groups, the ratio between the negative moment and the positive moment reinforcement ratios was 60%, which was determined previously from steel and FRP groups. The positive moment reinforcement ratios were 0.75%, 1.25% and 1.4%. In order to investigate the effect of different FRP types on the bending moment redistribution of the hybrid section, two additional groups (sixth and seventh) were added. The ratio between the negative and the positive moment reinforcement ratios ranged from 60% to 120%. Finally, a group was calibrated for different arrangements of steel and FRP rebars in order to study the effects of steel and FRP placement in hybrid sections.
The results showed that adding steel rebars to FRP-RC continuous beam improved its ductility by introducing three cracking phases into the load-deflection curve. In addition, a preferable redistribution percentage could be obtained through an appropriate percentage of steel reinforcement compared to the FRP reinforcement ratio of hybrid sections. The main factor in achieving the redistribution percentage in hybrid sections was not only the reserve strength, as mentioned in the literature, but also the ratio between the negative and the positive moment reinforcement ratios that allowed the steel reinforcement to yield in both negative and positive moment reinforcement.