| The main arch of a concrete filled steel tube(CFST)arch bridge is composed of concrete poured into the steel tube.The thermal performance difference between the two materials,the size of the section and the sunshine environment of the bridge lead to the large temperature difference of the section,which leads to the structural deformation.The statically indeterminate characteristics of long-span CFST arch bridge constrains the structural deformation,and then produces temperature stress,which poses a threat to the structure.At present,the research on the temperature field of CFST is mainly based on the single tube and dumbbell-shaped cross-section of small and medium-span arch bridges.There are few studies on the truss-type cross-section used in long-span concrete-filled steel tube arch bridges.The consideration of mutual occlusion between structures is lacking,and the temperature field and temperature effect analysis of the cross-section under solar radiation occlusion are lacking.Meanwhile,the construction scale and number of the CFST arch bridge are still rising gradually.Therefore,it is of great significance to study the temperature effect of the long-span CFST arch bridge for the further development of this kind of bridge.In this thesis,through the actual test combined with finite element simulation,the temperature field of the main arch section of the long-span CFST arch bridge is studied,and on this basis,the typical temperature gradient conditions of the main arch section under sunshine are compared and analyzed,and the significance of the factors affecting the temperature of the section is compared.Firstly,based on the heat conduction theory and differential equation,under the applicable boundary conditions of the CFST member,the solution method for temperature field of CFST is introduced.Then the astronomical and heat transfer parameters related to the calculation of boundary conditions are introduced.After that,combined with the materials used in the project,the heat conduction parameters are calculated,and the temperature field model of single tube is established by using ANSYS(finite element software).The reliability of simulating the daily temperature change of single tube was verified by comparing the measured temperature field of single tube in the test with the finite element simulation results.Based on the simulation of daily temperature variation of a single pipe,a finite element model of temperature field for truss arch section is established by using the algorithm of computer graphics,and the reliability of the algorithm is proved by comparing the test results of real bridge with the finite element simulation results.By comparing the calculated results of temperature field in summer and winter,it is pointed out that the influence of cross-occlusion effect on temperature field in summer is more obvious.Then,the influence of mutual occlusion effect on the location of the same measuring point in the lower chord of each characteristic section is compared,and it is pointed out that the temperature variation amplitude and the overall size of the temperature curve caused by the mutual occlusion effect of the structure are positively correlated with the truss height.Then,the simplified method of section temperature gradient is proposed by using the established section temperature field model of truss main arch.By extracting the simplified temperature gradient of each characteristic section of the main arch when the structural mutual occlusion effect occurs,the full-bridge model under various working conditions is established.The influence of temperature gradient condition and standard condition on the internal force and stress of the structure is compared,and it was pointed out that it was the most unfavorable to the structure when the arch foot to the 1/8 L range of the main arch appeared unilateral mutual occlusion for the second time.Finally,the orthogonal test with eight factors and four levels was set up by using the finite element model,and to distinguish the significance of the factors affecting the peak temperature and temperature gradient at the top of tube section,and to analyze the influence of various factors on the test results.Absorption coefficient,wind speed and atmospheric transparency have significant effects on peak temperature and cross-sectional temperature gradient.In addition,the structural azimuth also has a significant impact on the temperature gradient of the section.In areas with good air quality and low wind speed in China,the cross-sectional temperature changes significantly under sunshine,which can be adjusted by selecting surface coatings with small radiation absorption coefficient. |
