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Reinforced concrete deep beams have useful applications in many structures, such as tall buildings, foundations, offshore structures, and several others. The reinforced concrete deep as important structural elements having small span-to-depth ratio. The investigation of their behavior is a subject of considerable interest in RC structures researches and some studies on the shear strength of reinforced concrete deep beams have been carried out over the last fifty years. In deep beams, according to shear span-to-depth ratio and web reinforcement the ultimate strength is generally controlled by shear rather than flexure, if the sufficient amount of longitudinal reinforcement is used. Several different failure modes have been identified from experimental studies, due to variability in failure, the determination of their shear strength and identification of failure mechanism are very complicated. In this paper the influence of effective parameters on the behavior of high-strength RC deep beams was investigated. For this purpose, an experimental-analytical investigation was conducted; a total of five reinforced concrete deep beams with compressive strength in range of 60 MPa were tested under uniform contributed top loading. The tested specimens were simply supported and reinforced by vertical steel bars in various spacing. The general behavior of tested beams was investigated. Observations were made on mid-span vertical deflections, cracks form, failure modes and shear strengths. All the beam specimens showed a same response up to failure. The test results indicated that vertical web reinforcement are efficient in shear capacity of deep beams, all the specimens were failed at abrupt shear mode. According to the test results, the shear capacity is affected by amount of web reinforcement and the test specimens are stronger in comparison with those were tested under two-point loading. Elastic solutions of reinforced concrete deep beams provide a good description of the behavior before cracking, but after cracking, a major redistribution of stresses occurs and hence the beam capacity must be predicted by inelastic analysis. Due to their geometric proportions, the capacity of reinforced concrete deep beams is governed mainly by shear strength. Deep beams behave differently from shallow beams and have been identified as discontinuity regions where the strain distribution is significantly nonlinear and specific strut-and-tie models need to be developed, whereas shallow beams are characterized by linear strain distribution and most of the applied load is transferred through a fairly uniform diagonal compression field. Strut-and-tie method is one of the most simple and applicable methods which can be used to simplify analysis and design of deep beams. Strut-and-tie modeling is the most rational and simple method for designing no flexural members currently available. At least, the experimental strength of specimens was compared with predicted results of strut-and-tie method (STM). The performed comparison indicates that the STM to provide acceptable estimates of shear capacity of deep beam loaded under uniform loading.

Keywords: deep beams, strut-and-tie, Shear Strength, shear reinforcement, contributed top loading

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