Research On Distortion Effect Of Composite Box Girder With Corrugated Steel Web And Steel Bottom Plate

With the widespread use of concrete box girder bridge in various traffic routes,the distortion analysis theory of ordinary concrete box girders has become relatively mature.However,concrete box girders are not economical because of their heavy weight and the large proportion of the dead load in the internal force of the control section.The corrugated steel web is used to replace the concrete web to form an original composite box girder with corrugated steel web,the self-weight is reduced,but the distortion bearing capacity of the box girder is also greatly weakened.In order to further reduce the self-weight,a steel bottom plate is used to replace the concrete bottom plate of the original composite box girder with corrugated steel web.The formed composite box girder with corrugated steel web and steel bottom plate effectively prevents the cracking of the concrete bottom plate in the positive bending moment zone of the original composite box girder with corrugated steel web.Although the distortion problem of original composite box girder with corrugated steel web and composite box girder with corrugated steel web and steel bottom plate is relatively prominent,the research on the distortion effect of the original composite box girder with corrugated steel web is very limited.And there is virtually no research on the distortion effect of composite box girder with corrugated steel web and steel bottom plate.Therefore,it is urgent to apply the existing relatively mature distortion theory to the composite box girder with corrugated steel web and steel bottom plate in this paper,the distortion effect of composite box girder with corrugated steel web and steel bottom plate is studied.(1)Firstly,the mechanical properties of corrugated steel web are studied.And the concrete top plate is equivalent to a flat steel top plate according to the principle of constant internal and external bending stiffness.The corrugated steel web is equivalent to orthotropic flat steel web based on the principle of constant shear force and equal shear strain.Finally,the composite box girder with corrugated steel web and steel bottom plate is equivalent to a steel box girder.Then,it is proposed to consider the constraint effect of the top and bottom plates on the corrugated steel webs according to the Saint Venant principle.Based on the energy variational method and the plate element frame method,the distortion analytical theory of the trapezoidal composite box girder with corrugated steel web and steel bottom plate is derived in detail.The correctness of the distortion analytical formula obtained in this paper is verified by comparing numerical examples with existing literature and finite element method.(2)The apparent elastic longitudinal modulus of the corrugated steel web used in the current composite structure bridge in our country is not more than 2% of the elastic modulus of the flat steel plate.The distortion warping normal stress of the web within the range not affected by the constraints of the top and bottom plate can be ignored.The apparent elastic modulus and effective shear modulus are close to those of a flat steel plate.If the concrete bottom plate of the original composite box girder with corrugated steel web is also equivalent,the distortion analysis theory set out in the present paper is also applicable to this type of composite box girder.According to the method in this paper,the constraint effect of the top and bottom plates on the web is taken into consideration,and the obtained results are more consistent with the finite element solution.The Krylov function is utilized to express the solution of the distortion control differential equation under the load of the full-span uniformly distributed distortion moments,which can simplify the form of the solution.The distortion warping normal stress on the steel bottom plate is much greater than the distortion warping normal stress on the concrete top plate.(3)Transforming the material of the bottom plate or web and cross-sectional size,from ordinary concrete box girder to original composite box girder with corrugated steel web,and then to composite box girder with corrugated steel web and steel bottom plate,distortion warping stiffness and transverse frame stiffness in sequence significantly weakened.The maximum distortion and warping normal stress of the original composite box girder with corrugated steel web is nearly twice that of the ordinary concrete box girder,and the maximum distortion and warping normal stress of the composite box girder with corrugated steel web and steel bottom plate can reach more than ten times that of the original composite box girder with corrugated steel web.(4)The distortion and warping normal stress of the concrete top plate can be reduced by setting the web depression angle,and attention should be paid to the increase of the distortion and warping normal stress of the steel bottom plate under the action of the concentrated distortion moment caused thereby.When considering the influence of beam height on the distortion effect of composite box girder with corrugated steel web and steel bottom plate,attention should be paid to the types of distortion loads.As the thickness of corrugated steel webs increases,the maximum distortion warping normal stress on the steel bottom plate and the maximum distortion warping normal stress under the action of uniformly distributed distortion moments decrease more significantly.