Analysis Of Temperature Effect On Long-span Contin-Uous Frame Girder Bridge Over Construction Stages

Survey data of the domestic and abroad show that Early cracks for concrete is a general problem in construction practice of long span continuous box girder bridge. Among them, the effect of temperature is an important factor which affects the early cracks. The paper has took a long-span continuous rigid frame box girder bridge as the engineering background, analysis and study on the temperature gradient and heat of hydration of girder in construction stage. Put forward the corresponding temperature control measures, and provide a theoretical basis for the prevention and control of large span box girder bridge early crack problem.The paper use the3D temperature solid element in ANSYS10.0to calculate the box girder temperature gradient, the factors such as the solar radiation, air temperature, concrete surface absorption and heat radiating element are considered. The results were compared with the measured data, and the temperature gradient calculation model in the process of construction with no deck pavement are fitted to analysis the section stress during construction and the connection of the two halves of the bridge. And the paper use the software called Midas civil2012to calculate the distribution and changes of time-travel of hydration heat during box beam construction process rely on the actual project parameters.The results were compared with the measured data to test the correctness of the calculation results.The calculation results of temperature gradient and the hydration heat show, there are some differences between temperature field with calculation model of the standard of highway bridge over construction stage on long span continuous box girder bridge. The vertical and transverse temperature gradient suitable for exponential distribution. Because of the different shading effect of cantilever plate, the girder should be adopted in different temperature calculation mode at intermediate span and Side span. Box beam generated relatively large longitudinal and transverse tensile stress by the temperature gradient effect in the process of cantilever construction. Especially after the bridge closure. Longitudinal tensile stress is particularly significant in intermediate span by the common effect of temperature self stress and secondary stress. The heat of hydration effect makes the box girder appear larger tensile stress in the stage of box girder transfer position and the section angle of chamfer during the box beam cantilever casting process. Extremely easy to crack during construction. Reasonable casting time, the low heat of hydration of cement, the right amount of retarder, reasonable maintenance and construction scheme of the temperature control measures can be used, in order to reduce the effect of temperature in the process of construction of box girder as far as possible.The paper has beneficially explored the prevention of early temperature cracks in the large span prestress concrete box girder bridge, and can provide reference for design and construction of bridge.