| This thesis precisely summarizes the advantages and disadvantages of traditional strengthening methods for RC structures and analyses the development history and researching status of strengthening methods for RC structures with FRP.On the basis of the theory and experiment researching of Chong Qing JiaoTong University New Composite RC Structure studying group, this thesis gets three mechanisms about strengthening RC structures with FRP based on fracture mechanics principle, analyses the relationship between crack tip stress factor and crack closing length taking use of FEM, points out stress factor of crack tip be reduced and crack extending be resisted by sticking FRP and closing crack, and puts forward that there exists a best length of crack closing, with no need of closing totally. This paper also makes research of shearing strength and normal tension stress distribution law of the interface, it shows that cracks and elastic modulus of strengthening material have a great affection to interface stress distribution, so adopting fiber material whose elastic modulus is approximate to concrete and grouting the existed cracks can effectively improve interface stress.This thesis introduces the GFRP strengthen experiment with repetition and monotonous loads of 6.5×0.6×0.25 (m) and 2.0×0.16×0.1 (m) sized beams. The results show that the rigid, load capacity and ductility of beam have a great improvement after strengthening with GFRP, it has a good consistent with theory analysis.This paper precisely analyses the effect of main bar style on strengthening, puts forward that distortion bar will lead to early destroy of interface. On the basis of experiment and mechanism analysis, this paper constitutes limit load capacity and deflection calculating formulae of positive section of reinforcement concrete beams strengthened with GFRP. The calculate value inosculates with the measured value preferably.
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