Analysis On Creep Effect On Continuous Rigid Frame Bridge Using Prestressed Concrete

Prestressed concrete structures and large-span structures, in which strength ofconcrete rose constantly, are booming in recent years. Creep in the structures above ispaid increasing attention by people. Shrinkage and creep are intrinsic properties ofmany materials, especially concrete. Creep of concrete lasts from its curing period to theend of its service period. The higher strength and larger span, the more influence will bebrought by creep, especially in large-span bridges and pre-stressed concrete bridges. Forinstance, creep leads to loss of pre-stress in pre-stressed structures and reduces camberin large-span structures. Time-dependent deformation of structures consists of creep,elastic deformation, shrinkage and temperature deformation. And creep deformation canreach a value which is2~4times of elastic deformation’s value, thus, it is necessary toconsider creep’s impacts on structures in design. Nowadays all the existed predictionmodels around the world are only suitable for ordinary concrete with a strength lowerthan C40or lightweight aggregate concrete with a strength under LC30, however, thereexists no prediction model for prestressed concrete structures and large-span structure.In particularly, high-strength concrete used in large-span bridge is in urgent need forfitted prediction model of shrinkage of creep.Based on the collection of a large amount of data, experiments and examples, mainworks in this paper are as follows:①Comparing influence factors, mathematical expressions and precision level ofdifferent creep prediction models, like China Academy of Building ResearchModel(1986), CEB-FIP(1978),ACI209(1982),BP series, GL2000and Japanese"Concrete Codes". Based on B3Variation Coefficient Method, quantitative analysis wasconducted on different prediction models, whose results showed that the wholeperformance of GL2000was the best, followed by B3Model and Japanese ConcreteCodes Model.②Proposed an approach named "Step Method" to divide time section and iterative bysome basic assumptions. Experimented shrinkage and creep of high-strength concrete,and found large deviation between test data and existed models. Thus, by modifying themodel in Japanese Concrete Codes, a modified model was proposed, fitting test data andprogramming to compute creep coefficient.③Analyzing on data of strain and deflection of Niujiaoping Bridge after long-term observing. Based on Abaqus Scriping Interface, new user’s material properties that fittedACI209(1982) and Modified Model were created by Python. By comparing results ofcalculation and test data, a rule of creep’s progress was obtained that fast progress increep strain and deflection was found in early loading ages, for example,70%~80%infirst3years after which developing speed slowed down.