Accurately Analysis Of Shrinkage And Creep Effect For Presressed Concrete Box Gider Bridges

Shrinkage and creep are the inherent time-dependent characteristics of concretematerial，it will make a significant effect on concrete the force and deformation of concretestructures. Especially the prestressing system in the prestressed concrete box girder bridgesare very powerful, so concrete will have higher stress,shrinkage and creep effects in it willbecome more apparent. Shrinkage and creep makes the stress redistribution on the section ofthe statically indeterminate structures,and makes the internal force redistribution of staticallyindeterminate structures,and makes the prestress be lossed, and makes the structures have alarge deformation. At present main using the beam theory to analysis the bridegs’ shrinkageand creeep effect, and lacking of the solid theory about it. Shrinkage and creep effect ofconcrete and relaxation of prestressing tendons on the bridge is being consideredseparately,and not taking into account the mutual influence of them. This article based on theabove questions, and do several works as follows:At first, Making a complete summary about the shrinkage and creep mechanism andfactors. Evaluating the principle of the theory of computation, and the degree of precision, andthe Scope of the using. Comparing the model formula, the factors and degree of precision ofthe.ACI-209model, the CEB-FIP model, model B3, and GL2000model.It takes way to selectthe prediction model.Then building60m precast box girder’s finite element model by MIDAS/CIVILprocedures which is based on beam theory and by ANSYS program whicm is based on solidelements.The model consider the relaxation of prestressing tendons on concrete shrinkage andcreep effect，and make a finite element theoretical analysis, and compares with experimentalvalues And result shows that the effect of shrinkage and creep makes box girder bridge largedefomation,and Significant stress redistribution.Finally, Using ANSYS software, based on the solid elements, and considered therelaxation of prestressing tendons on concrete shrinkage and creep,making a finite elementmodel about a continuous rigid frame bridges which’s main span is160m, The results showthat with the influence of shrinkage and creep，operation of the bridge’s mid-span deflection is three times as the completion of bridge; and the main compressive stress of the beam’s web isreduced；and the beam’s axial compressive force decreases; and the bending moment in thepier top section increases; the bending moment in the section main span’s mid-span increases.Shrinkage and creep is the main factor to cause long-term prestressing loss.