| Concrete arch bridge with stiffed concrete filled steel tube (CFST) has many characteristics such as long span, high load-carrying capacity, stability, and suitable for complex mountain canyon terrain. Therefore, this type of bridge has got the designers' favor at present. In order to ensure the safety and comfort of the train operation, the long-term deformation of the bridge should be strictly controlled. However, there are few reports on the long-term deformation research of such type of bridge. Therefore, the Beipanjiang reinforced concrete arch bridge with CFST with span of 445 m was taken as an engineering background.Then, an experimental research of the shrinkage and creep test of CFST under axial load was studied. The temperature field and long-term deformation behavior of the arch were exploded by experimental and theoretical methods. The main research contents, methods and research results are as follows:1. The differences of the formulas proposed by different researchers to calculate the solar radiation intensity, convection and radiation heat transfer coefficient of concrete girder temperature field were discussed by the meteorological parameters method. The reasonable formulas of the solar radiation intensity were chosed based on the calculation example. The convection and radiation heat transfer equations are simplified. The difference of differential equation and boundary condition to determain the concrete humidity and temperature field were compared. The ANSYS finite element program was used to analyze the concrete humidity field, and the correlation coefficients were given. The results show that the ANSYS temperature field module can predict the concrete humidity accurately based on the reasonable parameter values. (Chapter 2)2. The existing concrete shrinkage and creep experimental results explored in China were collected. The applicability of the common used shrinkage and creep prediction model was discussed. In addition, the advantages and disadvantages of the predicting models considering constant or varying temperature and relative humidity were analyzed. Based on collected experimental results and CEB10 model, the models for predicting the concrete shrinkage and creep under natural environment were proposed and verified. Those proposed models can take the varying temperature and relative humidity into consideration. And, high accuracy was observed in certain examples. By using the creep and swell algorithm of ANSYS, the ANSYS finite element program was used to calculate the long-term deformation of concrete structures under complex structure and boundary conditions. The time-dependent deformation results of prestressed concrete T-section beam and two-span concrete girder were used to verify the correctness of the method proposed in this paper. (Chapter 3)3. The experimental research on the temperature effect of the vibrating wire strain sensors was exploded. The correction formula of the free sensor, the sensor installed on the concrete and CFST shrinkage and creep members under natural environment were fitted. In addition,the shrinkage and creep tests of CFST under natural environment around the bridge site were carried out. The experimental results show that the shrinkage and creep strains of CFST are smaller than that of plain concrete. And the fully bonded assumption between steel and concrete was verified. Based on .the force balance condition, compatibility of deformation condition, the age-adjusted effective modulus method and step-by-step integration method,the formulas used to determain the long-term deformation of the CFST taking into the tight hoop force into consideration or not were deduced and the parameters were analyzed. The results demonstrated that the proposed formula is simple and accurate enough. If the concrete shrinkage and creep models considering the ambient conditions were used in the proposed formulas, the prediction accuracy can be improved. (Chapter 4)4. On the basis the concrete arch bridge model, the thermal behavior of the arch in finished state were measured. Besides, the long-term deformation, stress of concrete and steel tube of the arch were measured in construction and completion stage. The results show that the temperature field along the arch axis shows non-uniform distribution. The displacement and stress of the arch in main sections show cyclical changes characteric with time. Because of the concrete creep and shrinkage, the displacement of arch during the construction and completion stage, the concrete strain and steel stress gradually increase with time. And the long-term deformation effect of arch caused by shrinkage and creep of concrete can not be neglected. (Chapter 5)5. Based on the measured temperature field and the finite element meteorological parameters method, the characteristics of the arch girder were conducted. Then, several two-dimensional plane temperature field models with different boundary conditions along the arch were established; The non-linear temperature gradients along the height of the beam were transformed into the linear temperature gradient that can be used in the beam element of ANSYS. Therefore, the temperature effect of the arch can be calculated by the three-demensional beam element. Finally, the results were validated by three-demensional solid element. All the calculated results were compared with the experimental results. The results show that the finite element method can be used to analyze the temperature field and vertical temperature gradient of arch. The temperature stress and deformation of the section calculated by the three-demensional beam element are in good agreement with the measured results.(Chapter 6)6. Based on the collected parameters such as temperature, relative humidity, and rainfall at the bridge site, the computational modeling considering the construction process was conducted by structural analysis software ANSYS to calculate the temperature field and humidity field of the arch bridge. Therefore, the distribution characteric of temperature field and humidity field of the bridge were obtained. For calculating the arch time-dependent deflection, the temperature field and humidity field were simplified. In addition, based on the proposed concrete shrinkage and creep models considering the varying temperature and relative humidity and the ANSYS secondary development method, the long-term deformation of the arch bridge in the construction process and completion of the bridge were calculated.And all the computational results were in good agreement with those measured results. All in all, the method proposed in this paper can predict the concrete strain, steel stress and arch deformation accurately. (Chapter 7)... |
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