| In recent years,fiber reinforced polymers(FRP)are increasingly and widely used in various building and bridge reinforcement projects.Among so many fiber materials,carbon fiber reinforced polymers(CFRP)are the most mature and widely used advanced materials in civil engineering because of their high strength,light weight and corrosion resistance.Furthermore,the CFRP plate which is made from unidirectional carbon fiber impregnated resin has high reinforcement efficiency and controllable construction quality.Meanwhile,the existing results show that strengthening the structure with prestressed CFRP plate can effectively solve the problem of strain lag of reinforcement materials and provide full capability to the strength of materials.For the reinforcement technique of prestressing CFRP plate,the key challenge of the research is a tensioning and anchorage system with excellent stability.However,most of the existing anchorage systems are bulky and difficult to construct,which brings inconvenience to the site construction.The existing anchorage systems for CFRP plates mostly adopt the construction technique of "tensioning after wedging".The counterforce apparatus of these systems will inevitably be retained in the structure after the tension is completed,which makes the operation inflexible.On the basis of previous research,the development of a new anchorage system and its performance test,the construction technique of a corresponding in-situ tensioning system,the flexural performance tests of reinforced concrete T-beams strengthened by in-situ tensioning system,and the theoretical research of reinforced prestressed concrete T-beams strengthened by CFRP plates are studied in this research and the results are presented.The main research objectives are as follows:(1)A wedge-type anchorage is further studied,and the key dimensions of the anchorage are designed and checked based on a thorough stress analysis and finite element method.In view of the unstable anchorage performance of existing wedges,seven different types of wedges are designed and tested.The test simulates the construction technique under real conditions,and the tensioning device is assembled after welding the anchor plate on the ground.The applicability of the in-situ tensioning system is verified,and the ultimate bearing capacity,stress distribution and prestressing loss of CFRP plates are analyzed.(2)According to the design idea of "wedging after tensioning",a set of in-situ tensioning system of prestressed CFRP plates suitable for strengthening concrete structures are independently developed.The system consists of wedge-type anchorage and tensioning devices.The tensioning end anchor is used as the counter-force apparatus of the hydraulic jack in the system,and a dis-assemblable tool anchor is designed,which cannot only reduce the damage of the structure caused by grooving,but also make multiple tensioning possible.It provides a basis for the reinforcement of low elastic modulus materials and large-span structures in the future.The process of strengthening reinforced concrete beams with prestressed CFRP plates based on in-situ tensioning system is established,which provides a basis for compiling technical standards for strengthening concrete structures with prestressed fiber reinforced composite materials.(3)On the basis of flexural performance tests of six beams,the failure characteristics,bearing capacity,stiffness,ductility and crack distribution of reinforced concrete T-beams strengthened with CFRP plates are comprehensively studied and analyzed.(4)Based on the given material constitutive model and calculation assumptions,the upper and lower edge stresses of reinforced concrete beams strengthened with prestressed CFRP plates at the stage of prestressing,and the formulas for calculating the compression moment,yield moment and ultimate bearing capacity of members in normal service stage are derived following the force balance equation.Meanwhile,based on the Code for Design of Concrete Structures,the calculation method of the instantaneous prestressing loss,cracking load and crack width under the effect of short-term load of the concrete beams strengthened with prestressed CFRP plate are introduced.The calculated results are in good agreement with the experimental values. |
