Ultimate Bearing Capacity Of RC Box Beams Strengthened With Near-surface Mounted CFRP Sheets Considering Shear Lag Effect

The commonly used bridge reinforcement methods are enlarging section, bonding steelplate, external prestressing. Carbon Fiber Reinforced Plastic (CFRP) has many advantagessuch as light weight, high strength, corrosion resistance and convenient operation, so it ismore and more widely used in bridge reinforcement. In recent years, many experimentalstudy and theoretical analysis about CFRP strengthening have been conducted, but most ofthem is largely based on rectangular beams and T-beams. The box girder has been widelyapplied in engineering, which has much good performance, such as light weight, hightorsional rigidity, so it is necessary to research on box girder strengthened with CFRP. Justlike the externally bonded CFRP strengthening, the near-surface mounted (NSM) CFRPstrengthening also has the advantages such as improving strength and rigidity of the concretestructures. Besides, it can reduce the impact of extreme environment such as high temperature,high humidity, thawing and refreezing, and improve the utilization rate of CFRP.The main research work in this thesis are as follows:(1) The experiment has been carried on with3box girder with the same size and thesame ratio of steel, among which one is unstrengthened, the other two are strengthened withexternally bonded CFRP and near-surface mounted CFRP. Based on experimental data, themechanical property of reinforced concrete box girder strengthened with NSM CFRP wasstudied.(2) Based on the formulas of normal section bearing capacity, the paper presentsformulas of normal section bearing capacity of reinforced concrete box girder strengthenedwith NSM CFRP. However, when there is pressure stress in the web of box girder, shear lageffect will appear. Therefore, bearing capacity with shear lag is also studied in the paper.(3) Based on transformed section method, shear lag effect of simply-supportedreinforced concrete box girder strengthened with NSM CFRP is analyzed by applyingvariational principle, and calculated result is compared with experimental result, which showsgood agreement.(4) The finite element model of simply-supported RC box girder strengthened with NSMCFRP was built with finite element software ANSYS. By comparison, it is shown that theresult of calculation by ANSYS, result of calculation of this paper, and the experimental resultare close.