| In recent years, the crack problem of the concrete is more and more outstanding in engineering practice and also such in the bridge engineering particularly, it puts forward the test to the safety and durability of the structure.The fiber-reinforced concrete is a kind of new complex material. This material has excellent capability to restrain bend, crack and bear fatigue.This thesis introduces two kinds of the fiber-reinforced concrete mechanism, namely the composite material theories and the fiber-spacing interval theories, and deduces the formula of the first-crack strength of extension and the ultimate strength of extension of the composite materical. At the same time, The fifteen simply supported beams mixed with the flexible fiber are tested to study the effect of cracking load and stiffness of beam, and crack resistance of structures due to the flexible fiber. Experimental results indicated that the flexible fiber can improve the workability of concrete availably, the cracks of beam are controlled effectively, the width and length of crack decreased, the dispersibility of crack in beam face improved, and the ductility of beam increased; and the cracking load of reinforced concrete beam is increased,the amplify up to about 30%, simultaneity the ultimate bear capacity increased. Besides, SOLID65 element in ANSYS software was used to analyze and simulate these beams, a comparative agreement between theory and experiment was found.The results of the article will enhance the flexible fiber-reinforced concrete application in the bridge engineering.
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