Method Study On Residual Fatigue Life For Existing Urban Concrete Simple-supported Beam Bridge

Most of the Bridges in China are reinforced concrete girder Bridges,most of which have been in operation for decades.During the operation period,the Bridges mainly bear the ever-changing load of operating vehicles,in addition to the influence of external environment and the deterioration of their own materials.With the increase of traffic load,the degree of vehicle congestion is becoming more and more serious,which brings different degrees of damage to the bridge structure.The internal damage of the structure keeps accumulating,and finally leads to the fatigue failure of the bridge.In order to analyze the influence of operating vehicle load on the residual fatigue life of existing urban Bridges,this paper mainly carries out the following research work:(1)The bending fatigue properties of steel bars,prestressed steel bars and Bridges are summarized and sorted.(2)The vehicle data were collected through the traffic survey of several cities’ main roads,and the proportion of various models,axle load proportion and vehicle weight were statistically analyzed.Combined with the urban load limit policy,a vehicle load model which is consistent with the current situation of vehicle load in urban operation is constructed.The Monte Carlo method is used to simulate the random traffic flow.Through the influence line loading,the time-history distribution curve of bending moment in the mid-span section of a typical girder bridge is calculated to obtain the fatigue stress spectrum of the steel bar in the most adverse section.(3)Based on the S-N curve equation of reinforcement and steel wire,the Miner linear cumulative damage criterion and the Corten-Dolan cumulative damage criterion,the residual life prediction of urban typical concrete girder Bridges was carried out.(4)Combined with the static and dynamic load test index of typical girder bridge,the actual stiffness of the bridge is calculated.Based on the actual stiffness and stiffness degradation damage law,the residual life of typical girder bridge with stiffness degradation under normal service condition is predicted.(5)The influence of different corrosion rates of steel bars and the increase of traffic volume on the residual fatigue life of typical Bridges is discussed.