Research On Mechanical Behavior Of Strengthening Bridge With Externally Bonded Prestressed CFRP Sheets

Carbon fiber reinforced plastic(CFRP) has been used widely in strengthening concrete structure as a new material .But the capacity of high strength in CFRP can't fully exert with general strengthening method. The research show that it can improve greatly the performance of the beams with prestressed CFRP sheets. The future study on strengthening reinforced concrete beams with prestressed CFRP sheets is important and valuable.Firstly, this paper introduce the strengthening calculate methods at home and abroad. And then it did nolinear finite elemeant analysis of ultimate bearing capacity using one reinforced concrete beam. The results with FEM simulation are in good agreement with the experimental results. It declared that prestressed CFRP sheets can improve the ratio of utilization greatly. It also proved that the constitutive relation of concrete is reasonable in FEM model.To the extensively used box girder at present, the paper held out the calculate ways of bearing capacity and deflection with prestressed CFRP sheets strengthen box girder. It ansys the mechanical behaviour such as deflection, stress in theory with prestressed CFRP sheets.To solve the cracking problem on top plate, bottom plate, web and midspan downdeflection in the long span continuous box beam bridge, the paper select the continuous rigid frame bridge as a model, use the means of 3-D finite element entity analysis, set several combinations of loads by changing the thickness and stretching prestressing of CFRP to compare stress, deflection and crack. The comparison shows that the prestressed CFRP sheets can improve the character of high strength in CFRP exert effectually, enhanc the flexural capacity. While the research also reveal the behavior that the prestressed CFRP sheets cannot decrease the deflection (rigidity) evidently.Also the paper simulated cracks such as the midspan bottom plate horizontal fractures, one-fourth span incline crack to compare stress and width of crack fore and after strengthening with prestressed CFRP sheets. The comparison shows that the prestressed CFRP sheets can improve the stress, restrain the expansion and distortion of crack. Before strengthening with prestressed CFRP the stress focus on the crack front. However, the normal stress and the principal tensile stress of crack front decrease effectually in bottom plate crack after strengthening. And the shear stress decrease while the principal tensile stress changed not too much in the web incline crack of one-fourth span after strengthening. On the other hand, the powerful prestressing at the end of CFRP make the concrete stress increasing in the same section. So it is necessary to ensure tip anchorage in engineering application of bridge strengthing.