Flexural Property Of Concrete Beam Strengthened With High Performance Cement-based Composite And Prestressed CFRP Grid

Fiber-reinforced plastic(FRP)has been widely used to strengthen concrete structures due to the simple construction technology,low cost,and good reinforcing efficiency.The most common strengthening method is external bonding of FRP sheets or plates with epoxy adhesive on the concrete members;however,there are still some issues to be addressed,such as lower utilization of FRP strength,lower resitance of epoxy adhesive under high temperature or subjected to the fire,and aging and poor durability of adhesive under high humidity or freeze-thaw environments.Therefore,a new strengthening system was developed in this study using prestressed carbon fiber grid and high-performance cement-based composite(ECC)to solve the above issues in tranditional strengthening method of external bonding of FRP with epoxy adhesive on the concrete members.The main contents of this study includes:(1)A tensioning set-up was designed to apply prestress to the CFRP grid.Then,the prestressed CFRP grid and ECC were both used to strengthen the reinforced concrete(RC)beams.On the basis of the experimental study,the influence of test variables(different prestressing levels,different reinforcing numbers of grid layers)on the strengthening efficiency was compared and analyzed in terms of the failure partten,load-deflection curve,concrete strain,and CFRP grid and steel bar tensile strain.(2)A numerical analysis model was established using DIANA finite element software.The mechanical properties of strengthened RC beams was analyzed considering the bond slip between the interface of ECC and CFRP grid and without considering the bond slip.Through the comparison of numerical and experimental results,the reliability of numerical method was validated,and carry out parameter sensitivity analysis for different prestress degrees.(3)The failure modes and failure mechanism of strengthened beams were classified and discussed,and then a theoretical model was established to predict the performance of RC beam strengthened by ECC and prestressed CFRP grid.On the basis of the test results,the calculated formula for bending capacity of beams with the failure modes of interface peeling and CFRP grid fracture were especially proposed and discussed.(4)The comparison between test data and mumerical results shows that the composite strengthening system developed in this study is effective to improve the bending property of RC beam.Compared with the control beam and the beam strengthened by ECC and non-prestressed CFRP grid,the deformation in the middle span of the beam strengthened by ECC and prestressed CFRP grid can be controlled to a certain extent,the cracking load can be enhanced certainly,and the ultimate bearing capacity can be significantly improved.