A Study On The Fatigue Behavior Of CFL Strengthened RC Beam Under Variable Amplitude Loading

With the progress of technology and the upgrading of industrial structure, highwaytransportation is playing a more and more important role in our society. But under thetemptation of huge market profits, overload phenomenon is existed in most of the freight cars,and some loads of vehicles are much heavier than the design bearing load of Highway Bridge,which caused pavement damage, bridge fracture and greatly reduce of Normal service life. Toensure the safety of the bridge structure and transportation, we must do the reinforcement andmaintenance for these bridges. Therefore, analysis the bridge structure damage caused byoverloading vehicles has important practical significance for the relevant prevention andmaintenance measures.This paper uses the Carbon Fiber Laminate which was developed by our research teamand combine the actual service loading conditions of the bridge，we studied the fatigueperformance of CFL strengthened RC beams under the large loads(overloads) byexperimental study and theoretical analysis method. The main contents and conclusions areshown as follow:1) Firstly, we get the flexural capacity of normal section and the overload limits of thesimply supported beam in real bridge through theoretical calculation. Then determine fivetypical car models by deal with the survey data of highway, and calculating the maximumamount bending impact generated by every car, take the influences that beyond the overloadlimits out and compiling the load spectrum with3amplitude levels. At last translated the loadspectrum into another load spectrum also with3amplitude levels which is suitable for theMTS experimental system.2) The Smax-N curves of extreme fatigue lives are obtained by analyzing the fatiguetesting results of3-point bending RC beams strengthened with CFL under overloading loads.Moreover, the fatigue strength of extreme fatigue lives is established as about0.62Pu. Thencompared the S-N curve to the constant amplitude fatigue and random fatigue S-N curve, theresults shows: the fatigue life of RC beam under constant amplitude is longer than the life under variable amplitude loading; and the fatigue life under random load is obviously shortthan life under variable amplitude loading when at the same amplitude.3) Discussing the evolvement rule of midspan-deflection of the reinforced beam andobtained the expression of midspan-deflection with the fatigue life. And it is concluded thatthe increase of load mainly make the deflection of reinforced beam increases at the beginningwithin a limited circulation. The midspan-deflection growth rate does not increasesignificantly with the increasing of loads，4) After entered the stage of ductility, stiffness decay rate increases with load levels.And compared to the constant amplitude fatigue in the elastic stage, the stiffness decay rate isbetween1.5to2times bigger.5) Combined with the test data, we predicted the fatigue life of reinforced beam undervariable amplitude loads based on Miner rule and Corten-Dolan cumulative damage theory.The results shows the prediction accuracy is good and can meet the engineering requirementswhen D=0.77and d=7.9.