Study On Truss-Box Equivalent Theory Of Composite Truss Continuous Bridge With Steel Truss Webs

Composite truss web continuous girder bridge is a new type of composite structure bridge in recent years.It is developed from the traditional composite box girder bridge.It has the advantages of light weight,convenient construction,beautiful appearance and high spatial utilization rate.However,the discontinuity of the whole composite truss web continuous girder bridge leads to the assumption that the plane section of the longitudinal strain of the roof and floor is not established,so that the whole section cannot be calculated by a single beam element.At the same time,the stress of the steel truss and concrete connection is complex,and the existing calculation method is low precision and very cumbersome.All these factors limit the development of the new composite structure bridge.In order to promote the development and application of composite truss web continuous girder bridge in China,this thesis attempts to provide a scientific and effective equivalent theory,simplify the complex composite truss web continuous girder bridge into box girder model,and carry out finite element verification and other mechanical properties.Therefore,this thesis studies the following aspects:(1)The truss-box equivalent theory of composite truss web continuous girder bridge is proposed.The ABAQUS finite element model of composite truss web continuous beam bridge is established according to the actual project,and the truss-box equivalent theory of composite truss web beam bridge is applied.Taking the inclined web member as the main research object,the thickness of steel web is converted according to the condition of equal strain energy before and after deformation.Based on the principle of equal shear strain and shear force,the calculation formula of converting steel web to concrete web is deduced,and the truss-box equivalent theory based on continuous beam structure is proposed.(2)Study on bending performance of composite truss web continuous girder bridge.Based on the equivalent theory,the warping displacement function of shear lag is selected,and the shear lag theory of thin-walled beam and the energy variation principle are combined to establish a reasonable theoretical model for the shear lag effect analysis of composite truss web continuous beam bridge.The shear lag effect,vertical deflection and axial force calculation formula of inclined web bar of composite truss web continuous beam bridge under three typical load conditions are analyzed,and the influence of different load parameters on the shear lag of composite truss web continuous beam bridge is considered.(3)Study on shear performance of composite truss web continuous girder bridge.In this thesis,any infinitesimal element on the equivalent box girder section is taken as a unit to analyze the size and distribution of shear stress under different load conditions,and then the shear distribution rate of composite truss web continuous girder bridge is studied.The shear analysis of box girder converted to concrete web is carried out to obtain the shear distribution rate relationship,which mainly considers the relationship between inclined web bar and shear distribution rate of concrete under three typical loads of composite truss web girder bridge and considers the influence of lateral position of load on shear lag.(4)Study on torsional distortion performance of composite truss web continuous girder bridge.In this thesis,the composite truss web continuous beam bridge is equivalent to the equivalent box girder.Through the finite element verification of the composite truss web continuous beam bridge before and after the equivalent,the rationality of the equivalent theory is further verified.Through the control variable method,the factors that may affect the torsional distortion performance are simulated and compared.The influence of pier height,diaphragm density and thickness on the torsional distortion performance of the composite truss web continuous beam bridge is explored,which provides an effective and reliable theoretical basis for engineering practice.(5)Verification and analysis based on finite element model.In this thesis,ABAQUS finite element software is used to establish the finite element model according to the actual engineering bridge drawings,and the relevant verification of the finite element is carried out through the full text according to the different research contents of each chapter.The finite element verification results show that the theoretical value of the equivalent theory of’ truss-box ’ composite truss web continuous beam bridge is well fitted with the finite element calculation value in terms of bending,shear and torsional distortion performance,so the equivalent theory in this thesis has good reliability.At the same time,based on the equivalent theory,this thesis further uses the finite element model to explore the influence of different geometric and load conditions on the normal stress,shear stress and torsional distortion normal stress of composite truss web continuous beam bridge.