Analysis On Mechanical Behavior Of Reinforced Concrete Beams With Prestressed CFRP

The technology of prestressed CFRP sheet reinforced concrete beams is a new effective technology,in this new technology,prestressed CFRP sheet is pasted on the surface of concrete structure with resin material to generate a new compound structure,so that prestressed CFRP sheet can bear load with concrete structure harmoniously.Generally,some performances of the structure reinforced with prestressed CFRP sheet will be improved and optimized.The paper contains a series of theories and techniques such as mechanics,chemistry,material subjects and so on.It has the special features of discipline-crossing.At the same time the research in the paper possesses theoretical and practical value, so the new technology will have huge social benefits,economic benefits and wide application prospect.In the paper,a series of research is carried out,such as theoretical research and tests and so on.And all the research relies on the project(20040511)of science and technology bureau of Jilin province "The research of theory and technique of CFRP in consolidating and repairing reinforced concrete bridge".The main contents are as follows:â… .Theoretical study 1.Reliability research on the bonding performance of the interface between CFRP and concrete.The bonding strength between concrete and CFRP is a major control parameter in design,and it influences the results of CFRP reinforced concrete beams closely.Based on the theory of elasticity,we established some analytic formulas to calculate the interface shear stress and strain in random position when there is load.Furthermore, we confirmed the distribution law of the interracial bonding strength and CFRP tensile strain.We can see that the analytic formulas are highly accurate.It perfects the bonding theory and can be used in the practical adhesive stress analysis problem of the interface between CFRP and concrete.Subsequently,we demonstrated the conclusion that the flexural analytical formula of the interface shear stress is coincident with the shear analytical formula in theory.Therefore,the torsional low cycle fatigue experiment used to study the fatigue properties of the bonding strength of the interface between CFRP and concrete is more feasible, efficient and precise than the flexural fatigue experiment.2.Theoretical study on pretension control of prestressed CFRP sheet reinforced concrete beams.The technique of the concrete structure strengthened with prestressed CFRP sheet is an effective technique with a bright future. The preliminary tension is an important problem in this technique.And the pre-tension control of reinforced concrete beam strengthened with CFRP decides the buckling stress on the top of concrete beam and interface shear stress between concrete and CFRP.So the author put forward the process of the pre-tension control through theoretical research.And the author demonstrated the excellent efficiency of the concrete structure strengthened with prestressed CFRP in theory.Subsequently,based on the elasticity theory,the thesis presents the interfacial stress models after releasing and loading,and indicates the distribution law of interracial stress,providing the theory foundation for pre-tension control.In conclusion,the paper indicates that the reasonable control on preliminary tension of CFRP is related with the tension stress on the top of concrete beam,the interface shear stress and the increment of interface shear stress between concrete and CFRP after releasing and loading.Only these key factors combine organically,the reinforcement effect could be more obviously.All of these conclusions above provide the foundations for the theory of reinforced concrete beam with prestressed CFRP.3.Research on lamination theory of prestressed CFRP sheet reinforced concrete beams.The reinforced concrete beams strengthened with prestressed CFRP are composed of different materials such as concrete,steel and CFRP, they are quite different in the property of physics and chemistry.And they are also nonlinear.Particularly,the elastic modulus in different location is not homologous under high load when the beam enters plastic state,and the property of physics and mechanics changes,too.So we can regard the structure as a kind of sandwich.But the conventional theory on the prestressed CFRP reinforced concrete beams do not reflect the stress,crack,flexibility and the process of damage concretely. But the information is very important to understand the state of the prestressed CFRP reinforced concrete beams.So the theoretical modes of composite beam based on the state space theory and classical lamination theory are originally put forward for reinforced concrete beam strengthened with prestressed CFRP,the author programmed the nonlinear program that the results of calculations coincide with the results of tests.So we can see that the analytic formulas are highly accurate,some properties of mechanics of this structure can be found.Furthermore,the two theoretical modes based on classical lamination theory and the state space theory can be applied not only to the beam strengthened with prestressed CFRP but also to the others composite beams.But the classical lamination theory is based on the plane-section assumption,so the theoretical mode can be applied only to the structure of small high-span ratio,and the state space theory abnegate the plane-section assumption,so it can be applied not only the beam of the small high-span ratio but also to the deep beam.â…¡.Experimental research1.Experimental research on interface shear.The author researched the strength of the interface through the stretch test by dint of advanced device.In the test,we observed the damage of specimen pasted by CFRP and measured the strain along the stretch direction under different load conditions.2.Experimental research on the torsional low cycle fatigue experiment.The fatigue properties of the bonding strength the interface between CFRP and concrete are studied by use of the new method.At the same time,the results of experiments show that the fatigue bonding strength of the interface between CFRP and concrete is 58%of the static bonding strength in the condition of R=0.2.The problem that the bonding strength of the interface between CFRP and concrete will decrease under fatigue load need to be paid more attention in the design of concrete structure strengthened with CFRP sheets.Therefore,the safety factor of the fatigue strength of the interface between CFRP and concrete should be considered in design.3.Experimental studies on the flexural deformation of concrete structure strengthened with prestressed CFRP sheets.We have carried out the anti-bending tests about 4 pieces of beams. The main purpose is to investigate the flexural capability of the beam strengthened by prestressed CFRP,as well as some phenomenon in different stages.And we investigated the yield load,limit load, deflection and crack in the condition of different preliminary tension. We analyzed the damage mechanism of the structure strengthened by prestressed CFRP and summarized the phenomenon of each stage according to the damage form.Meanwhile,the tests offered the contrast data for theoretical study.We found that the cracking load,yield load,limit load,flexural capacity and rigidity of the reinforced beam strengthened by prestressed CFRP are greatly improved.All of the above parameters are greatly related with the amount and prestress force in CFRP.And the failure mode is different from the beams reinforced with non-prestressed CFRP.In conclusion,these studies in this paper are important advancement to the beam strengthened by prestressed CFRP.And the paper established foundation for the design and observation.