The Most Unfavorable Solar Temperature Field And Termal Stress Of Long-span Concrete Box Girder

Long term exposure to the natural environment,the bridge will certainly be influenced by solar radiation,temperature changes and other factors in its full life cycle.And the temperature effect is one of the main factors that cause the cracks of concrete box girder bridges.Now,there is no uniform regulation on the temperature distribution mode of concrete box girder bridges.At the same time,due to the different climatic conditions,the temperature distribution model has obvious regional characteristics.Under marine environment,the distribution of temperature field for concrete box girder bridge is different from other regions.The cracks caused by temperature influence the safety,serviceability and durability of concrete box girder greater.Therefore,to research the most unfavorable temperature field and temperature stress of concrete box girder bridge under marine environment,and to determine the temperature difference distribution in accordance with actual situation is of great significance to the follow-up similar bridge design.Firstly,the positive temperature field of Nachao River 2#bridge which is located in Cao Fei Dian industry-district is obsevered for ten days in summer during construction stage,also the negative temperature field is obsevered for three days in winter.Secondly,the distribution of temperature field and temperature stress for the roof plate,bottom plate and web plate of concrete box girder is analyzed.And the experimental datas are fitted to get the most unfavorable vertical and horizontal temperature gradient of the sea-crossing box girder in construction stage.Thirdly,the boundary conditions for the analysis of solar temperature field of box girder are established,according to the theory of solar physics,meteorology and heat transfer.Lastly,the finite element model is established in order to simulate the most unfavorable temperature field and temperature stress of concrete box girder,considering the shielding effect of long flange on the web.Nachao River 2#bridge in Caofeidian industry-district is given as an engineering example.The finite element analysis software ANSYS is used to calculate the transient temperature field of box girder in order to obtain the transient temperature cloud picture of test sections at different time.And the temperature time travel curve and the most unfavorable temperature gradient are compared with the measured curves,in order to verity that it's of high precision to use ANSYS for simulation of transient temperature field,based on the reasonable selection of environmental and thermal parameters.According to the principle of heat transfer finite element method,plane model is established by using ANSYS for heat-stress coupling analysis.The node temperature of transient thermal analysis is applied to the stress analysis as the load.The temperature effect of concrete box girder bridge,especialy the distribution of the lateral and longitudinal temperature stress in key sections is discussed.