Experiment Study Of Mechanical Properties Of RC Box Beams Strengthened With Near Surface Mounted Prestressed CFRP Sheets

Carbon fiber sheet (CFS) reinforcement technology has been a rapid development andapplication in terms of structural strengthening because of its good technical advantages. Nearsurface mounted (NSM) prestressed CFS reinforcement is the latest development technology ofCFS reinforcement which combine many advantages of NSM reinforcement and prestressedreinforcement technology. The reinforced concrete thin-walled box beam has been a widely usedin bridge engineering, especially in small and medium span railway simply supported beambridge due to its good mechanical performance. But in the long-term operation, the cracking andbearing capacity caused by various factors affect the durability of box beam. Adopting effectivereinforcement method to improve the box girder bearing capacity and durability is especiallyimportant. In this paper, combining with the Natural Science Foundation of Gansu Province Theinterface stress research of reinforced concrete box beam strengthened with prestressed carbonfiber reinforced polymer, the CFS reinforcement technology research results at the present stagewere analyzed and summarized, then flexural strengthening experiment study has been done forreinforced concrete thin walled box beam, and finally have theoretical analysis andnumerical simulation. The main contents are summarized as follows:(1) The NSM prestressed CFS flexural strengthening experiment study has been done forsingle box single-chamber reinforced concrete box beam with the equipment which is invented to thepretension of the CFRP sheets. The failure mode, the mechanical properties, strain distribution anddeflection pattern of specimens were investigated. Experimental results show that the NSMprestressed reinforcement technology can significantly increase the flexural ultimate bearingcapacity and improve the distribution of internal and deformation.(2) The bending ultimate bearing capacity calculation formula of strengthened beamsdeduced on the basis of the existing reinforced concrete structure design principles. Andconsidering the shear lag effect, assuming the distribution of normal strain on the flanges to be anN-degree parabolic curve, the calculation formula of ultimate bearing capacity under differentfailure modes are deduced according to the elasticplastic ultimate load rule on the basis ofelastic-plastic strain theory and shear lag effect analysis results of variational method. Analyze thetwo kinds of critical failures, propose according to the reinforce amount of CFRP to judge the ultimate failure mode. Comparisons show that the theoretical calculated values agree well withthe experimental results.(3) According to nonlinear finite element theory, the nonlinear finite element of reinforcedconcrete simple box girder strengthened with prestressed CFRP is built using ANSYS finiteelement software. And have a comparison of the finite element calculation results with theexperimental results.