Study On Flexural Behavior Of ECC-NC Composite Beams Reinforced By CFRP Textile

Engineering cementitious composites(ECC)have the advantages of high ductility,high durability and multi-joint cracking,which can effectively solve the problems of poor crack resistance and brittle failure of concrete.Fiber reinforced polymer/plastic(FRP)has the advantages of light weight and high strength,two-way force,convenient construction,suitable for harsh environments such as corrosion and cold,and can also show good durability,fire resistance and peel resistance when used with polymer mortar.Among them,carbon fiber reinforced polymer/plastic(CFRP)has high modulus of elasticity,tensile strength,fatigue resistance and corrosion resistance in all FRPs.The CFRP grid is embedded inside the ECC,which can not only exert the plasticity of ECC,but also exert the high strength and corrosion resistance of CFRP materials.In this paper,ECC replaces the concrete at the bottom of the tensile zone of the beam body,and places the FRP grid inside the ECC layer,and the flexural performance of the CFRP grid enhances the ECC-NC stacked beam,mainly from the following aspects:(1)The material properties of the materials required for this test were tested,and a constitutive model was established for finite element simulation and theoretical analysis of the later superimposed beams.(2)The four-point loading test of RC beam and ECC-NC superimposed beam with different parameters was carried out,and the crack development and failure mode of the test beam were observed with the help of Digital Image Correlation(DIC)technology.By analyzing the load-displacement curve,beam cross-sectional stress and rebar load-stress curve of the test beam,the effects of ECC layer height replacement rate,reinforcement ratio,mesh type,grid position and number of layers on the stress performance of the superimposed beam were studied.(3)According to the constitutive model obtained by the material property test,the bending process of the test beam was simulated,and the research variables were added on the basis of the test.(4)Based on constitutive model,flat section assumption and deformation coordination,the positive section stress-strain of CFRP-reinforced ECC-NC superimposed beam before cracking,cracking to yield stage and yield to failure stage were analyzed,and the calculation method of bending moment of each stage of superimposed beam was obtained,and the calculation formula of cracking bending moment,yield bending moment and ultimate bending moment was given.The conclusions reached are:(1)ECC-NC superimposed beam can effectively inhibit crack development,and arranging CFRP grid can further improve the control ability of test beam on cracks.(2)The influence of different parameters on the bending performance of the test beam is as follows: the ECC layer arranged in the compression area can improve the bearing capacity and ductility of the beam and increase the stiffness;Increasing the reinforcement ratio of longitudinal ribs can greatly improve the bearing capacity and stiffness of the superimposed beam.Among the three types of meshes,the CFRP grid has the best ductility,the BFRP grid makes the beam body have the largest number of cracks,and the strand grid improves the bearing capacity with the largest.Under certain premise,the closer the grid position is to the tensile zone,the more layers the grid,the more conducive it is to control the crack width and improve the stiffness of the beam body.(3)The numerical analysis results show that the constitutive model of the material constructed in this paper is more accurate,and the finite element analysis can accurately predict the crack development and failure form of the superimposed beam.(4)The theoretical analysis results show that the calculation formula of bending moment at different stages of the stacked beam derived in this paper is reliable,which lays a foundation for the theoretical analysis and engineering application of mesh-reinforced superimposed beam.