| Setting the RC bridges serving in subtropical coastal area are as the research object,considering the seawater environment and climate change of southern areas and coastal areas in China and the actual working condition for load-bearring structures of the serving bridges,a RC structure strengthened by carbon fiber laminate(CFL)was constructed in this study.The fatigue experimental method under coupling action of hot-seawater environment and cyclic loads was proposed and a hot-seawater environment simulating and controlling system was developed.Then,the mechanism of erosion by Chlorine ion to CFL reinforced RC structure was studied,and the environmental fatigue performance/durability of CFL reinforced RC structure under hot-seawater environment and cyclic loads coupled action was investigated.The main research contents and conclusions are as followings:1)Development of hot-seawater environment simulating and controlling system.In order to simulate the working condition of the RC bridges serving in subtropical coastal area,a fatigue experimental method under hot-seawater environment and load coupled action was proposed to establish an experimental platform of complex environment and load coupled action.In this study,the principle of an intelligent environment simulating and controlling system was established based on the rules of the salinity distribution near several main estuaries of Zhujiang River and the hot temperature of the actual working condition for bridges serving in this area.Then,an intelligent environmental simulating and controlling system that could be used with the improved MTS810 experimental system was designed.This system successfully passed the test conducted by third party institution.By performing test run and passing the test conducted by third party institution,the advanced technical standard of this system would be able to satisfy each design function.2)Investigation of erosion mechanism of Chlorine ion to CFL reinforced RC structures.Based on with or without reinforcement by CFL and different width of preset cracks,RC specimens and RC specimens strengthened by CFL with cracks were prepared.Then,the neutral salt spray tests were carried out;the specimens were divided in to different groups based on different salt spray concentrations(5%,6.6% and 13.2%)and pretreatment times(0d.10 d,20d,30 d,40d,50 d and 60d).The speed of erosion by Chlorine ion in different salt spray concentration and with different width of cracks,and the influence to specimens failure mode and ultimate bearing capacity were studied.A Chlorine ion dispersion model was also established.The study results showed that: 1)for CFL reinforced RC specimen,the Chlorine ion can only reach to surface of concrete after 50 d with salty spray pretreatment.CFL reinforced layer could effectively prevent erosion by Chlorine ion;2)prevention of Chlorine ion erosion by CFL reinforced layer was more effective when the width of crack was under 0.6mm;3)when the salt spray pretreatment time was relatively short,the failure mode of specimens was in bending failure whereas when the pretreatment time was long,specimens failed in shear failure mode;4)dispersion equations of chlorine before and after CFL reinforcement to RC specimens were effective and feasible.3)Environmental fatigue experiments under hot-seawater environment and load coupled action.First,the actual working environments of serving bridges in coastal area of Guangdong province were simulated,and using own experimental platform,the fatigue experimental method of the load-bearring structures of bridge under hot-seawater environment and load coupled action was established.Then,5 groups of hot-seawater environments were set and there were 3-4 loading levels in each group.The environmental fatigue experiments of CFL reinforced RC under hot-seawater environment and cyclic load coupled action were successfully carried out.The study results showed that: 1)under constant temperature and salt spray concentration,the intelligent environment simulation and control system have reached technical standard,which was required when designing;2)the failure mode of CFL reinforced RC beams under hot-seawater environment and load coupled action was bending failure.Its failure process could be predicted as: concrete open crack ? erosion of tensile bar ? CFL debonding ? failure of specimen.This clearly showed that the anti-erosion performance of tensile bar was critical factor influencing the fatigue performance of CFL reinforced RC beams under hot-seawater environment and load coupled action.4)Fatigue performance of CFL reinforced RC beams under hot-seawater environment and load coupled action.Based on the results of environmental fatigue experiments and theoretical analysis,the influence mechanism of salt spray environment to the fatigue damage of the reinforced bridge stuctures was studied.Then the environmental fatigue equation of CFL reinforced RC beams under hot-seawater environment and load coupled action was established,and the prediction method of fatigue lives and fatigue limits of the RC beams strengthened with CFRP under hot-seawater environment and load coupled action was developed.The study results showed that: 1)the influence of erosion by Chlorine ion to the fatigue lives and durability of the strengthened RC beams was obvious.As concentration of Chlorine ion increased,fatigue lives and fatigue limits of the strengthened RC beams decreased.Fatigue life of the strengthened RC beams in hot-seawater environment(50?,5% salinity)was by 6.2% lower than in hot-wet environment(50?,95% R.H),and was by 25% lower than in atmospheric environment;2)the preliminary experimental results showed that the environmental fatigue equation of the strengthened RC beams established in this study under hot-seawater environment and load coupled action was effective and feasible.By using such environmental fatigue equation,the fatigue lives and fatigue limits of the RC beams strengthened with CFRP under hot-seawater environment and cyclic load coupled action could be easily and accurately predicted. |
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