Research On Temperature Field And Temperature Effect Of Box Girderin P.C. Cable-stayed Bridge

Temperature action effect of concrete box-girder affects directly safety during construction and reliability during service. Statistical datum and researches have indicated that some cracks of concrete box-girder are caused by temperature action, which results from lack of in-depth research on concrete box-girder temperature field basing on systemic observing datum. Based on long-term observation data of the Yibin Changjiang River Bridge in Sichuan province, the temperature field and effects of temperature action in concrete box-girder are researched. The main research content and conclusion of this thesis are as follows:Continuous observation of temperature field in concrete box-girder of the Yibin Changjiang River Bridge lasted 4 months. The change regularity with time is analyzed detailedly for temperature field in each concrete box-girder components in the cases of natural environment, such as solar radiation and temperature drop. Research indicates that under the daily atmospheric temperature, the curve of concrete box-girder is sinusoid approximately, whose periods is 24 hours.The 3D problem of concrete box-girder temperature field is simplified to 2D problem, and the formulation of the time hysteretic properties of temperature field in concrete box-girder is proposed. It proves in theory that the periods of daily temperature agrees with the periods of concrete box-girder temperature.The factor influencing positive temperature-gradient-curve of concrete box-girder is discussed detailedly based on the thermal analysis of software ANSYS. Relative positive temperature-gradient applicable for China is discussed, it proves that positive temperature-gradient can be expressed as exponential curve. The expression of exponential curve is brought out to describe positive temperature-gradient of this bridge in this dissertation. Moreover, the relation of different factors to positive temperature-gradient is determined quantitatively. It is proved that solar radiation and change range of daily temperature are main impedance factors.It is used to calculate temperature effect with exponential function model by software Dr.Bridge. The result is compared with the result which is calculated by the designer. It shows that the stress of concrete box-girder and elevation of cantilever change little with integral temperature difference but biggish with the different temperature-gradient of box-girder and temperature difference between box-girder and suspended cables, and they influence differently.