Experiment And Analysis On Flexural Behavior Of Prestressed Concrete Beam Reinforced With CFRP Sheet

For the prestressed concrete beam, the crack can close and the deformation can restore after it undergos the ultimate loads. If the local crashed concrete is replaced by the new concrete and the CFRP sheet is used to reinforce the beam, the beam after being reinforced will have good mechanical performance and can be in service.The research on the prestressed concrete beam reinforced with CFRP sheet is limit at home and abroad, and there is no research on the flexural carrying capacity of prestressed concrete beam after ultimate loads reinforced with CFRP sheet. In consideration of this problem, 16 two-span unbonded prestressed concrete beams after ultimate loads reinforced with CFRP sheets are tested. Some status are investigated such as the failure mode, crack and deformation, varitey of stress of unbonded tendons and the plane section assumption at cractical section and so on. The first-hand data are got.Based on the test results, there are three failure modes for the flexural failure of this kind of beam: CFRP sheet breaking after the tensile non-prestressed steel bar yielding, concrete crushing after the tensile non-prestressed steel bar yielding and CFRP sheet separating from concrete. The last kind of failure mode can be avoided with the enough length of CFRP sheet for plastering, the good construction qualitity and setting some U-shaped hoop. Based on the plane section assumption and the constitution relation considering the original damage, the methods are presented to destinguish the two failure mode of CFRP sheet breaking after the tensile non-prestressed steel bar yielding and concrete crushing after the tensile non-prestressed steel bar yielding. The calculation methods for flexural carrying capacity of this kind of beam corresponding to the two failure modes are estabilshed.In the past, all test centres around the simple beam reinforced with CFRP sheets, and there few researches on the continuous beam reinforced with CFRP sheets. Moreover, there are no reserch on two-span unbonded prestressed concrete beam reinforced with CFRP sheets. For this kind of beam from loading to failure, the plastic hinge will occur in the intermediate support region, and concrete at the ultimate fibre in this region will reach the ultimate compressive strain, after that, the plastic hinge will occur in the midespan region, and concrete at the ultimate fibre in this region will reach the ultimate compressive strain. That is to say, there is redistribution of palstic internal force before the two-span unbonded prestressed concrete beam reinforced with CFRP sheets reachs the ultimate state. Basted on the test result, the calculation formulas for the coefficient of moment modification of this beam are set up.In consideration that the calculation formula for crack width and the stiffness of concrete beam reinforced with CFRP sheets are not given in the national industry standard Technical specification for strengthening concrete structures with carbon fiber reinforced polymer laminate (CECS 146:2003), on basis of the summation of test result abroad, the calculation formula for crack width and the stiffness for this kind of beam are put forward.In order to promote the development of prestressed concrete beam reinforced with CFRP sheets, the design and construction propositions are presented including"general principles","materials","design regulations","others"and so on.