The widespread use of concrete and concrete structures provide pursuant to the coming new requirements in technology and design of these structures. Combine different technologies to improve performance and increase the effectiveness of this type of structure is one of the paths of research and development. One of these ideas combine the use of lightweight concrete (LWC), micro and macro fibers and FRP bars. The main purpose of this experimental study is to investigate the effect of fibers and hybrid fibers on the shear strength of LWC beams reinforced with GFRP bars. Firstly, twelve concrete mixtures with different volume fractions of made with micro glass fiber (GF), micro polypropylene fiber (PF), and macro steel fiber (SF) were tested up to compressive strength to determine the optimum fiber content of GF, PF and SF added into LWC. Then, three LWC rectangular cross-section beams with 1500mm length × 100mm width × 200mm depth were cast made with the optimum fiber content of GF, PF and SF and also four LWC beams made with hybrid fibers “GF + PF”, “GF + SF”, “PF + SF” and “GF+PF+SF” with the combinations of the optimum percentage which previously had been found for the fibers. Finally, one beam was made with pure LWC. All beams were reinforced with two GFRP bars having 8mm diameter without shear reinforcement and tested up to failure under four-point bending. The experimental results showed that the fibers and hybrid fibers added into LWC improved the shear strength and increased ultimate load carrying capacity from 55% to 233% relative to the pure LWC beam. Meanwhile, a shear strength correction factor (α) for LWC reinforced with GFRP bars with and without added fibers determined, which was calculated from comparing the experimental results with ACI 440.1R-06, CSA-S806-02, ISIS Canada-01, and JSCE-97 formulas.

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