Effect Of Temperature On Fatigue Performance Of RC Beams Strengthened With CFL Under Random Loads

In the recent years, the fiber reinforced polymer (FRP) strengthening technology hasbeen more and more widely used in bridge engineering. Because the bridge structure exposedto the natural environment, the annual temperature and sunshine temperature differenceeffects were significant. And the RC beams strengthened with FRP was composed of a varietyof materials，and there were significant difference in thermal expansion coefficients andvariations of material properties with temperature of the constituent materials. Therefore,fatigue performance and durability of RC beams strengthened with FRP should be consideredthe impact of ambient temperature. In addition, there’s a big difference between the fatigueproperties of RC component strengthened with FRP under the random load and the constantamplitude load. While the real vehicle load of the bridge has a randomness in value, spacelocation and time. Therefore, it has important scientific significance and application value tocarry out research on the fatigue properties of FRP reinforced RC beams in the environmenttemperature and the random load coupling/interaction.Based on the RC bridge strengthened with carbon fiber laminate (CFL) as the researchobject, under4different environment temperatures and3different load levels, the fatigueperformance of RC beams strengthened with CFL were discussed in the interaction ofenvironment temperature and random load. The main research contents and conclusions areshown as follows:（1）The time-varying characteristics of the vehicles spacing based on the vehicleloading data which was collected through the weigh-in-motion system installed on the certainsection of Guangzhou highway were analyzed. The data contained the lane, motorcycle type,axle load, total weigh, velocity and the time of the car transit. According to the analysisresults, the effect of vehicle load that forces on the bridge was simplified. Considering theprinciple of load transverse distribution, and converting the three dimensional problem intoplane, then the stress-time process of bending moment in the span of the bridge were obtained.By using the data, a simulation method of random loading series on highway bridge wasproposed, and a random loading series for random fatigue tests (experimental series) wascompiled. Comparing to the simulation method of highway bridge vehicle loading series usedin the past, by adopting the random loading series simulated and complied in this paper iscloser to the actual working condition of the bridge.（2） A fatigue test method for RC beam strengthened with CFL under thecoupling/interaction of environmental temperature and random vehicle load has been proposed according to the natural climate characteristics in Guangdong Province and theactual traffic load of the bridge. Three point bending fatigue test has been carried outsuccessfully under temperature-random load. The experimental results show that, the mainfatigue failure mode of RC beam strengthened with CFL is interfacial peeling between CFLand concrete; the fatigue performance was significantly affected by ambient temperature, thefatigue life decreases with increasing temperature in the same load level, and with the increaseof load level, the decrease amplitude increases. However, the effect of the fatigue limit oftemperature change on the strengthened beams is not significant.（3）A semi-empirical formula of the fatigue life of RC beam strengthened with CFLunder the coupling/interaction of environmental temperature and random load is presentedbase on theoretical analysis and statistical analysis of experimental data. The validity of theformula is preliminarily verified through experiments under different temperatureenvironments. The results show this formula can be used to predict the fatigue life and thefatigue limit of the RC beams strengthened with CFL under coupling/interaction ofenvironmental temperature and random load, and can guide the bridge fatigue/durabilityreinforcement design.（4）The fatigue cumulative damage rule has been analyzed. The results show that thelinear cumulative damage rule (Miner rule) can be not apply to fatigue damage evolution ofstrengthened RC beams under temperature-random load coupling within scope of this paper.Therefore, a modified cumulative damage model was proposed, and the results show that themodel is effective and feasible. Using the model, the fatigue lives of RC beams strengthenedwith CFL under temperature-random load coupling can be predicted easily and reliably.（5）An equation of mid-span deflection curves of RC beams strengthened with CFLunder temperature-random load coupling/interaction has been proposed based on thediscussion of effects of ambient temperature and load level. And the validity of the equationwas preliminarily verified through verification experiments. The verification results show thatthe prediction for mid-span deflection values of strengthened beams was comparativelyaccurate, but the prediction for parameters of the deflection equation had larger errors. On thebasis of the deflection curve equation, a fatigue life prediction equation of strengthened beamswas proposed. Calculation results of verification beam (calculation example) show that, usinga very small amount of load cycles and deflection data, the fatigue life of the RC beamstrengthened with CFL can be predicted with higher accuracy.