Research On The Mechanism Of Concrete Shrinkage And Creep To The Construction Crack Of Frame Bridge

In the current high-speed development of traffic,with the increase of train speed and vehicle density,traffic jam has become a constraint factor of urban development.In order to solve this problem,the emergence of Underpass railway is inevitable.With the increase of the line density,the long-span box culvert is used more and more in the project;this kind of long-span box culvert is easy to crack in the construction process,which has a profound impact on the stability,safety and durability of the structure.In serious cases,it is difficult for the frame structure to bear the load imposed on the top of the box culvert after jacking.Controlling the generation of cracks in the construction stage has become a hot spot of current research.At present,it is considered that the main cause of cracks in the construction stage is caused by temperature stress,and the influence of shrinkage and creep factors has not been fully considered.Therefore,in order to control the generation of cracks in the early stage of frame bridge,starting from the mechanism of shrinkage and creep,this paper analyzes the relationship between shrinkage and creep and temperature and humidity The strain change considering shrinkage and creep is analyzed by numerical model.Through on-site experimental research,to explore the influence of temperature and humidity on the development of cracks,on-site humidity monitoring is difficult to achieve.In this paper,temperature difference and strain comparative analysis are used,and the development process of cracks is summarized;at the same time,the effect of shrinkage and creep on the stress change of different construction methods is considered,so as to provide crack control technology and relevant basis for such projects.Based on the concrete crack control project of Ningbo underpass railway box culvert,this paper analyzes the relevant changes caused by the temperature field and stress field through the contrast test of actual projects,explores the influence of different environmental temperature and humidity on the stress changes,analyzes the influence of different construction methods,discusses the location and width of cracks,and conducts field test By comparison,the following conclusions are drawn:(1)This paper analyzes the mechanism of concrete shrinkage and creep,and points out that the MC90 model have a better reflection in the change of concrete internal shrinkage and creep in the construction stage.At the same time,according to the shrinkage value of 30 days,the shrinkage equivalent temperature difference is 11.3 ?,and the shrinkage value of 90 days of mc90 model is 185 ? ?.The final creep coefficient is 1.1.(2)Based on the finite element analysis,the stress change of box culvert considering the shrinkage and creep is analyzed when the ambient temperature is 15?,20? and the ambient humidity is 70%,80% and 90%.It is found that the stress increase caused by the decrease of90% to 70% humidity is equivalent to the temperature rise of about 5?.The temperature andstress changes of the box culvert under the temperature of 10? and 25? were compared and analyzed,and the influence of the formwork replacement on the stress was explored.(3)According to the field comparative test of finite element simulation,the temperature and stress changes of box culvert under different temperature,different formwork and different ambient temperature are compared and analyzed.It is found that the stress peak value of the upper part of the portal section reaches the maximum.