Experimental Study Of High Strengthened Concrete Flexural Members With Prestressed CFRP

Modern construction are no longer satisfied with the existing forms.A variety of novel structures are put forward on the basis of super-tall and long-span structures,which make the high-strength concrete widely used.It is inevitable that concrete structure will be damaged during service,strengthening damaged structure is a problem that needs to be solved in modern engineering field.CFRP is used in the field of reinforcement by virtue of its high strength and corrosion resistance.However,most of the existing studies only focus on ordinary concrete members,and whether it is applicable to high strength concrete structures remains to be studied.This paper is part of the project of National Natural Science Foundation of China?51378089?.The flexural behavior of concrete members strengthened with CFRP under different prestressing levels and different sizes and the effect of CFRP reinforcement are studied,and the calculation formula of flexural bearing capacity of prestressed CFRP strengthened beams is established.The results of calculation and test are compared and analyzed,and the prestressing loss and optimum prestress level of RC beams strengthened with CFRP with different prestressing levels are studied,and the range of optimum prestress levels is put forward.The main research results are as follows:?1?The comparative study of prestressed CFRP reinforced concrete specimens and high strength concrete specimens is carried out.The results show that the failure patterns of the strengthened specimens are close to the interface failure caused by the bending and shear cracks in the middle part of the specimens.Prestressed CFRP can obviously improve the strengthened specimen bearing capacity,restrain the crack development and improve the utilization ratio of CFRP.The peeling failure of the strengthened specimen is gradually changed from the destruction of resin adhesive layer to the destruction of the interface between adhesive layer and concrete,and with the increase of prestress grade,the ductility of reinforced concrete strengthened specimen is improved obviously.?2?The flexural behavior of high strength reinforced concrete beams strengthened with prestressed CFRP is studied.The results show that the increase of beam size has no obvious effect on the strengthening effect of prestressed CFRP.The ductility of unstrengthened beam is higher than that of ordinary CFRP strengthened beam,but with the increase of CFRP prestress grade,the ductility of prestressed CFRP strengthened beam is obviously improved.When the prestress grade reaches 30%,the ductility of strengthened beam is basically the same as that of unstrengthened beam.The failure forms of prestressed CFRP strengthened beams are all the interface debonding failure caused by bending and shear cracks in the middle part.The calculation formula of flexural bearing capacity of RC beams strengthened by prestressed CFRP is established,and the calculation results and test results are given.The calculated results are in good agreement with the experimental results.?3?The prestress loss and optimum prestress level of high strength reinforced concrete beams strengthened with prestressed CFRP are studied.The results show that with the increase of prestress grade,the bearing capacity of strengthened beams increases significantly,and the ductility of strengthened beams is obviously improved by prestressed CFRP within a certain prestress level,and the prestress loss mainly occurs during the deformation of anchors and prestressing tensioning.The higher the prestress grade of CFRP is,the greater the strain loss is.Considering the prestress loss,test analysis and calculation analysis,it is suggested that the optimum prestress level should be in the range of 25%f_cfk⁴0%f_cfk.