Research On Torsion And Distortion Effects Of Single-box Multi-cell Composite Box Girder With Corrugated Steel Webs And Steel Bottom Plate

The composite box girder with corrugated steel webs and steel bottom plate is based on the traditional composite box girder with corrugated steel webs,the concrete bottom plate is replaced by steel bottom plate with stiffeners,so as to form the composite box girder with corrugated steel webs-steel bottom plate-concrete top plate.As the thickness of the bottom plate of this kind of box girder becomes thinner,the torsional stiffness and distortion stiffness of the box girder will also decrease.Under eccentric load,the torsion and distortion deformation of the box girder are more obvious,especially for single-box multi-cell box girders,the increase of section width leads to more significant load effect.In addition,for the curved box girder with corrugated steel webs and steel bottom plate,the deformation of this type of box girder under eccentric load further increases due to the influence of curvature radius,and the torsion and distortion effects of the box girder must be paid attention to.Based on the existing research results,combining with the structural characteristics of the composite box girder with corrugated steel webs and steel bottom plate,the torsion and distortion analysis theory suitable for this type of box girder is put forward in this paper,and the correctness of the proposed theory is verified by model test and finite element analysis.The main research contents and conclusions of this paper are as follows:(1)Test and finite element analysis of single-box multi-cell composite box girder with corrugated steel webs and steel bottom plate.For single-box twin-cell model beam with equal cross-section,referring to the pure torsional loading device in the existing literature,a test scheme suitable for pure torsion of a model beam was designed.The torsional stress of each measuring point on the main test cross-section was obtained by loading the model beam in stages.At the same time,the finite element software ANSYS was used to establish the finite element model of the model beam.By simulating different loading conditions,the stress distribution law on the finite element model was analyzed,and the theoretical torsional stress value of each measuring point was compared with the finite element value.The comparison results showed that the measured stress value of the same measuring point was in good agreement with the finite element value,and the overall change law was consistent.The correctness of the finite element model was verified.(2)Analysis of torsion effect of single-box multi-cell straight box girder with corrugated steel webs and steel bottom plate.Considering the effective elastic modulus of each part after cross-section conversion,based on Ummansky’s second theory,the free torsion and constrained torsion of single-box multi-cell box girder are analyzed respectively,the constrained torsion differential equation of single-box multi-cell box girder is established,and the formula for calculating the constrained torsional stress for single-box multi-cell box girder is derived.For two numerical examples,the torsional geometric characteristics of single-box twin-cell and single-box three-cell box girder sections are calculated respectively,and the torsional stress distribution law on the cross-section of the two types of box girder are obtained.By comparing the composite box girder with corrugated steel webs and steel bottom plate with the traditional composite box girder with corrugated steel webs,it can be seen that the torsional stiffness of the composite box girder with corrugated steel webs and steel bottom plate decreases by 8.58%,and the cross-section constraint coefficient decreases by 58.44%.The effect of diaphragms and stiffeners on the effective torsional stiffness of composite box girder with corrugated steel webs and steel bottom plate are very small and can be ignored.Under the action of concentrated load and uniform load respectively,the variation trend of torsional displacement and internal force along the longitudinal direction is different,and the symmetric form of the same torsional displacement and internal force about the mid-span section is consistent.(3)Analysis of distortion effect of single-box multi-cell straight box girder with corrugated steel webs and steel bottom plate.Considering the different material properties of the top and bottom plates of box girder and the effective shear modulus of each part after cross-section conversion,the distortion differential equation of the single-box multi-cell box girder is established by using the plate girder-frame method and displacement method,and the calculation formula of the distortion stress of the single-box multi-cell box girder is derived,and the initial parameter solutions of distortion displacement and internal force considering the action of inner diaphragm are obtained.For two numerical examples,the distortion geometric characteristics of single-box twin-cell and single-box three-cell box girder sections are calculated respectively,and the distortion stress distribution law on the cross-section of the two types of box girder are obtained.By comparing the composite box girder with corrugated steel webs and steel bottom plate with the traditional composite box girder with corrugated steel webs,it can be seen that the distortion warping stiffness of the composite box girder with corrugated steel webs and steel bottom plate decreases by 38.89%,and the distortion frame stiffness decreases by 71.84%.The distortion displacement and internal force change of box girder along the longitudinal direction are different with the different number of diaphragms arranged in the span.The diaphragms have obvious inhibition on the distortion of box girder.Under the action of concentrated load and uniform load respectively,the variation trend of distortion displacement and internal force along the longitudinal direction is different,and the symmetric form of the same distortion displacement and internal force about the mid-span section is consistent.(4)Analysis of torsion effect of single-box multi-cell curved box girder with corrugated steel webs and steel bottom plate.Based on the stress characteristics of curved beam,the basic differential equation of curved beam is derived in detail,the bending-torsion coupling effect of curved box girder is introduced in essence,and the relationship between displacement and internal force of curved box girder is determined,the constrained torsional differential equation of single-box multi-cell curved box girder is established,and the initial parameter solution of torsional displacement and internal force considering the influence of curvature radius is derived.For two curved box girder examples,according to the obtained torsional geometric characteristics,the distribution law of torsional stress on the cross-section of the two types of box girders are obtained.By comparing the torsional properties of straight box girder and curved box girder,it can be seen that under the action of pure torque,the torsional displacement and internal force of curved box girder are little different from that of straight box girder.With the increase of curvature radius,both the mid-span torsional angle and the mid-span torsional bi-moment of the box girder decrease.Under the action of concentrated and uniform load respectively,the torsional displacement and internal force of the box girder show different trends along the longitudinal direction.(5)Analysis of distortion effect of single-box multi-cell curved box girder with corrugated steel webs and steel bottom plate.By analyzing the force of the box girder,the relationship between the curvature of the box girder and the distortion angle is established,and according to the distortion angle generated by external load and distortion warping stress,the distortion differential equation of the single-box multi-cell curved box girder is established,which is solved by the analogy method for beam on elastic foundation.The calculation method of equivalent distorted moment load equivalent to multiple concentrated loads is proposed,and the corresponding calculation formula is given.For two curved box girder examples,according to the obtained geometric characteristics of distortion,the distribution law of distortion stress on the cross-section of the two types of box girders are obtained.By comparing the distortion performance of the straight box girder with that of the curved box girder,it can be seen that the distortion displacement and internal force of the curved box girder are obviously different from that of the straight box girder.With the increase of curvature radius,both the mid-span distortion angle and the mid-span distortion bi-moment of the box girder decrease.Under the action of concentrated and uniform load respectively,the distortion displacement and internal force of the box girder show different trends along the longitudinal direction.