Theory And Application Study Of Sunshine Temperature Effects On Long-Span CFST Arch Bridge

In the recent 20 years, the concrete filled steel tube(CFST) arch bridge as a new kind of bridge obtained rapid development in our country, being lightweight structure, artistic modelling, strong spanning ability and convenience merits. But in theory, method, standard-setting and so on are still relatively backward, there are many issues to be studyed, temperature is one of the problems. CFST structure has different material composition and structural characteristics compared with ordinary concrete structure, temperature distribution and the temperature effects are also different between the twos. Being work related with temperature less and no standard related coming out, it is necessary to the temperature effect of CFST arch bridge for further study.In view of the status quo, from the installation of CFST steel arch ribs, concrete perfusion state and completed bridge state, studies based the engineering background of zhijing river CFST bridge-span 430m were done centering on sunshine temperature and the environment temperature, including temperature field distribution and temperature stress. This work are following:1. Edition and application of finite element program modules about temperature Field and its effects.According to the basic laws of heat transfer, solar physics, general astronomy and FEM theory, the finite element method of sunshine temperature and stress analysis method was establisheded and edited the program modulus of CFST arch bridge sunshine temperature effects. The utility and reliability of the computational model and procedures were verified comparison with experimental results.2. Research on temperature field and its effects of CFST steel arch ribs in installation phase.During erection of large span CFST arch rib, steel ribs lineshape and stress state were easily affected by sunshine and environment temperature under long Cantilever. Research on the temperature field distribution and temperature effects were deeply done. Research indicated that buckle Cable temperature variations and gradient temperature distribution are the main reasons. On this basis, this thesis fits the temperature distribution curve and proves a scientific basis for construction control through calculation and analysis.3. Research on temperature field and its effects of CFST steel arch ribs in concrete construction phase.After the closure of empty steel tube, the concrete which in steel tube must be pumped up. The whole steel tube arch ribs were subjected to not only sunshine temperature and environment temperature, but also concrete hydration heat. The sunshine effects and hydration process must be studied before considering the comprehensive influence of temperature.For composite cementitious material micro-expansion high strength concrete used in this project, hydration heat release process and its elastic modulus growth curve were analyzed.On the basis of the combined effects of sunlight and hydration heat, temperature distribution and its effects were studied. The results show that the concrete hydration heat released rapidly with adding the water reducer and high strength concrete expansion agent after the longer induction period, and the temperature rose rapidly, The temperature at the center reached the highest value 61℃, within 12 hours. There is large temperature difference between section center and outer edge, temperature difference between inside and outside reach to the maximum 31.3℃. During the hydration process in CFST, the interface tensile stress does not exist. Debonding phenomenon will not appear as to affect the steel concrete composite mechanical properties. During hydration period, the cross section maximum gradient of temperature is generally appear in the morning of 6 to 8 AM. Steel surface temperature stress can reach to maximum of 60MPa, concrete core compressive stress can reach to 6.8MPa.4. Research on temperature field and its effects of completed CFST arch bridge.To determine the values of CFST arch bridge temperature field, the calculation closure temperature of CFST and the effective maximum or minimum temperature were studied. According to the process of hydration heat temperature variation and elastic modulus variation, The study shows that for special concrete, the calculation closure temperature is depended on empty steel tube closure temperature and placing temperature, and the calculation closure Temperature can be taken as the average of the two temperature. In the clear sky sunshine, the maximum and minimum effective temperature can be obtained from the highest and minimum average daily temperature.The values of the gradient temperature has been studied also, through the analysis of three different tube diameters and wall thickness of CFST, Fitting the values of the temperature gradient curve. For the circular cross-section, the radial temperature gradient has directionlity, this gradient temperature can be called sun-direction radial temperature gradient.At the basis of the above, temperature effect and the stability of completed CFST arch bridge has been studied. Studies show that the influence of temperature load on the structure is important for the deflection and internal force, especially for the arch bridge foot. Being arch ribs are truss structure, the force between upper ribs and down ribs is not the same under temperature load, so the most unfavorable working cases are different between upper ribs and down ribs when calculate the temperature force. Still analysis show that not only uniform temperature but also gradient temperature must be considered, especiallyconsidering the gradient temperature for bending moment. The double nonlinear stability analysis of Zhijing Rive bridge shows that first and second stability factor reduced 20%-40% considering temperature load.