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Abstract

Steel fiber can improve the shear strength , flexural strength , ductility and fatigue of concrete. The range of proportion for deformed steel fiber in 3/4 in. maximum-size aggregate which proposed in ACI standard was 0.3-0.8 volume precent of concrete. This article presented the behavior of RC beam with exceeding steel fiber under cycling loading. Beam section 12x24 cm2 with two 12 mm dia. bars in both tension and compression sides and varying the amount of fiber at 0.0 , 0.5 , 1.0 and 1.5 volume precent of concrete was conducted under cyclic four point bending test. It was found that steel fiber , not more than 1.0 volume present, led to the increase of tensile strength of concrete. Nevertheless, the compressive strength and flow ability were worse, especially of steel fiber at 1.5 volume present. For the beams under cyclic loading at 80% of section capacity, the steel fiber reduced the damage and increased the ultimate strength of the beam. However, the concrete with more steel fiber than the ACI suggestion contributed to the decrease of flexural crack distribution and collapse suddenly from the break of tension rebar.