Long-term Mechanical Properties Of RC Beams Strengthened With Prestressed CFRP Under Natural Exposure

Since the reinforced concrete(RC)structure reinforced with prestressed carbon fiber reinforced composite(CFRP)can give full play to the high-strength characteristics of CFRP,change the stress distribution of the reinforced member and improve the strength of the entire member,pre-stressed CFRP reinforcement technology is more and more obtained Favored by technical personnel in the field of civil engineering and transportation construction.However,most of the prestressed CFRP reinforced RC structures are under natural exposure.The impact of natural exposure on the long-term mechanical properties of prestressed CFRP reinforced RC members is unknown,and there are few related studies.In this paper,the pre-stressed CFRP reinforced RC beams in the subtropical natural exposure environment are taken as research objects,and a theoretical model is established to analyze the long-term prestress loss of the reinforced component under natural exposure conditions and the bonding performance of the CFRP-concrete interface.The application of CFRP in actual engineering has certain value.The main research work and conclusions of this article are as follows:(1)Considering the effect of natural exposure conditions on the shrinkage and creep of concrete,a study was conducted on the long-term prestress loss of the reinforced beam.Compared with the previous experiment of this research group,the prestress loss rule proposed earlier was revised,and the revised theoretical results were in good agreement with the experimental results.(2)Aiming at the subtropical natural exposure environment,the CFRP-reinforced RC beams were subjected to natural exposure experiments and model analysis,and the bilinear bond stress-slip model at the CFRP-concrete interface at different exposure times was derived.By substituting the relationship between the CFRP-concrete interface affected by the environment into the CFRP-reinforced structure,the bond shear stress and the interface peeling load of the CFRP-concrete interface along the entire length of the bond length can be obtained.Through research,it is found that the prestressed CFRP reinforced RC beams affected by natural exposure have a great effect on the bonding behavior of theCFRP-concrete interface in the early stage of natural exposure,but are basically stable in the later stage.Among them,the maximum bond shear stress and stiffness are the most affected,and the maximum reductions are 31.9% and 36.8%,respectively.As the exposure time increases,the location of the maximum bonding shear stress tends to move backwards,indicating that natural exposure accelerates the damage to the interface behavior.(3)A natural exposure experiment platform was built,and 15 pre-stressed RC beams with a prestress levels of 22% and 15 non-prestressed RC beams were used as a control experiment,with 5 pre-stressed beams and 5 non-prestressed beams as a group The period of time is 1 year,2 years and 3 years of natural exposure.During the experiment,regularly monitor the stress,strain,displacement,temperature,humidity and salinity of the components.After the exposure period,a loading experiment is carried out to obtain data to improve the relevant theory.