| Sichuan to Tibet railway is under construction in China,in which bridges account for a large proportion.With the advantages of rigidity,durability and economy,the demand of CFST arch bridge in highway and railway in Tibet plateau area are increasing sharply.Temperature calculation theory is an important part of the design theory of CFST arch bridge.At present,most of the relevant researches used the numerical simulation method to analyze the concrete-filled steel tubular arch bridges in plain area.There were some problems in the results,such as not considering the climate characteristics of Tibet Plateau,not considering the applicability of large-span conclusions,and lack of sufficient test data validation.Therefore,the temperature field and temperature effect of the steel tube concrete arch bridge in the plateau area was studied based on Zangmu Bridge,which is the largest steel tube concrete arch bridge in the world.On the basis of summarizing the research status and deficiencies at home and abroad,the following work had been completed:1.Study on the climatic characteristics of TibetTaking Shannan City,where Zangmu bridge is located,as an example,the climatic characteristics of Tibet Plateau were studied.It was found that the climate in this area was characterized by low annual average temperature,small annual temperature change,large daily temperature change,strong solar radiation,long sunshine time,less precipitation and strong wind power.Combined with the local measured temperature,the annual temperature change function and the extreme daily temperature change function were obtained,which provided the extreme temperature boundary conditions for the analysis of the temperature problem of the arch bridge in Tibetan.2.Research on the temperature field test and prediction model of concrete filled steel tube hydration.The hydration temperature field of concrete-filled steel tubes with different diameters at low temperature were tested in a constant temperature test box.The results showed that the hydration heat of CFST had the characteristics of mass concrete;the larger the diameter,the greater the temperature rise of core concrete,the greater the temperature difference between the inside and outside,and the smaller the cooling rate.The test of the hydration heat field in the real bridge verified the characteristics again.Comparing the hydration heat field results in the of the real bridge and the temperature box,it was found that the sunshine and high temperature in summer would cause a higher hydration temperature difference than that in winter.It was suggested to avoid the construction under the high temperature in summer.According to the test and finite element analysis results,the theoretical prediction model of hydration temperature & internal and external temperature difference of large diameter concrete filled steel tube were proposed,and their accuracy were verified by comparing with the test results in literature.Based on the analysis of the prediction model,the calculation method of the best time of concrete pouring in the pipe and the relevant measures for winter construction were proposed.The researches solved the technical problem that it was difficult to determine the time-varying law of hydration heat in concrete filled steel tube under the influence of multiple factors.It had a strong reference and guiding significance for concrete-filled steel tube arch bridge construction in different environment,especially in plateau climate conditions.3.Research on the sunshine temperature field test and temperature load calculation parameters of arch rib in Tibet.The long-term continuous sunshine temperature field test and real bridge sunshine temperature field test were carried out in Tibet.The test was one of the most complex,data and longest time temperature field tests in the same kind of tests at home and abroad.The results showed that the sunshine temperature field distribution of the main arch presented nonlinear characteristics.The internal temperatures of the main arch section changed little with the daily temperature,and the average temperature of the main arch section was closer to the daily average temperature,which had a large difference with the air temperature.Based on the statistical analysis of a large number of experimental data,it was considered that the closure temperature of concrete-filled steel tubular arch bridges in Tibet was mainly calculated by software,and the standard calculation formula was still applicable;the maximum effective temperature was suggested to take the daily average temperature plus 2℃ on the hottest day,the minimum effective temperature was suggested to take the daily average temperature minus2℃ on the coldest day;gradient temperature difference between the upper and lower chords of truss main arch did not exist,and the temperature effect could be ignored;the influence range of daily temperature difference of single pipe was recommended to be 25 cm,and the maximum temperature of upper and lower edge of section is 16 ℃ and 10 ℃ respectively.The gradient temperature difference effect of single pipe was large and cannot be ignored.Based on the principle of difference method,a special analysis program for temperature field of concrete filled steel tube arch rib was compiled,and its accuracy was verified by comparing with the refined analysis results of ANSYS.The research results could supplement and revise the regulations in Chinese code,wich were related to the design and calculation of temperature effect of CFST arch bridge.4.Study on temperature effect of CFST arch bridge in Tibet and calculation method analysisBased on the temperature load calculation parameters proposed in this paper,the common model and the complete model including the arch seat were established for calculation and analysis respectively.Comparing with the test value of the real bridge,it was considered that the calculation results by using suggested temperature parameters and complete model including the arch seat was more accurate.Therefore,the temperature effect calculation method based on the temperature load calculation parameters and optimization calculation model proposed in this paper was proposed.The method could solve the technical problems that it was hard to verify the rationality of the temperature load calculation parameters and the accuracy of the temperature effect.It provided a strong support for standardizing the design and calculation of temperature effect in long-span CFST arch bridge under the climate conditions in Tibet Plateau.Finally,the influence mechanism and law of the stiffness ratio between the main arch and the arch seat on the temperature effect of the CFST arch bridge are preliminarily analyzed.It was pointed out that the stiffness ratio of the main arch and the arch seat was the main reason affecting the calculation results of the temperature effect. |
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