Observation Of Temperature Field Of East-west Direction PC Box Girder In The Central Region (Xiang Zhong) Of Hunan

The conductivity of concrete is so small that structure internal temperaturechange exists obviously hysteresis phenomenon when concrete bridge under the ac-tion of solar radiation and temperature changes which belong to the external envi-ronment factors. That causes the heat which each layer of concrete obtains or spreadsexisting big difference and forms the Nonlinear distributing temperature status. Theoverall warming or cooling status has already been considered in bridge design andthe method to calculate is simple. But there is no consensus on which form the tem-perature field spatial distribution curve is which also can be said the load of sunshinetemperature gradient in concrete bridge structure. Simultaneously, because there islarge difference on the regional climates in our country, the calculation cannot takethe uniform temperature load for the bridge structure which is under the different lo-cal environment. So, studying the temperature field of concrete bridge structure in theoutdoor atmosphere under different climate conditions in different regions and estab-lishing the temperature load model of the different regions in china are very neces-sary.This paper mainly studies the variation law in time and space of the temperaturefield in the east-west direction PC box girder which is in the central region (XiangZhong) of Hunan under the sunshine temperature load. With the background of theapproach span (prestressed concrete box girder bridge) to Xiang River extra-largebridge in the Chang Xiang expressway, the temperature field during the summer andwinter seasons are observed to study the temperature field of the surface both insideand outside of the prestressed concrete box girder changing law in time and the spatialdistribution in structure. Fluke Ti25infrared thermal imaging camera is used to ob-serve the temperature field. Base on four-cross section, characteristic temperature ofkey points variation law of diurnal and seasonal are analyzed which are inside andoutside of the sections on the surface. The spatial distribution curve of temperaturefield is analyzed in the structure of this bridge, Simultaneous, the sunshine tempera-ture gradient is compared with several counties load code and the corresponding yearoverall temperature changes are geted.Results display that under the sunshine temperature load, the surface heatingand cooling temperature of PC beam and related points temperature difference fluc-tuate with outdoor air temperature. The year overall temperature difference is similar with that General Code for Design of Highway Bridges and Culverts proposes. Thetemperature difference is small in the transverse section of the eastwest trend bridge,so it can be ignored, and verify that the temperature uniformly distributes in the in thelongitudinal direction. The temperature field is nonlinear distribution on the box beamsection along vertical. The heating load curve drops quickly from the roof downwardapproximately40cm, and then tends to be steady. The drop slop of the curve of tem-perature gradient load is smaller than that proposed by Chinese railway concretebridges design code, but that is similar than that proposed by Chinese highway con-crete bridge design code, and there is negative temperature difference in the bottom ofthe bridge cross-section. The cooling load curve rises fast from the roof downwardapproximately60cm, and then tends to be steady. The rise slope of the curve of tem-perature gradient load is smaller than that proposed by Chinese railway concretebridges design code and Chinese highway concrete bridge degign code and there ispositive temperature difference in the bottom of the bridge cross-section.