Experimental Research Of CFRP Strengthened Reinforced Concrete Box Beams Subjected To Combined Action Of Bending-Shear-Torsion

In recent years, with the increasing of traffic volume, the early structure of bridge have different degrees of disease, because of many advantages, CFRP reinforcement technology is used widely by engineer. Study of domestic and foreign scholars studied a large number of theoretical analysis and experimental research about the mechanical property and usability of CFRP reinforced concrete structure. CFRP reinforcement has been used widely in the reinforcement of reinforced concrete beam bending and shear, but study of torsional behavior of CFRP strengthened reinforced concrete box beams was not a lot, especially the study of torsional behavior of CFRP strengthened reinforced concrete box beams subjected to combined action is less. In this dissertation, a systematic study on the experiment and theory of torsional behavior of CFRP strengthened reinforced concrete box beams subjected to combined action of bending moment, shear force and torque were studied. The following work are included:1. Made of five test beams, including a non strengthened control test beam and four pieces of reinforced by different ways. Test loading device is YJ- IIID type mechanical structure combined test device of Yantai Xintiandi Test Technology Co. Ltd. and Lan Zhou Jiao Tong University jointly design and special loading equipment, the loading tests of four cases.2. The test data of each piece of the test beam on elastic stage under the action of the pure torsion stress was performed, and then find out a good reinforcement method to improve the torsion performance of box beams. The failure formation, development of cracks, the strain of steel, the strain of concrete, the strain of CFRP of box beams subjected to combined action of bending-shear-torsion was performed. The results of the research stated that, the torsional strengths of reinforced concrete box beams were enlarged obviously the stiffness of box beams were expanded and the deformation behavior of them were amplified obviously.3. Before cracking of box beams, used force analysis of Mohr's circle and based on the experimental research, a new mathematical model for cracking torque of CFRP strengthened reinforced concrete box beams subjected to combined action was developed. After cracking of box beams based on the variable-angle spatial truss model. The torsional strengths of reinforced concrete box beams was calculated by the stress of longitudinal paste CFRP and the ring paste CFRP taken into account, and the calculation result is consistent with the test results.4. The finite element model of CFRP strengthened reinforced concrete box beams was established by ANSYS, the Stiffness of the deformation and the strain of concrete of simulation box beams in elastic stage simulation of pure torsion loads, and the results are compared with the experimental values. By comparing the calculation results of ANSYS and the experimental results agree well, which indicates that the box beams model can accurately analyze the stress and strain of box beams load under pure torsion.