Regional Difference In Temperature Effect Of Concrete Single-Box Multi-Cell-Box Girder

Prestressed concrete bridges are exposed to the natural environment and are subject to complex time-varying temperature effects due to bridge orientation,geographic location,temperature dips,convection,solar radiation,and structural shading.China has a large geographical area and a complex and diverse climate,and there are differences in the temperature effects(section temperature difference and effective temperature)of concrete box girders in different geographical areas.The current General Specification for Design of Highway Bridges and Culverts(JTG D60-2015)divides the effective temperature of concrete girder bridges into three regions,but the section temperature difference of concrete girder bridges does not take into account the geographical differences.In order to further explore the regional variability of the temperature action of concrete box girder,this paper investigates the temperature field test model of single-box multi-chamber box girder cast in Shannan,Tibet(highland alpine climate),Tongchuan,Shaanxi(temperate continental monsoon climate)and Laibin,Guangxi(temperate continental monsoon climate),finite element numerical simulation,practical engineering application and temperature load extremum calculation,etc.,to investigate the temperature variability of single-box multi-chamber box girder in different regions.The main results achieved are as follows:(1)Reveals the geographical variability of the measured temperature effects of single-box multi-chamber box girders in three regions.The geographical variability of temperature difference distribution form is not obvious,but there is obvious geographical variability of temperature difference representative value.The measured vertical temperature difference in the middle web of the box girder in the three regions is higher than the measured vertical temperature difference in the side web,and the measured transverse temperature difference in the sunny side of the top slab is higher than the measured transverse temperature difference in the sunny side of the bottom slab.The spatial distribution prediction model of "quadratic curve" of vertical temperature difference in the web of concrete box girder and the spatial distribution prediction model of "exponential curve of sunny side and sunny side" of transverse temperature difference in the top slab(bottom slab)are proposed,and the distribution law of temperature difference measured in the field based on the model in the three regions is The validity of the model is verified.(2)Based on the finite element theoretical model of the daylight temperature field of the single box and three chamber box girder,a formula for calculating the temperature difference of the section with the structural parameters as the independent variables was established.The environmental models include: atmospheric temperature calculation model,solar radiation model,and shading model.The solar radiation model and the shading model are implemented by different physical modules of the general finite element software COMSOL,and the validity and applicability of the finite element model are verified by the measured data in the field and the measured data in the existing literature.The sensitivity analysis of structural parameters is carried out by using finite elements according to the range of actual engineering design and construction parameters,and the formulae for calculating the vertical temperature difference of the web and the transverse temperature difference of the top and bottom slabs considering the thickness of the paving layer,the radiation coefficient rate,the height of the beam and the outreach length of the flange slab are proposed,which can quickly calculate the temperature difference of concrete box girder sections with different structural parameters.(3)Based on the measured meteorological data and structural temperature data in the field of the three models,the prediction formulae for the section temperature difference and effective temperature of box girder in three regions with meteorological parameters as independent variables are proposed.The predicted values are in good agreement with the field measured values,and the reliability and applicability of the temperature difference distribution model and section temperature difference prediction formula,as well as the effective temperature prediction formula,are further verified by relying on the Pesen Liujiang Special Bridge in Guangxi.The long-term(1955~2016)meteorological data of three provinces,Tibet,Shaanxi and Guangxi,were counted,and the long-term calculation statistics of temperature difference and effective temperature of concrete box girder in three provinces were obtained based on the section temperature difference prediction formula and effective temperature prediction formula,and the temperature action samples were obtained;based on the extreme value theory and temperature action data samples,the gradient of concrete box girder in three provinces with 50-year recurrence period was calculated Based on the extreme value theory and the temperature action data samples,the representative values of temperature load and uniform temperature load were calculated and the distribution maps of temperature action values were drawn.There is a significant geographical variability in the temperature action of concrete bridges.Among them,the maximum geographical variability of vertical temperature difference in the middle web is up to 10.5℃,the maximum geographical variability of transverse temperature difference in the sunny side of the top slab is up to 20.3℃,and the maximum geographical variability of effective temperature variation range is up to 20.8℃.