| Concrete-filled steel tubular(abbreviated as CFST)arch bridge is constantly applied in Railway engineering by virtue of its own advantages,especially with the railway construction center gradually moving to the western region,the development of the super-large railway bridge has been greatly promoted.However,most of the research objects are focused on highway bridges and railway bridges with small and medium span,and few researches are focused on Super Long Span CFST railway arch bridge with main span over 400 m.The recommended parameter value in the Technical code for concrete-filled steel tube arch bridges is not generally suitable for long-span CFST arch bridge,and there is a large hysteresis.Based on the above problem,the paper takes a 400 m scale CFST railway arch Bridge as project background,and the following research is carried out around the reasonable range of design parameters,then a new model is constructed to verify the rationality of the model according to the optimized parameters which can provide guidance and suggestions for similar bridge design in the future:Firstly,the paper develops the spatial finite element analysis model by Midas/Civil2015.At the same time,in order to verify the rationality of the model,the command flow is compiled to establish the ANSYS model for comparison.The paper compares the first ten natural vibration characteristics and modal shapes between the two models,the results show a high degree of agreement,which also verify the rationality and authenticity of Midas/civil model,and establish the foundations for subsequent research work.Secondly,the stress and deformation of the main girder and arch rib in the CSFT arch bridge model under the most unfavorable load combination action of dead load,live load and additional force is analyzed.In addition,according to the analysis of dynamic characteristics of the structure,the vibration modes and corresponding natural frequencies of the bridge are determined.The response spectrum and time history analysis are used to analyze the displacement and internal force response of each key section,so as to verify the two methods each other.Then,the influence of traveling wave effect on this kind of 400 m scale railway CFST arch bridge is also considered.The results show that the force of the structure is very complex,the frequency spectrum is dense and the vibration mode is diverse.Under the action of static load,the internal force and deformation of arch foot and mid span section are greater than others.The maximum natural frequency of the first eight modes of the bridge is 1.1404 Hz,which belongs to a partial flexible structure,and the first two modes of the bridge show transverse bending.The bearing capacity of the structure to the transverse seismic action is much weaker than the other two.Moreover,the variation law of seismic wave is various under different wave velocities,and the structure is more sensitive to low wave velocity within 500m/s.Although there are some differences between the response spectrum method and the time history analysis method,the response peak values and variation rules between the response spectrum method and the time history analysis method are basically consistent.Thirdly,based on the static and dynamic characteristics of the structure and the seismic response analysis,it is found that the weakness of lateral stability and local stress are very prominent.The arch rib inclination angle,transverse brace and the diameter thickness ratio of steel pipe are selected for multi index analysis and optimization.Based on various factors,it is suggested that the reasonable range of leaning angle is 3.5～4°;For the transverse brace,it is suggested that the tangential brace should be arranged in the span from 1L/4 to 3L/8 of the arch rib,and then the “一” shaped brace which is more convenient for construction can be selected at the mid span section,the tangential brace should be arranged at the1L/8 span,and then the “米” shaped brace should be arranged near the arch foot.When selecting the steel pipe size of this kind of 400 m scale railway CFST arch bridge,it should be given priority to increase the thickness of steel pipe.On this basis,if the structural performance can not be guaranteed,,the outer diameter of steel pipe should be continuously increased at the arch foot to improve the stress problem,so as to ensure the structure has sufficient redundancy.Fourthly,on the basis of the original model,a new CFST arch bridge of super long span railway is constructed by using the optimized parameters.At the same time,the rationality of the CFST arch bridge is verified by the structural stability safety factor which is the most commonly used in practical engineering.The results show that although the direction of each order instability mode of the two models does not change under different working conditions,the structural stability safety factor of each order of the optimized model is significantly improved compared with the original model. |
