Study On Shrinkage And Creep Effcet Of Widened Concrete Girder Bridge

Based on the national natural science fund "Fundamental Theories for theWidening and Reconstruction of Existing Concrete Bridges (51278182)", etc, theresearch is focused on the influence of shrinkage and creep to the concrete griderbridge widening and splicing. This thesis involves mainly the following investigationsand corresponding results:(1) The shrinkage and creep model in domestic and international are quitedifferent. Using different shrinkage and creep model may lead to different evaluationof structural safety, especially in the project to widen and splice a bridge. Theparameters of shrinkage and creep model in <Code for Design of Highway ReinforcedConcrete and Prestressed Concrete Bridges and Culverts>(JTG D62-2004) areanalyzed. Results show that: the theoretical thickness of structure component has agreat influence on the shrinkage strain of concrete, so that the changes of theoreticalthickness caused by the construction process should be considered;(2) Based on the shrinkage creep model of JTG D62-2004, considering thedifferent solution schemes and bearing arrangement, the axial and transverse effectsof a widened22-span concrete T-girder bridge caused by shrinkage and creep areanalyzed. Results show that: the shrinkage and creep difference between the new andexisting bridges leads to significant axial and transverse effects of the existing one;the structural transverse effect can be significantly reduced after cutting the existingbridge to some100-150m short parts to do the widening and splicing. Meanwhile, thestructure axial force is relatively simple and uniform. In addition, by using theminimum strain energy standards and objective function optimization method, thebearings arrangement of a100m project is discussed. More reasonable plan of itsbearing arrangement is achieved, which provides a new idea for analyzing theoptimized bearings layout in the bridge splicing;(3) Based on the JTG D62-2004shrinkage creep model, with consideration of theinteraction of superstructure and substructure, the transverse effects of widenedconcrete box-girder bridge caused by concrete shrinkage and creep are studied in thepresent paper. The results suggest that: the interaction of bridge superstructure andsubstructure significantly effects the performance of widened bridges; the differenceof concrete shrinkage and creep between the existing and the new structure lays a much greater influence on the transverse and axial effects than the vertical effect inthe widened bridge girders; the transverse effects would lead to decrement of thecompression-resistant capacity of the piers, which results from the additionaltransverse horizontal force at the support on the top of the piers; also, it changes theinternal force of the girders in those existing bridges from uni-axial bending tobi-axial bending with axial compression, which should be seriously considered.(4) A bidrectional loading nonlinear numerical analysis program is compiled toanalysis the ultimate vertical bending bearing capacity of normal section on thetypical bridges such as box girder, T-girder, hollow slab after broadening underbidrectional force.The program calculation results are compared with the ultimatebearing capacity empirical formula calculation results of double bias compresscomponent and the ultimate vertical bending bearing capacity of normal section of oldbridges before broadening. Results show that the cross section flexural bearingcapacity of the broadened bridge increases or decreases comparing with the old bridgeand the program can effectively predicts the normal section vertical bending bearingcapacity of the existing bridges after splicing.