Analysis Of Torsional Characteristics Of Composite Girder Bridge With Steel Truss Webs

Since the 21st century,China’s infrastructure construction has developed rapidly,and great achievements have been made in the field of bridge engineering.However,the increasing traffic volume and the complex and changeable construction environment also put forward new and higher requirements for bridge construction in the future.Composite girder bridge with steel truss webs is a relatively new type of steel-concrete composite girder bridge that has emerged since 1980 s.This new type of bridge structure has the advantages of light dead weight,large overall stiffness,strong wind resistance,good buckling deformation resistance and effective avoidance of web cracking,etc.and its application in bridge construction is gradually increasing.Therefore,it is necessary to study its mechanical properties in depth.In view of the lack of research results on such structures in China at present,the torsional mechanical properties of such composite girder bridges are studied with the engineering background of "Nanjing Crossing Highway--Jiangshan Bridge",the first composite girder bridge with steel truss webs that has been completed and opened to traffic in China.The main research contents are as follows:(1)Because of the steel girder truss in the discontinuity of the bridges on the longitudinal section,bring great difficulties to the theoretical analysis of such structure.Referring to Academician Li Guohao’s method for torsion analysis of space steel truss bridges,used the principle of stiffness and displacement equivalence the girder structure of steel truss girder is equivalent to the orthotropic plate webs,Then the composite girder bridge with steel truss webs can be equivalent to a thin-walled box girder structure with orthotropic webs.Based on the Wumansji second torsion theory the free torsion and constrained torsion of equivalent box girder of this kind of composite girder bridge are analyzed.(2)An example of a two-span steel-truss girder bridge with concrete composite girder is taken to analyze the geometrical characteristics of its equivalent section.The finite element analysis model of the composite girder bridge and its equivalent box girder in this case was established by using ANSYS18.2 finite element simulation software,and the finite element analysis model was contrasted and analyzed by using the deflection theory of box girder considering shear deformation.Based on the analysis method of free torsion and constrained torsion of equivalent box girder,the torsion stress of equivalent box girder of steel truss girder and concrete composite girder is solved,and the calculation results are verified by using the spatial finite element analysis model.(3)Analyses the partial load effect of composite girder bridge with steel truss webs,in a simply supported composite girder bridge with steel truss webs on the space finite element analysis model respectively symmetrical loading and eccentric loading,finite element analysis to extract a 10 cent point each cross section on one side of the eccentric load floor normal stress of concrete and the steel girder central diagonal shear stress,and calculated the stress magnification coefficient;The effects of structural parameters such as height of composite beam,wall thickness of steel truss girder,outer diameter of steel truss girder and width of cantilever plate on partial load effect of simply supported composite girder bridge with steel truss webs are discussed.(4)By using the Wumansji torsion theory and the research results of bridge structure dynamics,the restricted torsional vibration frequency calculation formula of equivalent box girder of simply supported composite girder bridge with steel truss webs under free vibration state is analyzed and derived,and the correctness of the calculation formula is verified by finite element model.Analyzes the diaphragm plate number,span of composite beam,height of composite beam,steel truss web steel truss webs outer diameter and wall thickness,the cantilever plate width of simply supported steel concrete composite girder bridge girder abdomen constraints the influence of the torsional vibration frequency.