Study On Shrinkage And Creep And The Long-term Deformation Of Prestressed Concrete Box Beam

In recent years,with the rapid development of transportation,prestressed concrete box girder bridge with its excellent overall mechanical performance,economical and simple construction and other features have been widely used.But mostly during the operation appeared shrinkage and creep of concrete and long-term performance issues that hinder further promote bridge-type.Although concrete creep and shrinkage has been a lot of research,but due to the complexity of the issue,has not been very good forecasting model.In addition,the long-term performance of the study is relatively small,the results of the study have yet to be further improved.this paper combined key projects in Hunan Higher Scientific Research "Modeling and analysis of the role of prestressed concrete box beam effect shrinkage and creep" research.Through two prestressed concrete simple box beam is applied to long-term load,in-depth study of the long-term mechanical performance.The main work is as follows:(1)The prediction model of concrete shrinkage and creep at home and abroad is introduced in detail,including the CEB-FIP series model,B-P model,ACI209 series model and GL2000 model.The mechanism of shrinkage and creep and its main influencing factors are discussed in this paper.The calculation theory of the shrinkage and creep effect of the structure and the basic premises,the scope of application and the advantages and disadvantages of each theory are discussed;(2)For the uncracked beam the mid-span deflection after one year is 1.9 times of its instantaneous deflection;For the cracked beam the mid-span deflection after one year is smaller than that of uncracked beam,and the gap increases with time.The cracks leads to the releasing of concrete stress and results in significant the decrease of the creep influence;(3)The long-term deformation of the test model is predicted by the current standard method in our country,and the theoretical value is higher than the experimental value,which indicates that the influence of the crack on the long term deflection should be considered in the formula;(4)based on prestressed concrete simply supported box girders long mechanical tests,a detailed study of the long-term impact of crack deflection Development.While takingadvantage of the variational principle and the principle of superposition to analyze,consider the impact of the establishment of a multi-factor formula of long-term deflection.Combined with the measured creep factor for long-term deflection test beams were calculated and analyzed by performing a comparative analysis to verify the accuracy of the calculation formula and long-term deflection measured value.