Numerical Analysis Of Mechanical Behavior Of FRP Strengthened RC Beams Based On Cohesive Zone Model

The FRP-strengthened reinforced concrete structure has been widely used in civil engineering because of its advantages of corrosion resistance,simple construction,and almost no change in the original size of the structure.Due to the limitation of scale and cost,the experimental research on the FRP strengthened of the frame structure is usually replaced by the experimental study of the bearing capacity and deformation capacity of the FRP strengthened beam-column sub-structure.In order to provide design basis for engineering application of FRP strengthened RC frame structure,based on the existing FRP strengthened reinforced concrete beam-column sub-structure test,numerical simulation analysis was carried out in this paper.First,based on the analysis of the basic theory of the cohesive zone model,the finite element analysis of the single shear test data is fitted to determine the values of the three key parameters of the bilinear cohesive zone model.The bilinear cohesive interface element is established.The debonding failure of FRP-concrete interface is considered by using the bilinear cohesive interface element,the nonlinear properties of concrete and steel bar during loading are considered at the same time.Numerical simulation of ultimate bearing capacity of reinforced concrete beam-column sub-structure strengthened with FRP is carried out,the influence of FRP strengthening on ultimate bearing capacity,stiffness and ductility of beam-column sub-structure and the peeling off process of the bond interface are discussed.According to the stress characteristics of the reinforced beam-column sub-structure under failure,an improved form of FRP strengthened beam-column sub-structure is proposed.Secondly,based on the conclusion of finite element analysis and experimental analysis of FRP strengthened RC beam-column sub-structure,simplified calculation of reinforced concrete structures strengthened with FRP is carried out by using truss model theory.Based on the equilibrium condition of the average stress,the strain Mohr circle condition and the modified pressure field theory,a method for establishing a simplified truss analysis model of FRP strengthened concrete structures is proposed,the mechanical characteristics and transfer mechanism of the structure are discussed using the simplified truss analysis model.Finally,the theoretical analysis of the stress-strain distribution of the beam sections of the FRP strengthened concrete structures before and after the yielding of steel bars was carried out.The method of numerical regression was used to derive the non-uniform strain coefficient of FRP and steel bars and the composite coefficient of deformation of concrete,the calculation formulas and deformation formulas for bending stiffness of reinforced concrete beams strengthened with FRP before and after yielding are obtained finally.The test data of specimens with different beam sections,reinforcement ratios,reinforcement materials and reinforceme nt amounts were collected and analyzed to verify the calculation formulas and deformations presented in this paper.In this paper,combined with finite element numerical simulation analysis and existing experimental results,the influence of FRP reinforcement on the mechanical behavior and force transfer mechanism of the beam-column structure is analyzed.A more economical and reasonable strengthening method of beam-column sub-structure is presented.The simplified truss analysis model of reinforced concret e beams strengthened with FRP and the formula for calculating the equivalent bending stiffness before and after the yield of longitudinal reinforcement are proposed for simplified calculation,which provides some reference for the practical engineering app lication of FRP reinforcement.