The Performance Research Of Reinforced Concrete Beam Strengthened With CFRP

With development of national economy and fast increase of traffic flow, running vehicle density and vehicle load capacity are becoming higher and higher, requiring higher bearing capacity of bridges. Among existing bridges, part of them can no longer meet the demand for traffic development due to inferior design in the past years or old and aged structures, endangering normal operation of the bridges. In addition, diseases and damages took place to some bridges built in the 80s due to inferior design or construction quality. Therefore, we have a lot of existing bridges that need to be reinforced or transformed in our country. This is a heavy task. In such engineering background, it is urgent for researchers and engineers to develop a fast, simple, safe, reliable, low-cost, and applicable method for reinforcing and transforming old structures. As a new-type compound material, carbon fiber polymer material has become a favorite of all people in the engineering circle due to its advantages in high tensile strength, light weight, good anti-corrosion performance, and simplicity in construction. We began systematic test study and theoretical analysis on performances of CFRP reinforced concrete beam against stresses by this paper from 2002. We carried out tests and study on 16 bending beams, 5 anchoring beam, 3 fatigue test beams, and 3 temperature test pieces. The scope of our study covers analysis on stress performances, rigidity, attached anchorage, temperature strain, and low- temperature fatigue performances of CFRP reinforced bending beam.Through bending tests on reinforced beam and unreinforced beam by this paper, the influences of carbon fiber reinforcement on bending bearing capacity, rigidity, crack distribution, and steel bar strain of the beams are analyzed. It is proved that the assumption of plane deformation of CFRP strengthened reinforced concrete beam is tenable. The influences of concrete grade number, number of layers of carbon fiber, ratio of reinforcement and other parameters on effect of reinforcement are studied. A computer simulation program has been worked out to calculate the ultimate bearing capacity of carbon fiber reinforced beam by hierarchical method on basis of non-linear finite element principle. The program is used to carry out simulation analysis on the test beams. On such basis, focus is put on study of ultimate tensile strain reduction coefficient of carbon fiber polymer. Analysis is made on the ultimate failure state of carbon fiber polymer reinforced beam. Practical calculation methods for the ultimate bearing capacity under various failure states are described. The specified strength values of materials by the "Codes of Bridge" are adopted to make calculation with simplified formula for our test beams and other authors' test beams. The safety reserves of the simplified formula are discussed.Based on the result of test beams, the law of change of rigidity of carbon fiber polymer reinforced beam cross-section is analyzed. In reference to the calculation method for rigidity of steel reinforced concrete beam in conformity to the structure design principles and taking intoconsideration of the constraint function of carbon fiber polymer, a formula for calculating the rigidity of reinforced beam Bs under combination of short-term load effect during service period is derived, and comparison and analysis are made to the test values and results of other calculation methods. A computer simulation program has been worked out to calculate the deflection of the beam from yield state of steel bars to failure state of the beam. Comparison and analysis are made on the results of calculation by the program and test results.Reasons for spalling of carbon fiber polymer reinforced beams are analyzed by this paper. Through tests on 5 anchoring beams, the forms of failure of the beams are analyzed, and influences of the width and spacing of U-shape strain strakes on the anti-spalling effect of carbon fiber polymer reinforced concrete beam are analyzed.Through tests on three groups of temperature test pieces, the law of change of temperature strain of carbon fiber polymer reinforced concrete beam is analyzed. Based on the principle of compatibility of deformation, analytic solution for the temperature strain of carbon fiber reinforced concrete structural members is derived. Also Ansys software is used to make simulation analysis on temperature strain of carbon fiber polymer reinforced concrete structural members.Under natural low-temperature environment and with fatigue load applied to the test beams by eccentric vibrator, the low-temperature fatigue performances of carbon fiber polymer reinforced concrete beams are analyzed through low-temperature fatigue tests.At last, summary is made on the results of research by this paper, highlighting the innovative points of this paper and problems that are worth further studying.