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|a Concrete is good in compression but week in tension that is, concrete is a brittle material. So, in order to improve the tensile properties, short fibers are used. Effects of steel fibers on flexural performance of reinforced concrete (RC) beams are the main objectives of this study. The hooked-end steel fibers with the dimensions of 0.75 mm in diameter, 50 mm in length and with the aspect ratio of 67 were used in this study. Initially the optimum percentage addition of steel fibers in concrete was determined. In order to accomplish this task, several concrete prisms and cubes with the same mix proportioning of concrete and different volume fractions of steel fiber (0.5 %, 1%, 1.5 %, and 2 %) were prepared. Then, by determining the flexural and compressive strength of samples, it was concluded that the optimum volume fraction was 1 % ( 78.5???? ??3). In the next step,the flexural behavior of RC beams with the addition of steel fibers with lower and higher compressive strength of concrete was considered. The study was conducted on two types of concrete with different grades of 30 and 50. For each grade of concrete, two beams were cast which steel fiber was included in one of the beams, with the addition of 1% volume fraction, and the other beam was considered as control beam. The overall dimensions of the beams were 170 mm in height, 120 mm in width, and 2400 mm in length. The beams were tested under four-point loading test. The results showed that addition of steel fibers in concrete increases the first crackingload, ultimate load, stiffness and ductility of the concrete beams. Furthermore, the addition of steel fibers has more effect on the properties of RC beams with higher concrete grade compared to lower grade.
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