Shrinkage And Creep Effect Of Long-Span Continuous Rigid Frame Bridge And Calculation Method Research

In recent years,the transportation infrastructure of our country has developed rapidly and the demand of bridge construction has become increasingly urgent.long-span continuous rigid frame bridges have shown greater advantages than other type of bridges in terms of spanning capacity,driving comfort and construction convenience.Thus,the number of this bridge continues to grow.However,in the course of long-term operation,some bridges have appeared the phenomenon of continuous cracking and deformation,which seriously hindered and restricted the sustainable development of such bridges.Generally,the emergence of such problems mainly due to shrinkage and creep,loss of prestress and the accuracy of the calculation method.Shrinkage and creep are the most influential and intractable problems,they are not yet been thoroughly studied.The study on the shrinkage and creep effects of concrete under the conditions of changing temperature and wetting in the natural environment and concrete creep recovery is particularly lacking.Therefore,no matter whether it is for the repair and reinforcement of already-established long-span continuous rigid frame bridges which continuous cracking and deformation,or for the design of such bridges in the future,it is necessary to continue to carry out deeper basic research work on concrete shrinkage and creep problems.As the core content of the National Natural Science Foundation of China “Deterioration process and decay mechanism of long span prestressed concrete box girder bridges”,this paper systematically studies the shrinkage and creep of concrete in the operation stage of long-span continuous rigid frame bridges.First,this paper summarizes the mechanism and influencing factors of shrinkage and creep of concrete.The shrinkage and creep models such as CEB-FIP series model,ACI209 model and B3 model,which are widely used at present,are selected for comparison and analysis.Then,reasonable suggestions for model selection are given.In order to study the effect of shrinkage and creep on the time-varying effect of long-span continuous rigid frame bridges during operation,a long-span continuous rigid frame bridge in Yunnan Province is selected to study its deflection and section stress based on three different shrinkage and creep models.The results of the study show that there is a close relationship between the deflection and the cross-sectional stress during the operation of large-span continuous rigid frame bridges.Also,the stress in the section of the top plate,near the middle of the web and part of the floor continues to decrease.After comparativing and analysising various existing related calculation methods,this paper proposes a concrete creep effect calculation method which can comprehensively consider many factors(temperature,humidity,reinforcement ratio,etc.)of natural environment,degressive stress and creep recovery.At the same time,the calculation method of total strain(including shrinkage,creep,elasticity and temperature strain)of the structure under natural conditions is put forward.The algorithm proposed in this paper has unique advantages such as clear physical meaning,comprehensive consideration and convenient program calculation.The results in this paper can promote the development of concrete shrinkage and creep calculation theory,and provide basic theoretical support for the analysis of continuous cracking and deformation problems in the operation process of long-span continuous rigid frame bridges.At the same time,it is of great significance for the design,reinforcement and accurate prediction of cracking and deflection of such bridges.