Study On Torsional Effect Of Composite Girders With CSW-CFST Truss Chords

Composite girders with corrugated steel webs and concrete-filled steel tubular(CSWCFST)truss chords is a new steel-concrete composite structure proposed to meet the requirements of bridge width,which has attracted widespread attention because of its good force performance.The composite girders with CSW-CFST truss chords belongs to a light composite structure,and the torsional effect under eccentric load is obvious,but the current research on the torsional effect is still in the development stage.Combined with simulation examples and practical engineering,this paper uses a combination of theoretical analysis and numerical analysis to study the torsional effect of composite girders with CSW-CFST truss chords,the main contents are as follows:(1)According to the structural characteristics of composite girders with CSW-CFST truss chords,the components are equivalent.Considering the material differences,the concrete roof plate is equivalent to a thin-walled steel plate;The shear of the corrugated steel web is equivalent to a flat steel plate that only bears the vertical shear force,and the shear flow is evenly distributed along the cross-section;Steel tubular concrete is equivalent to a chord that only bears the normal stress of warpage.The finite element model was established to analyze the force characteristics of the truss under bending torsional load,and the calculation formula of the shear equivalent thickness of the warren,X-shaped,N-shaped and K-shaped trusses was derived based on the energy principle,and the flat-linked trusses that were originally discrete structures were transformed into thin steel plates of uniform and equal thickness along the longitudinal direction of the bridge,so as to convert the entire composite beam section into a special thin-walled beam section.(2)Based on Umanski’s second theory,the differential equation of constrained torsion of simple supported beams in the elastic stage is derived,the analytical solution under typical load is obtained by using the initial parameter method,and the calculation method of geometric characteristic parameters is discussed.The distribution law of torsion angle,deformation coefficient,torsional double torque and warpage torque of the composite beam along the beam length under the action of two working conditions is given by example.The positive stress and shear stress of torsional warpage constrained by the span section,as well as the torsion angle of the composite beam and the axial force of the lower chord were calculated,and compared with the finite element results,the two results were in good agreement and verified the accuracy of the formula.(3)Based on the composite girders with CSW-CFST truss chords as the research object,ABAQUS is used to carry out finite element simulation analysis.The distribution of deflection,torsion angle and stress amplification coefficient under eccentric load was studied.The influence of cross-section design parameters on torsional performance was studied: changing the thickness of the corrugated steel web and the wall thickness of the lower chord steel pipe had little effect on the eccentric load effect.Increasing the high span ratio is conducive to reducing the positive stress,but the stress amplification coefficient shows an increasing trend.Increase the wide span ratio,the positive stress and stress amplification coefficient of the loading side under eccentric load have a tendency to increase,the increase of the cross-section width leads to the increase of eccentricity,and the transverse stiffness of the cross-section is low,resulting in distortion effect,in the actual project,attention should be paid to controlling the transverse width of the truss,while strengthening the transverse stiffness of the crosssection;Setting the K-shaped cross connection can well reduce the torsion angle of the section and increase the torsional stiffness of the section.Therefore,in the actual project,it is appropriate to increase the number of K-shaped horizontal links.