Observation And Analysis Of Prestressed Concrete Continuous Box-Girder Temperature Action

Temperature action effect affects directly safety of concrete box-girder. 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. Therefore, to research and perfect the theory study and calculating method of temperature field in concrete box-girder basing on long-term observation data is the purpose of this dissertation. The main research content and conclusion of this dissertation are as follows:Continuous observation method is used to observe temperature field in concrete box-girder of a long-span high-way bridge. 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, temperature drop, and stable natural environment in spring and autumn. Research indicates that under the daily atmospheric temperature, the curve of concrete box-girder is sinusoid approximately, whose periods is 24 hours.Hypothesis testing and parameter analysis are used for the statistic analysis of temperature field in concrete box-girder. A method for calculating the temperature action representative value is developed according to long-term observation data. Representative value of temperature action is calculated by this method. Hypothesis testing and parameter analysis indicate that daily difference in temperature of concrete box-girder in summer without asphalt concrete cover follows Weibull distribution with parameter 9.1327 and 2.61837, it in winter follows Weibull distribution with parameter 4.4392 and 2.0749.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 range ratio and phasic difference of concrete box-girder temperature to daily temperature is quantitated.The factor influencing positive temperature-gradient-curve of concrete box-girder is discussed detailedly, relative positive temperature-gradient applicable for China is discussed, it proves that positive temperature-gradient can be expressed as exponential and bilinear curve. Moreover, the relation of different factors to positive temperature-gradient is determined quantitatively. It is proved that height of bottom corner of top plate, solar radiation and change range of daily temperature are main impedance factors. Datum fitting indicates that the relationship of height of bottom corner of top plate and parameter a of expression of positive temperature-gradient is linear.The most unfavorable position of three-span prestressed concrete continuous box girder is located at the bottom of top plate of mid-section in the middle span.