Research Of Temperature Field And Temperature Stress Of Railway Prestressed Concrete Box Girder Caused By The Solar Radiation

It is an important research field in bridge structure that the bridge structure thermal stress and deformation will be affected by the meteorological factors, such as seasons, temperature variation and solar radiation. Many studies show that the concrete thermal stress under solar radiation can reach or exceed that under live load. Besides, the thermal stress and deformation of concrete box girder caused by different temperature will directly affect the safety, durability and serviceability of bridge structure. However, the mode of temperature gradient of concrete box girder has obvious regional characters due to different climatic conditions. Domestic and foreign regulations on the temperature load can not be applied to all of the bridge structure.Further more, the existing research results in the actual project application also have certain limitation.Therefore, further studies are necessary to the temperature field and thermal stress of concrete box girder.According to the solar physics, astronomy and heat transfer theory,the thermal boundary conditions in concrete birdges subjected to solar radiation are defined,the total heat flux of each parts of the box girder are systematically analyzed. The calculation formula of the solar incidence angle was proved for the first time by using the cosine theorem.Based on the geometry of space, The general formula for calculating webs shadow length are derived. The calculation model of simulation analysis of box girder temperature field and temperature stress is established with considering the shielding effect of flange on the web.In this thesis,the general variation of the temperature field, thermal stress and temperature gradient were investigated by means of site measure and the ANSYS finite element analysis, with the Yuanjiang Bridge which is located in Shanghai-Kunming passenger dedicated railway line as the research target. Experimental research and finite element analysis in the process of research complement each other, on the one hand, calculated values reflect the rationality of measured values, on the other hand, the measured values confirmed the reliability of the calculated value. Based on the observation data of four days in the day time, change law of the temperature of each part of the box girder are analyzed, such as the ambient temperature, the roof, web and bottom etc. The relationship between the internal and external surface of box girder temperature difference and temperature gradient are studied. Besides,the time-varying temperature stress of box girder flange plate, the top plate and the bottom plate are analyzed. Then, compared the measured vertical temperature gradient of each moment of box girder, and what time the most unfavorable temperature distribution appear is determined. Comparing the measured temperature gradient and temperature gradient of domestic and foreign bridge specification, found that each specification has some limitations. In addition, focuses on the research of the change law of box girder vertical temperature difference with time, and summarize the regularity of temperature gradient expression can reflect the Yuanjiang bridge box girder cross-section changes in sunshine duration range. Finally, the reliability of the finite element method is confirmed. Through the finite element analysis, whether the thermal stresses of concrete box girder under the extreme case will exceed the limit value problem is discussed.