Analysis Of Creep And Shrinkage Effects In High Strength Concrete Box Girder Bridge

With the development of height and span of the bridges and the enrichment ofbridge loading, an increasing number of high strength concrete (HSC) have beenapplied to the long-span pre-stressed concrete box girder bridges. With thecharacteristics of high strength, low water-cement ratio, intense compactness and so on,made high strength concrete possessing a different shrinkage and creep properties fromordinary concrete. For bridges are in the natural environment, there is a certain degreeof randomness with the box girder concrete material properties, the environmentalsituation and the loading on structures, also, influence factors of shrinkage and creep arecomplicated, and thus, which make it difficult to accurately forecast and control ofcreep and shrinkage effects on structures.Accuracy analysis of shrinkage and creep effects of long-span pre-stressedconcrete box girder bridges is generally dependent on the selection and application ofprediction model of creep coefficient and shrinkage strain and analysis method ofshrinkage and creep effects. Therefore, the investigations on the effects of high strengthconcrete bridge shrinkage and creep are carried out in this dissertation from above twosides, summarized as follows:(1) Based on the age-adjusted effective modulus method, a creep strainincremental recurrence formulas about HSC creep and the stress relaxation factorfunction were deduced according to the revised creep prediction model on HSC; Withthe secondary development function of the finite element software ANSYS, an approachto adjust the characteristics of elasticity modulus of concrete was proposed and thesubroutine USERCR.F and USERMAT.F have been developed secondary. Finally,according to the incremental recurrence formulas, an ANSYS model of continuousrigid-frame bridge has been analyzed, which demonstrated the rationality of the compilemethod and is helpful to provide a reference for the creep behavior analysis of HSCbridges with other prediction models.(2) The influence of size effect of member on shrinkage and creep developmentwas preliminarily discussed according to the concept of size effect and the mechanismof shrinkage and creep; In view of the ACI209prediction model applied in the analysisof concrete creep and shrinkage less precision, the ACI209revised prediction modeltaking into account intensity influence coefficient was deduced on the basis of experimental data and research about HSC shrinkage and creep, and its validity wasverified against the variations of other prediction models and measures value, then,applied into the analysis of HSC box girder bridge creep and shrinkage, the predictionresults were less than that obtained from the ACI209prediction model.(3) In conjunction with a project of the experimental study on the shrinkage andcreep effects on the Xiang-Yu line Niu Jiao Ping railway large-span continuous rigidframe bridge, a series of experimental and analytical research on HSC creep andshrinkage have been performed in this dissertation, and some reliable experimental datawas obtained. Due to the large theoretical thickness of components among thesebox-girder sections, the finite element model with different creep and shrinkageprediction models has been established in Midas, dividing the sections into three partswhich are top, web and bottom slabs, a detailed analysis on the shrinkage and creepeffects in the bridges was subsequently conducted. The validity of the method is testedagainst strain data obtained from field measurements. The results revealed that to theanalysis of shrinkage and creep effects of HSC box girder bridges, the revisedprediction model and GL2000model come with better calculation accuracy. And theshrinkage and creep effects at early age of HSC bridge develop rapidly, whereas, thedevelopment later is rather slower; Finally，some potential variations of shrinkage andcreep effects on HSC box-girder bridge have been revealed with a comparative analysisof the change tendency of concrete strain in the thinner top, web and the thicker bottomslabs of the box cross sections, expecting to provide a reference for related research andinvestigation in the future.