Research On Mechanical Properties Of Environmental Damage RC Beams Strengthened With CFRP

Due to the impact of various environmental effects, engineering construction quality problems and the increasing using time, the performance of buildings is gradually declining. Strengthening and repairing can not only ensure that damaged buildings are adapted to the development of human society, but also can save construction costs. However, there are some defects in existing strengthening methods.Carbon fiber reinforced polymer(CFRP) is widely used in building maintenance,which has many excellent performances, such as lightweight and high strength,corrosion and fatigue resistance. Therefore, the experimental and theoretical study on mechanical properties of environmental damage RC beams strengthened with CFRP is conducted, and the main contents of this paper are briefly summarized as following:The experimental study on mechanical properties of CFRP strengthened environmental damage beams is conducted.The effects of reinforcement ratio, CFRP strengthening ratio and environmental damage on flexural performances of CFRP strengthened beams such as failure mode, bearing capacity, deformation and crack are analyzed, the results show that the failure modes of the RC beams strengthened with CFRP can be classified into distinct categories: namely, tension failure of CFRP and CFRP debonding failure. With the increase of reinforcement ratio, the bearing capacity increases, the enhancement degree of bearing capacity is gradually decreased,the degradation speed of stiffness and the increment speed of section curvature decrease, the mid-span deflection, the crack width and the average crack spacing decrease. With the increase of strengthening ratio, the bearing capacity and the enhancement degree of bearing capacity increase, the degradation speed of stiffness and the increment speed of section curvature decrease, the mid-span deflection, the crack width and the average crack spacing decrease. With the increase of environmental damage degree, the bearing capacity and the enhancement degree of bearing capacity decrease, the degradation speed of stiffness and the increment speed of section curvature increase, the mid-span deflection increases, the crack width and the average crack spacing increase.The strain analysis shows that the strain distribution of cross-section is consistent with the assumption of plane section. In initial, the trend of CFRP strain’s growth is consistent with steel strain. The rate of CFRP strain’s growth is gradually larger than steel strain and CFRP is gradually taking the main tensile stress after yielding. With the increase of reinforcement ratio and strengthening ratio, the increment speed ofsteel and CFRP strain decrease. With the increase of environmental damage degree,the increment speed of steel and CFRP strain increase. The strain of U-shaped CFRP anchor continued to grow from the beginning to the end. The U-shaped CFRP anchor can prevent CFRP from debonding.According to static equilibrium and strain relation of cross section, theoretical formulas, considering the influence of reinforcement ratio, strengthening ratio and environmental damage degree, are deduced to predict the flexural strength of beams based on the experimental study. In addition, the design method for flexural strength is given.Considering the influence of reinforcement ratio, strengthening ratio and environmental damage degree, the CFRP strengthening ratio coefficient and environmental damage coefficient are introduced. The calculation methods for crack width and average crack spacing based on bond-slip model of ordinary reinforcement concrete beam are deduced.According to curvature method, considering the influence of strengthening ratio and environmental damage degree, the CFRP strengthening ratio coefficient and environmental damage coefficient are introduced. The calculation formula of deflection is deduced. In addition, a method to predict the deformation of beams is given. Meanwhile, the calculation formula of U-shaped CFRP anchor’s width is also deduced to ensure the effect of reinforcement.