Study Of Temperature Effects On Concrete Box Girder Bridges

Environment temperature is one of the main factors that cause cracking of concrete box girder bridges. The temperature effects of box girder bridges is closely related to the structure size, the constraint condition and the acting time. The main work in this paper is as follows:1. Based on temperature data measured in a prestressed concrete box girder bridges, the distribution of temperature field of concrete box girder bridges is studied. General factors affecting temperature field are summarized, including position factors, environment factors, material factors and section size factors, and their's influence law are analyzed. Under action of sunshine, change of temperature field in the roof is largest, change in the web is smaller, and change in the bottom is smallest. The vertical temperature difference of box girder cross section is relative large and the transverse temperature difference exists. Amang the factors influencing temperature field, sunlight radiation, speed of wind and temperature difference in a day have a great influence on temperature field and temperature difference of cross section.2. According to the measured temperature gradient model, distribution and mechanism of temperature effects in a box girder bridge are studied. Sensitivity analysis are carried out on parameters affecting temperature effects distribution, including thickness of the roof, web and floor, the height and width of the box girder and the laws that parameters affecting temperature effects is analyzed. The results show that change of section size of a box girder leads to the change of section stiffness so that stress distribution in the roof, bottom and web is also affected. Thickness of roof, web and the height of a box girder have a relatively larger impact on temperature effects distribution.3. The distribution of temperature effects in a continuous girder bridge and a continuous rigid frame bridge are studied under the same temperature gradient mode and effects mechanism the boundary condition and structural type have on temperature effects are analyzed. It is discovered that boundary conditions and structure type are the primary cause leading to difference of temperature effects.4. Unified temperature difference in the roof, the distribution of temperature effects produced by different temperature gradient mode specified in several bridge codes are compared and studied, and the difference mechanism are analyzed and pointed out In different temperature gradient mode, the value of temperature difference along height of box girder, difference of action form and depth difference of action cause difference of temperature effects.5. The law of the stress distribution is fitted, the coefficients are expressed as a function of the parameters and the law is verified. There is a certain difference in the measured value, the calculation value and the fitting formula and the distribution law is quite consistent. It is feasible to use the formula to describe the distribution law of stress.6. The existing damage models are analyzed, a new form of damage expression is proposed and parameters in the expression are fitted, which lays a foundation for further research on the long-term effects of temperature.7. The load spectrum of temperature action is established and the long-term temperature effects of a box girder bridge is studied, which is compared with the long-term effects of a box girder bridge under vehicle fatigue load. The influence causing by repeated action of temperature and vehicle load are analyzed. The long-term effects of temperature on the box girder bridge is far greater than the impact of vehicle load and the stiffness of the cross section is also gradually degraded.