Research On Fatigue Design Method Of Concrete Flexural Members With Externally-boned FRP

In recent years, due to the sharp increase of transport volume and the continuously improve of crane level, some old roads, railway bridges and concrete crane girders are bearing a repeated higher level of stress. The probability of fatigue failure is greatly increasing. The fatigue reinforcement has become an important way to increase the fatigue life of these concrete beams. But the researches on anti-fatigue properties of FRP-reinforced concrete structures are still very limited. In addition, the study of fatigue behavior of FRP-concrete interface is lacking. The clear fatigue design method for FRP- reinforced concrete structures has not been proposed so far. In this background, a research on fatigue design method of concrete flexural members with externally-boned FRP was conducted based on the fatigue tests of FRP-concrete interface and fatigue tests of two damaged FRP-reinforced beams. The main contents and results are as follows:(1) Nine kinds of fatigue failure modes were summarized based on the existing research results at home and abroad. Then the design principles of fatigue reinforcement were put forward based on the failure mechanism of RC beams strengthened with FRP sheets.(2) The evolution of CFRP strains and interfacial shear stress was studied based on the results of fatigue tests on CFRP-concrete interface. Using beam specimens, the fatigue properties of CFRP-concrete interface were analyzed considering five variables, namely, the load level, concrete strength, CFRP sheet-to-concrete width ratio, bond length and cyclic loading frequency. Finally, a debonding load limit which can be used for the fatigue design of FRP-concrete interface was proposed.(3) The flexural fatigue failure and shear fatigue failure of FRP- reinforced concrete beams were studied. Then the checking method was proposed for fatigue stress in cross section and oblique section material of FRP- reinforced concrete beams.