The Research On Precracked Concrete Beams Strengthened With Prestressed Carbon Fiber Reinforced Plastic

Concrete structures strengthened with Carbon Fiber Reinforced Plastic(CFRP)is a new reinforced method. Many advantages such as high strength, light weight,bear to decay, simple construction make it widely used in strengthening field in recent years. While, for CFRP is high in strength, but low in elastic ratio, then only when meet large deformation, can the intensity play fully, but at this time the deflection and the crack width usually exceed the limit state of strengthened component, it is not allowed in actual engineering. Besides, in actual engineering, for generic concrete components, they always working with crack and the one which needs to be strengthened always have crack in a certain width.Appropriate unloading before strengthening may reduce even eliminate the stress and strain lagging phenomenon of CFRP, and then improve the structure integrated bearing capacity. Therefore, in this paper, the beam was completely discharged after being pre-spited, and then was strengthened with CFRP. This method can be used in actual engineering simulating, and it can make full use of high strengthen of CFRP.Based on the experiment of six concrete beams strengthened with CFRP, the different yield load, ultimate load and stiffness were discussed. The influence of the strengthening effect was studied in detail under the scenario analyses of different initial cracking states, different prestress levels and different anchorage styles.Experimental results indicate that strengthening with prestressed CFRP sheets can fully use the strength of CFRP and can effectively improve the load capacity and stiffness of pre-cracked beams. The different pre-cracked degree has less obviously effect on yield load, ultimate load and failure patterns. But it has more effect on the stiffness; the deflection is increased with the increasing of pre-cracked degree with the same load. Suitable anchorage systems can avoid sudden debonding failure, increase the ultimate load, but they have little effect on the stiffness.The paper presents the analytical model based on a strain compatibility and equilibrium of internal forces, and analyses all specimens using the model and presents the yield lode and ultimate load. The formulas are agreed with the experimental results and the formulas can be applied in project for reference.