Analysis On Torsion And Distortion Effect Of Concrete Composite Box Girder With Steel Truss Webs

Steel truss web concrete composite box girder is a relatively new type of steel-concrete composite box girder structure,which has the advantages of light weight,convenient site construction,avoiding web cracking,good permeability and beautiful bridge type.At present,scholars at home and abroad have carried out more in-depth research and Exploration on the mechanical characteristics of the structure,but there is relatively little research on torsion and distortion.In this paper,through theoretical research and finite element simulation analysis,the torsion and distortion of steel truss web concrete composite box girder are preliminarily studied.The main contents are as follows:(1)According to the principle of equal shear deformation,the webs of steel truss in composite box girder are equivalent to steel webs,and the webs are transformed into continuous system.Based on the theoretical calculation method of torsional geometric characteristics of thin-walled box girder,the expressions of torsional geometric characteristics of cross section of composite box girder,such as torsional center,main sector coordinate,main sector moment of inertia,are derived.The influence of horizontal inclination angle of steel truss web member in cross section on torsional Center,main sector moment of inertia and main sector coordinate is analyzed.The results show that the distance between the torsion center and the roof center increases with the increase of?,and the main fan moment of inertia decreases with the increase of?.(2)Starting from the free torsion of steel truss web concrete composite box girder,the free torsion inertia moment I_d of composite box girder is deduced.??is used to express the degree of freedom of warping displacement of composite box girder in restrained torsion,and the expressions of warping stress of concrete top and bottom slab and converted steel web of composite box girder in closed section are derived.Then the differential equation of restrained torsion control of composite box girder is derived,and the differential equation is solved by the initial parameter method.Finally,the influence of the width to height ratio of the cross section and the horizontal inclination angle of the steel truss web member in the cross section on the torsional warping normal stress of the composite box girder,and the parameter analysis of the warping normal stress of the three kinds of box girder under the different ratio of the suspension wing are carried out.The results show that after the height width ratio of the composite box girder section exceeds 1.0,the warping stress at the three control points decreases steadily with the increase of the height width ratio,and the decrease becomes smaller;the change of the horizontal inclination angle of the steel truss web member in the cross section has little effect on the warping stress of the cross section at the middle of the span;the torsional warping normal stress of the square box girder is the most sensitive to the change of the cantilever ratio.(3)Ignoring the shear deformation of the cross section,the total potential energy expression of the composite box girder is derived by the principle of minimum potential energy standing value,and then the differential equation of distortion control is derived by the variation method,and the differential equation is solved by the initial parameter method.Finally,the influence of the horizontal inclination and the ratio of height to span on the warping normal stress of the composite box girder is analyzed.The results show that when the angle is about 15°,the distance from the distortion center to the roof increases,and the increase is more stable before the angle is 15°.When the beam span and other dimensions remain unchanged,the height of the box chamber increases,and the distortion warpage normal stress in the middle of the span decreases.(4)According to the theoretical calculation method deduced above,the torsion warping normal stress and distortion warping normal stress of the web member and the top plate connection point,the left end point of the top plate and the connection point of the web member and the bottom plate at the distance of 2m from the midspan section and 3/8l cross section of the steel truss web concrete composite box girder are calculated respectively,and compared with the finite element calculation results.The results show that the warping normal stress obtained by the analytical solution is basically consistent with the change trend of the normal stress obtained by the finite element calculation,all of which are antisymmetric distribution,and the stress of the bottom plate is relatively close,but the stress box difference of the top plate at 2m from the midspan section is large,which is caused by the stress concentration.