Study On Fatigue Performance Of RC Beams Strengthened With CFL Under Hot-wet Environments

Real service environment has a significant influence on fatigue and durability behavior of the members since the main reinforced concrete(RC)structural members of bridges are served under vehicle loads and environment coupling action.However,environment and loads were considered separately(uncoupling)in traditional durability experiments.This was different from the real service conditions of the main structural members of bridge.Therefore,it is necessary to discover the effect mechanism on fatigue and durability behavior of RC members strengthened with carbon fiber reinforced polymer(CFRP)under environment and fatigue load coupling and uncoupling action.In this paper,a new type of FRP sheet called "carbon fiber laminate(CFL)" was used to strengthened the RC beam.Taking this as the research object and by combining experiment with theoretical analysis,the fatigue and durability behavior of RC beams strengthened with CFL under hot-wet environment was studied.The main research contents and conclusions are as follows:1)In order to simulate real service conditions of bridge structures in subtropical area,hot-wet environment simulation and control device(Type SDH4036L)capable of supporting MTS810 test system was produced,which was designed by this research group.This system was used to test the CFL strengthened RC beams under hot-wet environment and fatigue load uncoupling action,the coupling action and the hot-wet cycle environment and fatigue load coupling action.2)Ten CFL environment RC beams was tested under three point bending fatigue loads with uncoupled high temperature and humidity environment(Group A:50?,95% R.H).The result showed that the fatigue limit of strengthened beam under high temperature and humidity environment was 85% of that under room temperature.And the decaying rate of strengthened beam's secant stiffness under high temperature and humidity environment was about 65% of that under room temperature.3)Twenty CFL strengthened RC beams set into two groups was tested under three point bending fatigue loads with coupled hot-wet environment(Group B:50?,95% R.H;Group C:50?,85% R.H).The result showed that experiment method significantly influenced the environmental fatigue behavior of RC beams strengthened with CFL.Compared with test results using traditional method of environment and load uncoupling action,hot-wet environment and load coupling action decreased the fatigue life of strengthened beam.For test results in high temperature and humidity environment(50?,95% R.H),fatigue limit under coupling action(Group B)was reduced 20% of Group A's.And the load level was higher,the descend range of fatigue life was greater.In the same temperature,the humidity was higher,the fatigue life was lower.Compare with the test result of Group C,the environmental fatigue limit was reduced by 20%.4)Nine CFL strengthened RC beams was tested under three point bending fatigue loads with coupled hot-wet cycle environment to simulate the variation law of hot-wet environment of bridges in Guangdong region.Compare with the test result of room temperature,the study showed that the fatigue limit of CFL strengthened RC beams under hot-wet cycle environment was reduced by 26%.The reason was that the hot-wet stress was produced in the interface between the CFL and concrete under hot-wet cycle environment.And the theoretical analysis results of the hot-wet stress in the interface basically proves the conclusion.5)For the fatigue life prediction of the RC beams strengthened with CFL under the hot-wet environment and fatigue load uncoupled action,this paper proposed a prediction method based on the propagation rate of fatigue main crack.By proposing a J-integral calculation method of fatigue main crack considered the variation of material performance and the influence of environment,and implementing a fatigue main crack propagation experiment,an expression of fatigue main crack propagation rate was developed.The environment fatigue life of strengthened beams was predicted accurately by using the expression.6)By theoretical analysis and experiment study,the fatigue equation of strengthened beams under hot-wet environment and load coupled action was established and get the preliminary validation.The fatigue life and the fatigue limit of strengthened beams under hot-wet environment and load coupled action could be predicted conveniently and accurately by using the equation.