Time Effect Analysis Of Continuous Rigid Frame Bridge Based On Shrinkage And Creep Model NCHRP496

The very common phenomenon of deflection and crack and the mutual coupling between them in midspan of long span prestressed concrete continuous rigid frame bridge at home and aboard which has operated many years will have serious impacts on the safety and practice performance of structures. The accuracy of calculation results rely on the choices of right analytical method and accurate prediction model of shrinkage and creep of concrete. Research shows the error of prediction model has more obvious influences on results than the error of analytical method. The widely used prediction models of shrinkage and creep of concrete which are fitting formulas based on a large amount of ordinary concrete long-term test are not accordance with the common used high strength concrete. In order to study the effects of prediction models of shrinkage and creep of high strength concrete on the calculation of loss prestress and camber in continuous rigid frame bridge, the two prediction models NCHRP 496 model and JTG D62-04 model are selected to execute the research object to Xue Jiaba 2# bridge.â‘ The widely used prediction models of shrinkage and creep of concrete and NCHRP 496 model based on high strength concrete test are systematically summed up. On the one hand, the influence of different nominal thickness of member and the differe nt strength of concrete on the predictive value of various models are mainly analyzed. On the other hand, the comparison predictive value between NCHRP 496 model and JTG D62-04 model as a result of the change of concrete strength are carried out;â‘¡The calculation method of aged stress redistribution of section considering the interaction of shrinkage and creep of concrete, relaxation of prestressed steel and nonprestressed steel based on the aged-adjusted effective modulus method are studied;â‘¢The author exploit the FEA program Midas/Civil to compare and analyze the difference of long-term prestress loss and vertical deflection between JTG D62-04 model and NCHRP 496 model, mainly based on the pratical engineering Xie Jiaba 2# bridge, and take the He Zhang grand bridge as auxiliary example to verify the validity and applicability of the analysis results.Research shows that the prediction model of JTG D62-04 is not able to accurately take the effect of high strength concrete into account. Not only the JTG D62-04 model has a risk of overestimating the characteristic of creep and underestimating the characteristic of shrinkage of the high strength concrete, but also does it underestimate the long-term prestress loss because of shrinkage and creep of concrete. Therefore, the JTG D62-04 model causes smal er setting camber and can explain the universa l phenomenon of excessive deformation of midspan of bridge to some extent. Thus, In order to analyze accurately the effects of shrinkage and creep of high strength concrete, the need that Chinese specification JTG D62-04 model should be revised and improved are suggested.