عبد الرزاق عبد الحسين شاهينأ.م.د علي كريم رزاق2024-11-062024-11-062021-11-27https://dspace.utq.edu.iq/handle/123456789/196This research aims to experimentally investigate the flexural behavior of reinforced concrete beams with hybrid fiber. For this purpose seven mixes were studied, one control mix without fibers and six hybrid fiber mixes were prepared consisting of different ratios of steel fibers and polypropylene fibers. Steel fiber crimped was an aspect ratio 50 and volume fractions of 0.5%, 1%, and 1.5% , while the polypropylene fiber used had an aspect ratio 375 and volume fractions of 0.15% and 0.3%. Superplasticizer was added in a ratio of 1.5% and the ratio of water to cement was constant in all concrete mixtures and equal to 0.47. In the present study, cubes (150 x 150 x 150)mm were casted for compressive strength test and cylinders (150 x 300)mm to obtain the compressive stress-strain diagrams for each mix. Fourteen reinforced concrete beams with dimensions of (120 x 200 x 1200) mm were casted. All beams were tested under three point loading, seven beams under the static load and the other seven under the repeated load . The load-deflection curves characteristic, ultimate load, and cracking behavior were observed and studied. Additionally, the effect of hybrid fibers on concrete properties has been investigated, and failure patterns in specimens were recorded and discussed intensively. The experimental results indicated that the increase in the hybrid fiber content led to decrease of the workability. All concrete mixtures showed improvement in compressive strength test results due to the effect of the hybrid fiber on the final resistance properties. As a result of the effect of the hybrid fiber, the number of cracks has increased and the distances between them were reduced. However, the cracking pattern caused by the repeated loading was more segmented and extensive than the static loading pattern. These results indicated an increase in the ductility of the concrete and thus improved the structural performance of the beams. The load-carrying capacity of beams was increased by adding the fibers. The highest improvement in compressive strength and ultimate load compared to the plain concrete was 27% and 14%, respectively. This was obtained from including 1% of steel fibers and 0.3% of polypropylene fibers in the concrete mix. Repeated loading has no significant influence on the ultimate load-carrying capacity of the tested beams, but deflections and propagation of cracks increased successively. In addition to that, the vast majority of cracks number were occurred during the first loading cycle. Evaluation of the load-deflection curves of hybrid fiber reinforced beams under static and repeated loads that fibers contribute significantly to maintaining the structural integrity and stability of the concrete. The analytical equations were used in this study indicated the Zhang et. al (2018) analytical model give closer prediction of the flexural strength of beams with hybrid fiber than ACI 544 model. In conclusion the combining of polypropylene and steel fibers improves the multiple properties of a concrete mixture, which can contribute of the prolonging the service life of the buildingentext::thesis::master thesis