Study On Flexural Behavior Of Self-stressing Reinforced Concrete Beams Externally Wrapped By CFRP

Carbon fiber reinforced polymer(CFRP)is increasingly welcomed by engineers in civil engineering for having superior properties such as high strength-to-weight ratio,corrosion resistance,construction convenience and so on.In recent years,the beam fabricating method of incorporating CFRP enclosure and expansive concrete was proved to be a portable and effective way to apply prestress to the concrete and CFRP.As during the expansion of the concrete,external CFRP enclosure performed as a restraint role in this process.This interaction between expansive concrete and CFRP enclosure generated self-prestress in them after the concrete hardened.But some drawbacks of large crack width,less crack quantity,poor ductility and brittle failure also appeared in the bending tests of these concrete beams reinforced with CFRP enclosure when compared to the steel reinforced concrete ones.So,for limiting crack width and improving ductility,a certain amount of longitudinal steel was added in this system and a new beam system-self-stressing reinforced concrete externally wrapped by CFRP was put forward in this thesis with the support of Natural Science Foundation of China(51208077).And the flexural behavior of the new system was investigated.The main research work are as follows:(1)Study on the flexural behavior of the self-stressing reinforced concrete beams externally wrapped by CFRPTen beams were fabricated,five conventional concrete beams and five expansive concrete beams,in this experiment.Experimental variables included the type of concrete,steel reinforcement ratio and CFRP reinforcement ratio.Flexural test results and analysis showed that reinforced concrete beams externally wrapped by CFRP performed better than conventional reinforced concrete beams in cracking load,load of serviceability limit state,ultimate load carring capacity,flexural stiffness and ductility.Furthermore,the self-stressing reinforced concrete beams performed better than the conventional reinforced concrete beams externally wrapped by CFRP in all the aspects mentioned.(2)Flexural behavior comparison of prestressed CFRP reinforced concrete beams by two different tensioning methods of prestressingIn order to investigate the flexural behavior of expansive concrete beams reinforced with unsymmetrical CFRP enclosure and compare the flexural behavior of self-stressing reinforced concrete beams externally wrapped by CFRP and conventional concrete beams strengthened with prestressed CFRP sheets at the same prestress level.Ten beams have been fabricated in total including four conventional concrete beams and six expansive concrete beams.Experimental variables included the type of concrete,tensile CFRP reinforcement ratio,compressive CFRP reinforcement ratio and the prestress level of CFRP.The expansion strain of expansive concrete was monitored and the prestress level in it was compared.Cracking load,ultimate load,flexural stiffness and crack width of ten beams were also compared through bending tests.(3)Calculation model development and theoretical analysis of crack width of reinforced concrete beams externally wrapped by CFRPOn the basis of the first series of tests,new equations for calculating crack width of reinforced concrete beams externally wrapped by CFRP were put forward based on the equations proposed by JTG D62-2004 and Frosch through regression analysis.Theoretical values are in good agreement with experimental results.(4)Analytical model for calculating cracking load and ultimate load of self-stressing reinforced concrete beams externally wrapped by CFRPOn the basis of the second series of experiment,new analytical model and equations for calculating cracking load and ultimate load of self-stressing reinforced concrete beams externally wrapped by CFRP were put forward through rigorous theoretical analysis,reasonable assumptions and proper simplifications.The theoretical ultimate loads showed good agreements with experimental results.