Study On Shrinkage & Creep And Temperature Field Of Long-span High Speed Railway Reinforced Concrete Rigid Skeleton Arched Bridge

With the rapid development of China's high-speed railway,ordinary prestressed concrete bridge structures have a large proportion along the railway line with their desirable features of economical and greater rigidity.For the railway crossing deep valleys,long-span stiff skeleton concrete arched bridge has a superior overall mechanical performance making it a highly competitive in the selection of long-span bridge structures.However,the long-term deformation behavior of bridge structures as a result of shrinkage and creep of concrete material is not widely understood and is thus of the key research interest in China and other countries.The current experimental research on concrete shrinkage and creep is mainly carried out under standard environmental conditions such as constant temperature and humidity.The prediction models may have a good prediction result for the concrete shrinkage and creep under standard environmental conditions.However,there is a large deviation in the prediction of concrete shrinkage and creep between natural and standard environmental conditions.Therefore,it is necessary to carry out research on concrete shrinkage and creep prediction model under natural environmental conditions,which provides theoretical basis for engineering practice.For the concrete bridge in the natural environment,the solar irradiation will cause the non-uniform temperature distribution on the concrete box structure.For the ordinary linear concrete box structure,the cross-sectional inclination angle is fixed in the axial direction and the two-dimensional temperature field analysis can meet the basic requirements.For the long-span arched box structures,the cross-section inclination angle is constantly changing along the arch axis.The temperature variation laws of the box roof along the arch axis are different under the solar radiation effect,and the analysis of two-dimensional temperature field cannot meet the basic requirements.It is necessary to carry out research on the three-dimensional temperature gradient distribution laws of arched box structure,and provide technical support for the construction of similar bridge structures.This dissertation combines the research and development plan of the Ministry of Railways,and the main research contents are as follows:(1)The experiments of concrete shrinkage and creep of C60 and C80 high-strength concrete in the main arched structure were carried out,so to fully understand the long-term deformation behavior of concrete shrinkage and creep under natural environment.(2)The existing concrete shrinkage models were summarized and the main factors affect the long-term shrinkage behavior of concrete were analyzed.Based on the shrinkage models under standard conditions,the influence laws of temperature and humidity of concrete shrinkage under natural environmental conditions were studied.The ambient temperature correction coefficient and the wind speed affects the concrete humidity correction coefficient were considered.The concrete shrinkage model under natural environmental conditions was established and the calculated results were compared with the experimental results to verify the accuracy of the model.(3)The existing mainstream concrete creep prediction models and the main factors affect the long-term creep behavior of concrete were summarized,so to discover the distribution laws of internal temperature and humidity of concrete under natural environment;the model was modified by introducing the influence coefficient of concrete humidity and ambient temperature,at the same time,the instantaneous acceleration of concrete creep was considered to describe the long-term creep behavior of concrete under natural environment.The calculated results were compared with the experimental results to verify the prediction accuracy of the model.(4)Through the comparative analysis of the experimental results of shrinkage and creep of ordinary concrete and concrete filled steel tube and the research on the prediction models of domestic and foreign scholars,the main influencing factors affect the shrinkage and creep of concrete-filled steel tube were studied.The prediction method of CFRP creep model considering expansion agent,steel rate,recycled aggregate replacement rate and ambient temperature was proposed,and provides a reference for the perfection of the CFRP model.(5)Based on the theory of existing concrete temperature field,the calculation method of the comprehensive atmospheric temperature of concrete box structure under the effect of sunlight was proposed.The value of long-wave radiation heat transfer coefficient was discussed,the different combinations of ambient temperature and the temperature of box structure were studied and the reasonable range of long-wave radiation heat transfer coefficient was proposed and the calculation accuracy was improved.(6)The temperature field experiment of the arched box structure was carried out and the three-dimensional temperature field distribution laws of the non-flangeslab arched box structure with changing inclined angle along the arch axis were discovered.(7)The two-dimensional temperature field models of concrete box structure of domestic and overseas were summarized.Combined with the calculated results of the finite element model,the temperature gradient eigenvalues of different cross sections along the axial direction were obtained and the three-dimensional temperature gradient models of the non-flangeslab arched box structure were established.(8)The finite element model of the 445 m arched box structure was established.Based on the research results in this dissertation,the concrete shrinkage and creep and ambient temperature effect on the long-span high-speed railway stiff skeleton concrete arched bridge were studied.In the end,the comparison between the experimental results and the theoretical results was discussed,and the development laws of deformation and stress of the arched box structure under the influences of concrete shrinkage and creep and the ambient temperature were obtained.