Analysis Of Temperature Field And Temperature Effect For Concrete Box Girder In Severe Cold Area

The temperature field of concrete box girder is influenced by many factors,and the distribution in different regions has its own advantages.According to the general temperature gradient model and the value of the current standard,the temperature stress calculation and crack prediction of the structure will bring the inevitable error.At the same time,the unique climate characteristics of Xinjiang Altay Habahe County create a distinctive temperature development and distribution of box girder.To ensure the smooth construction and safe operation of bridges,establishing a local temperature field model is necessary.A box girder segment was constructed in Xinjiang Habahe,meanwhile,the hydration temperature field and the sunshine thermal field of the box girder model were measured by479 thermocouples in 1/2 cross section.Delaunay triangulation method was employed to establish a thermometry matrix,and then the temperature variation characteristics and the solar effects were analyzed.The following conclusions are obtained:(1)The hydration temperature displays a symmetrical distribution across the vertical center axis of box girder segment.The maximum of hydration temperature is located in the box-girder web with a value of 64.8?.The ratio of maximum hydration heat of top,bottom flanges and webs of box girder is 1:1.1:1.4.The solar temperature field is asymmetrical in warming period,which lasts 11 hour in September,only 8 hour in December,and the ratio of bog-girder average temperature rise amplitude between September and December is about7:3.(2)The maximum hydration heat occurs within 11 hours after concrete casting in bottom flange,while it is 12 hours in the web and 13 hours in the top flange of box girder.Under the effect of radiation,the temperature difference between the eastern and western side of top flange is small,while the phase difference of webs and bottom flange are exists,the eastern side reaches the extremum 1~3 hours in advance,and the extremum achieved in September is about 2 hours earlier in December.(3)The temperature variation in thickness direction of plate follows an expression of Gaussian function,while the temperature variations in width direction of top and bottom flanges follow a binomial expression of Gaussian function.In addition,the temperatures mainly keep in constant in height direction of box girder's web.(4)The box girder outer surface temperature variety is obvious,so the solar temperature gradient in thickness direction of plate experiences negative temperature difference-positive temperature difference-negative temperature difference process.The maximum positive temperature difference occurs in eastern web,and the difference in December is about 90%in September.While the negative attains in bottom,the ratio between September and December is 1:0.75.(5)The temperature variation in width direction of top and bottom flanges undergoes the bimodal symmetry distribution pattern,the east-high west-low bimodal asymmetric distribution pattern,the west-high east-low bimodal asymmetric distribution pattern,and the bimodal symmetrical distribution pattern.The eastern peak temperature is higher than west,the bottom temperature gradient is 2.5?larger than top flange,and both of them arises the most unfavorable temperature gradient at 14:00 pm.(7)Temperature stress is caused by nonlinear temperature gradient.According to the stress theory formula,the gradient can divide into the vertical temperature distribution T(y),the average temperature T_m and the equivalent linear temperature gradient?T,these causes the temperature stress of clamped box girder,expansion stress and rotational stress of the box girder without restraint.The actual temperature distribution T(y)determines the stress distribution curve style,while T_m and?T perform translational and rotational operations on the force distribution curve.