Study On New Methods For Strengthening Concrete Beams With Anchored CFRP Reinforcement

At around the 1980 s,developed countries such as Switzerland and the United States began to apply CFRP to building reinforcement,and then at the beginning of this century,China also began research on CFRP reinforcement technology.Nowadays,externally bonded(EB)technology and near-surface mounted(NSM)technology are two major methods which are widely used worldwide in the field of building reinforcement.EB technology is used for flexural strengthening by pasting fiber sheets to the tension surface of beams.However,EB CFRP system relies exclusively on the cohesive strength of epoxy resin to transfer load,so CFRP can only develop 40%-50% of ultimate tensile strength when debonding failure occurs.That is a waste of material properties.NSM technology is to embed CFRP bars into the grooves cut in the tensile surface of the beam,then fill the grooves with epoxy for reinforcement.Compared with EB CFRP system,NSM CFRP system requires less preparation work and can protect the CFRP reinforcement system better.However,premature debonding limits the development of CFRP tensile strength,and the liquid property of epoxy resin limits the scope of application.Anchored EB CFRP system can fully develop tensile strength of CFRP,but the fabrication of CFRP anchors is relatively complicated.There is still much room for improvement in terms of construction simplicity.This paper proposes two new methods for strengthening concrete beams with anchored CFRP reinforcement that can efficiently utilize the properties of CFRP materials while being relatively simple to construct.The experiments verified the feasibility of the two methods and evaluated the influence of different parameters on the reinforcement effect.This paper contains two parts of experiments.The study contents of this paper are as follows:The first part proposes a new anchored NSM method for strengthening concrete beams.In this method,instead of using commercial CFRP bars which is hard to bendfor anchorage,plastic CFRP bars folded by CFRP fabric are bent into pre-drilled holes on the beam to make anchor.The experiments contain 30 tests and evaluate the influence of strengthening type(anchored or anchor-free)on reinforcement performance from four aspects: ultimate loads,failure modes,degree of CFRP material performance and load-deflection curve.Moreover,the amount of epoxy,quantity and location of grooves are also studied as parameters.The experiments demonstrate that new anchored NSM CFRP system is able to adequately develop the tensile strength of CFRP reinforcement with less epoxy than NSM technology and indicate a great potential to apply this system to positive moment regions.Based on the first part,the second part of experiments simplify the construction of cutting grooves of anchored NSM technology and propose a new anchored EB technology for strengthening concrete beams.However,experiments show that the reinforcement performance will be unstable without grooves.In order to solve this problem,CFRP patches are used in the experiments.CFRP patch arrangement,embedment depth and reinforcement section are studied in this part as parameters.Experiments demonstrate that the proposed anchored EB CFRP system has a much simpler construction step than anchored NSM CFRP system while ensuring the efficient use of CFRP material properties,and further reduces the amount of epoxy resin used.