Investigation On Effects Of Temperature Gradient Formed By Solar Radiation On Orthotropic Steel Bridge Decks

Solar radiation temperature gradient driven by solar radiation has a significant impact on bridge structures,which attracts more attention in engineering field.Vertical temperature gradient model is described in the Chinese General Specification for Design of Highway Bridges and Culverts(JTG D60-2015).Since the territory of China is great and the forms of bridge type are various,the distribution and affection of temperature effects caused by sunshine are different.Orthotropic steel bridge deck(OSBD)is widely used in bridge engineering due to their unique economic and structural superiority.However,steel has good capacity of thermal conductivity,the stress performance of Orthotropic steel bridge deck affected by the distribution of gradient temperature field may be significant.Considering the Sanchaji Bridge across the Xiangjiang River,temperature field and effects of temperature gradient action on orthotropic steel bridge deck are investigated.In this paper,the main work and conclusions are listed as follows:(1)The factors that affects temperature field of bridge are introduced.Then,heat transfer theory and the calculation of temperature stress are described.Finite element equations of temperature field are derived based on finite element theory.(2)24-hour temperature measurement of steel box girder was conducted under very hot and strong solar radiation condition in a summer day.The temperature distribution and variation characteristics of the top and bottom plate of box,as well as the upper and lower sloping wed of fairings under sunny condition are analyzed systematically.The characteristics of vertical temperature gradients of U-ribs,the upper and lower sloping wed of fairings and the diaphragm are obtained.Based on the measured data,the formula of linear function and exponential function are adopted to model the vertical temperature gradient of the steel box girder.The result indicates that the steel box girder shows obvious "box-room effect" under sunlight conditions,and temperature change rate of U-ribs is larger than that of diaphragm in the direction of temperature gradient.It is reasonable to fit vertical temperature gradient of box girder by piecewise functions.(3)Finite element model of OSBD is established,and its boundary conditions are based on the measured data.The distributions of temperature field at various times are obtained,and the results are compared with the field measurement of the cutout.It shows the rationality of the finite element method and the assumptions of temperature field calculation.(4)According to the results of temperature field analysis,the temperature stress of OSBD under solar temperature gradient field is obtained by finite element method.The results show that there is a large temperature stress at the structural details of the OSBD.and the maximum temperature stress is located at the lower end of the welds between the U-ribs and diaphragm.The results show that the influence of gradient temperature field on the bridge structure cannot be ignored and should be paid attention to in the research,bridge design and construction.