Study On Mechanical Behavior Of Large-span Prestressed Concrete Continuous Girder Bridges Based On Cracking Damage

With the project of “The Twelfth Five Years” being carried out in China, thefoundation of transport infrastructure becomes slower comparing to the rapid pace ofdevelopment in the first decade. However, it is still be at the stage of fast development andgradual perfection in a considerable period of time. During the past few decades, theprestressed concrete grider bridge has got vigorously development and construction indomestic in that its spanning capacity and good performance of the use phase. Part of thebeam bridges appear beam cracking and cross scratching and other damages with thegrowth of the hours in operation. Such damages reduce the performance of the use ofprestressed concrete beams. How to make a scientific and effective assessment for thebridge by the changes of these mechanical properties. It is always a concern and a hot issuein bridge engineering community. Only finding out good solutions to these problems, can itdrives the infrastructure of bridge of China to a better,faster health development.This paper first shows the research status of the cracking of long-span continuousprestressed concrete bridge at home and abroad.This paper makes an accurate analysisabout mechanical properties under the influence of the effects that three cross-continuousprestressed concrete box girder bridge change in the concrete creep, the loss of prestress,andthe effect of temperature and the live load effect. All those base on some certaincircumstances. There are the calculation example of a three-span continuous prestressedconcrete box girder bridge, to crate the model of the full-bridge by adopting largegeneral-purpose finite element software ANSYS, to take full account of box beam spatialeffects and material nonlinearity. In order to find the main reason of the cracking damageand under torsion caused by large-span prestressed concrete by large-span prestressedconcrete continuous box girder bridges. I analyze the variation of mechanical properties ofthe bridge, and the statement of the deflection and stress changes which influenced by thefactors of main beam above.By calculating the analytical results, that the loss of prestress and live load (especiallyoverload) effects is the main reason for the long-span continuous girder bridge cracks andcross-sustained under flexible, when the30%loss of prestress, midspan section appearing 3.300MPa tensile stress, the cross section has been cracking section stiffness reductionfactor is0.865; when applied to four times the live load, cross-section appearing4.670MPatensile stress, the cross section has been cracking section stiffness reduction factor of0.832;and concrete creep and temperature effects in the calculation of the midspan section bottomedge of the tensile stress, but did not exceed the tensile strength of concrete value, so thecracks, but two factors could cause the bridge under torsion and cracking, is also one of thefactors. Under the role of combination effects consider the dead load, live load, prestressedload (considering10%of the prestress loss) plus heating up the temperature gradient effect,and10years of shrinkage and creep,the main beam cross cross-section tensile stressexceeds the tensile strength of concrete value, cross-section bottom edge cracks,cross-section stiffness reduction factor of0.918, it is clear these negative factorscombinedaccelerate a bridge to cross in the lower torsion beam cracks generated.