الفهرس 
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Abstract
Lightweight reinforced concrete contains polypropylene fibers has proven to be economical in building construction as it reduces its cost and, therefore, the main objective of this research is to study the influence of polypropylene fibers on the behavior of lightweight reinforced concrete beams and, as well, to highlight the main role of polypropylene fibers on the concrete properties, in general, to improve ductility, stiffness, crack width and ultimate capacity and to investigate the effect of variable parameters such as: (1) main steel ratio, (2) polypropylene fibers content, (3) fiber aspect ratio. Experimental and numerical programs were used to study the behavior of lightweight concrete (LWC) beams contains polypropylene fibers. The experimental program consists of eight simply-supported beams which divided into three groups in addition to the control beam. All specimens were tested and loaded in the lab with two concentrated loads. All beams had the same rectangular section (100mm × 300mm) and clear span 1800 mm. The first group of specimens studied the effect of main-to-max. steel ratios ( / max) with constant fiber content Vf of 0.1% and aspect ratio of 90. The second group studied the effect of fiber contents Vf of 0.05 and 0.2% with a constant ratio of ( / max) of 0.47 and aspect ratio of 90. The third group had fiber aspect ratios of 60 and 30 with a constant main ratiof / max) of 0.47 and fiber content of 0.1% to study the effect of fiber aspect ratio on the behavior. The control specimen (lightweight reinforced concrete beam without fiber) has / max) of 0.47 which was used as a reference (control) specimen. To assess the accuracy of the experimental results, a three-dimensional nonlinear finite element analysis using ANSYS program was performed. ANSYS program was used to calculate ultimate loads for beams previously tested by other researchers. It was also used to model and calculate the ultimate loads of twenty-three reinforced concrete lightweight reinforced concrete beams with polypropylene fibers. Finally, the experimental and the numerical results were compared to those calculated using the ACI 318-19 code, and the comparison was most satisfactory.