The Research Of Temperature Field And Hydration Heat Effect On The Long-span Prestressed Concrete Box Birder Bridge

It is easy for prestressed concrete box beam in the construction process to crack, the temperature of the early shrinkage cracks are more common which has been widespread concerned by the engineering sector.research on the temperature effect of long-span prestressed concrete box girder bridge is still not perfect. The design codes on concrete box girder bridge temperature gradient model vary from country to country. With a vast territory, China has a great difference in regional climate. However, we still apply one stereotyped temperature gradient model which seems unreasonable at all. In this paper, we take the Weishui main bridge of the Chang-Xiang expressway (double track) Xiangjiang river bridge as the project background. By field measurement of the internal temperature distribution of box girder, combined with adopting finite element program ANSYS and Midas/Civil, we have analyzed the temperature field, temperature effect and hydration thermal-effect of prestressed concrete box girders and explored the formation causes of the early cracks of the long-span prestressed concrete box girder bridgeThe main research contents and results of this paper are as follows:(1)By using finite element program Midas/Civil to establish the finite element model of the entire main bridge of Weishui, and analyzing by comparing concrete box girder temperature gradient models in the bridge design specifications of different countries, we conclude that the temperature stress for temperature difference of Chinese railway bridges and New Zealand bridges are rather big. Compared with 85 bridge rules, the 04 bridge rules have achieved remarkable improvement on the provisions for temperature stress. And we also get the result that the temperature stress caused by sunlight temperature difference in the design codes of different counties is large in the midspan cross-section of the pillar top and small in the bridge pier top cross-section.(2)Observed the temperature field of spring and summer on the bridge site , found that the influence to the roof floor is bigger than the base floor when the temperature is exceed 15 degree;Due to the larger difference between day and night of temperature, the main conclusions of the negative temperature-controlled. Making a Comprehensive analysis of relevant literature and field data, experimenting and probing into the temperature parameters (convection coefficient, thermal radiation coefficient, the thermal conductivity, specific heat capacity, guide temperature coefficient, etc. ) and mechanical parameters (expansion coefficient, elastic modulus and poisson's ratio, etc.) which affect the concrete structure temperature field distribution, and providing technical guidance for simulation analysis based on the heat transfer theory and the meteorological data obtained.(3)By using finite element analysis program ANSYS to establish box girders of two-dimensional entity model, conducting transient analysis of the temperature field, and comparing the calculated results with the actual date by field measurement, we get the result of vertical concrete girders of nonlinear temperature gradient fitting curve and the suitable concrete girders temperature gradient model for the site of bridge.(4)Conducting hydration heat analysis on Weishui main bridge, tapping into the formation causes of the early cracks of base plate and web plate and proposing corresponding construction control measures so as to provide references for future construction by using finite element program Midas/Civil to establish 1/4 model of the 0/1# bridge beam section of Weishui main bridge, combined with field measurement.