Shear Strength Of Steel Fiber Reinforced Concrete Beams

The shear behavior of high strength concrete beams containing steel fibers have investigated. A total of 17 beams were tested to investigate the influence of fiber reinforcement on the mechanical behavior of high strength concrete beams in shear. The major test variables were the amount of steel fibers, the volume of shear stirrups and the shear span to depth ratio. from test results, it was found that the shear strength of rectangular high strength fiber concrete beams depends mostly on the splitting tensile strength, reinforcement ratio, fiber properties, stirrups ratio, and shear span to depth ratio.The experimental and analytical results on the shear behavior. of the high strength steel fiber reinforced concrete beams show that: ( 1 ) The addition of steel fibers increases the compreSSIve strength by about 28 % and the splitting tensile strength by about 660/0. <( 2) The presence of fibers in concrete restrict propagation of cracks and allow more uniform cracking. (3 ) The failure observed was sudden in the case of beam without fibers and without web conventional reinforcement, whereas beams containing fibers, failed gradually. This is because of the crackarrest mechanism exhibited by steel fiber and due to interfacial bond strength of steel fibers. ( 4) The presence of high percentage of steel fibers transformed the mode of failure of the tested beams into a more ductile one and increased the number of diagonal cracks formed. ( 5) The mode of failure has been changed from shear to flexural type when the volume fraction of fibers was increased beyond an optimum value. For example, in beam with fiber content ( vf) = 0.75 % and shear reinforcement ratio (v.) = 0.57 0,/0, the failure occurred due to cracks in the flexure span.( 6) The vertical deflections and longitudinal proportional to the shear span to depth proportional to fiber volume fraction.strains are directly ratio and inversely (7) The fiber inclusion greatly increases the cracking shear strength.Thus, the addition of steel fibers gives rise to a larger increase in cracking shear strength and ductility. For example, for beams with (a / d) = 2 and without stirrups when the fiber volume fraction was increased from 0 % to 0.75 %, there was an Increase in cracking shear by about 9.1 percent and by about 25 percent when the fiber volume fraction was increased from 0.75 0,/0 to 1.5 %. while, for (a / d) = 3 there was an increase by 25 percent when the fiber content was increased from 0 to 0.75 % and by 20 percent for increase in fiber content from 0.75 to 1.5 %.