Study On Time-varying Reliability Of Reinforced Concrete Bridges Strengthened With Intelligent CFRP Plates

Under the influence of design,construction,operating environment,load and other factors,the bearing capacity of the bridge will decrease during the service,so it is not suitable for normal use.In order to meet the requirements of continuous bridge service,it is very important to repair and reinforce the bridge.Carbon fiber sheet has its unique advantages in performance.The use of carbon fiber sheet to reinforce reinforced concrete bridge structures has been increasingly widely used.When evaluating the time-varying reliability of reinforced Bridges,the influence of time-varying properties of structural materials on the structural resistance and the influence of changing vehicle flow on the structural load effect should be considered.In the previous time-varying reliability evaluation methods,the time-varying properties of structural materials generally only consider the influence of the environment on the strength of materials,and do not consider the influence of load on the strength of materials.The relevant statistical parameters of the load effect are generally calculated according to the standard values or the corresponding calculation model.It can’t accurately reflect the real situation of the bridge load in the process of use.These factors will affect the time-varying reliability evaluation of the reinforced bridge.It is necessary to carry out further research on the above problems.The main research contents of this paper are as follows:(1)Apply fiber grating sensing technology to reinforcement materials.The fiber grating sensor is embedded on the carbon fiber board to make an intelligent CFRP plates(CFRP-OFBG)with self-monitoring performance.Reinforced concrete beams with intelligent CFRP plates,and experimental research on reinforced beams.The test results show that: After the test beam is strengthened,the ultimate bearing capacity and fatigue performance are significantly improved.The main reason of fatigue failure of reinforced beam is fatigue fracture of steel bar.Fatigue loading will reduce the ultimate bearing capacity of reinforced beams.(2)Combine the test data and corresponding calculation model.Through the method of data fitting and formula derivation,analyze the time-varying strength change law of concrete,steel bar and CFRP board.Consider the effects of natural environment erosion and fatigue loading on the time-varying strength of the material,and it will be integrated into the calculation of the time-varying resistance of the reinforced beam.(3)According to the theory of flat section hypothesis,the calculation method of the load effect of the reinforced beam based on the monitoring data of intelligent CFRP plates is derived.The calculated results agree well with the experimental values.On this basis,combined with the time-varying model of material strength,the calculation method of the load effect of the reinforced beam considering the time-varying strength of the structural material is derived.(4)The JC method is used to calculate the time-varying reliability index of the reinforced beam with or without considering the influence of fatigue load on the structure resistance.Calculations proves that: Without considering the effect of fatigue load on the time-varying strength of structural materials,the time-varying reliability index shows a gentle downward trend.When considering the effect of fatigue load on the time-varying strength of structural materials,the rate of decline of the time-varying reliability index increases significantly in the middle and later years of service life.It shows that the fatigue load has a significant effect on the time-varying reliability index of the reinforced beam in the middle and late stages.In the calculation of time-varying reliability of reinforced bridges,the effect of fatigue load on the time-varying strength of structural materials should be considered.Based on the above research,according to the load value calculated by the measured data of the intelligent CFRP board,the real-time load effect of the reinforced bridge is statistically calculated.The time-varying reliability index of the reinforced bridge can be calculated through the monitoring data of the intelligent CFRP board.