Analysis On Temperature Field And Temperature Effect Of Concrete Box Structure

In recent years, with the increase of bridge span, the box structure, such as the tallpylon, hollow thin-wall pier and thin-walled box girder and so on, is more and morewidely applied. Meanwhile, differential temperature stress and temperature cracking inthe concrete box structure become increasingly prominent. Through investigation, athome and abroad, bridge structures damaged by temperature stress are not in theminority. In addition, the structure maintenance cost caused by temperature stress is ashigh as one million yuan. Under the above background, taking the concrete box girderbridge as the research object, the paper researches the box girder temperature field andtemperature under the effect of solar radiation. The main research contents include:①Studying calculation model of concrete box structure thermal physicalparameterUsing the triangle of the sun and structure surface, establish relationship betweenparameters including location, date and time epoch of the structure surface and the sundirect radiant energy. Based on this, deduce the calculation model of the sky radiation,solar radiation and sky radiation reflection, atmospheric counter radiation andcomponents reflection.With the concept of the radiation temperature, transform the second kindboundary condition into the third kind boundary condition. On the basis of heatexchange balance, establish the relationship between structure surface radiationtemperature and parameters including atmospheric temperature, radiation energy,absorption coefficient of components and so on. By the third kind boundary condition,obtain the relationship between structure surface temperature and radiation temperature,heat-flow density.②The study of concrete box temperature field calculation modelBased on the basic equation Ti=f (x, y, z,t)of heat conduction, the relationshipbetween the boundary temperature and time, flux and time, heat flux and temperaturedifference are deduced. Starting from the calculation accuracy and computationalcomplexity, compared the respective features of the Fourier heat conduction equation,the approximate calculation method and half experience and half theory formula.Using numerical simulation software ABAQUS to establish two-dimensional transient temperature field analysis model, impose the thermal boundary condition and analyzetemperature field. The temperature distribution of box girder cross section at any timeis got and compared with the measured temperature, verify the validity of thenumerical simulation.③The study of the concrete temperature effect analysis theory and methodThe basic assumptions of temperature distribution along the vertical line of thebridge, isotropic of concrete material and in line with the linear elastic deformation lawhave been made. On the basis of ε=α T, this paper derived the calculation formula ofthe stress and secondary stress of concrete box girder. Using the principle ofsuperposition, continuous box girder structure total calculation formula of temperaturestress has calculated.With Niu Lang river bridge in Yunnan as an example, the wholebridge model is established using the finite element analysis software and get thetemperature effect of key sections when the whole bridge under the temperaturegradient loads.