The Forecast Of Remaining Service Life For Prestressed Concrete Bridge

Prestressed concrete girder bridge is one of the most common bridge type inbridge engineering. Because of the defects and deficiencies in the building materialsand the load effect and the natural environment erosion that bore by the bridge in thebridge using procedure, the bridge structural performance will decay, which will leadsto the result that the durability and the bearing capacity of the bridge becomeinsufficient. The service life research of prestressed concrete girder bridge canprovide basis for the decision of the bridge maintenance, which has importantpractical value and theoretical significance. This text treat the subordinate line bridgeof the south-to-north water diversion bridge of Hanghailu connecting line ofZhengshao express way as engineering project, which will be called as thesubordinate line bridge for short in the text. This article studied the factors that makethe resistance of prestressed concrete girder bridge declining and forecast the residualservice life and finished the works as follows.1.The factors that make the resistance of prestressed concrete bridge and that ofconcrete bridge declining is discussed. The concrete carbonation prediction modeland reinforcement corrosion prediction model and concrete strength change modelsand resistance attenuation model that based on the structure of the steel bar corrosionare all chose in the article.2.The statistical analysis technique of bridge dead load in the norms and themaximum vehicle load effects in design reference period and assessment referenceperiod are discussed,so as the load distribution models and the parameter estimations.At last, the computing method of vehicle impact load effect and the statistical lawcrowd load are given in the article.3.The criterion to judge the end of bridge carbonation life and the corrosivecracking life and carrying capacity of life is studied, which provide basis to judge theresidual service life of bridge. The limit state equation of carbonation life ofprestressed concrete girder bridges and the corrosive cracking life of prestressedconcrete girder bridges and flexural carrying capacity life of prestressed concrete girder bridges are built, the reliability indexes of every service life can be computedaccording to this.4.Based on time-varying reliability theory, concrete carbonation life of thesubordinate line bridge girder and pier and the corrosive cracking life of thesubordinate line bridge girder and pier are computed, the flexural bearing capacityreliability index of the main girder across and the shear bearing capacity reliabilityindex of1/4span of the main girder across in the design reference period are given too.The results shows that a prestressed concrete bridge which is in general atmosphericenvironment, the concrete carbonation processes and the corrosion processes ofprestressed reinforcement rust ana rebars will be very slow. Only the prestressing lossand changes of concrete strength should be considered in attenuation of carryingcapacity. The bending bearing capacity of prestressed concrete girder bridge in designreference period can be guaranteed in this situation. Only considering steel corrosioncaused by carbonation，The shear calculation results of subordinate line bridge showthat the shear carrying capacity of subordinate line bridge can meet the requirementsin the design reference period.