Study On Mechanical Properties Of Composite Girders With Corrugated Steel Webs

Composite girder with corrugated steel webs(CSWs)is a novel thin-walled steel-concrete composite structure.It has a unique accordion effect,excellent structural characteristics,and significant economic benefits.It gives full play to the mechanical advantages of two typical materials and overcomes the problems of self-heavy weight,long-term creep and deflection of traditional concrete bridges in current bridge engineering,and realize rapid weight reduction of the bridge.It is one of the typical structures of high specific strength and lightweight web composite girders,and has been widely used in bridge engineering at home and abroad.With the continuous improvement of the construction level of the project,the development of composite bridges with CSWs presents new features such as large spans,large curvatures,wide cantilevers,variable sections and new construction methods.By considering these new characteristics,this paper focuses on the buckling performance,transverse force and shear state of this new type of composite girders,and conducts a systematic study on the key issues.First of all,due to the difference between the stress characteristics of composite girder structures with CSWs under the initial curvature effect and that without the curvature,the traditional calculation theory is no longer applicable to the initial curvature situation.In this paper,the theoretical study of shear buckling of composite girders with CSWs with initial curvature was carried out.Secondly,considering the effects of initial curvature,web stiffness and top slab stiffeners,the transverse performance of composite girders with CSWs was studied;Finally,the shear theory of the composite box girder with CSWs in the large-cantilever asynchronous pouring construction stage is proposed and the shear resistance role of lined concrete is revealed.The main research work is as follows:(1)Based on the classic theory of plate and shell,and combines the constitutive relationship of CSWs equivalent as orthotropic shells,the geometrical equations considering initial curvature and equilibrium differential equations,the global shear buckling control differential equations of CSWs in curved girders are derived and iterated.Because CSWs are generally long narrow along the longitudinal bridge,here based on the deflection surface function of long narrow shells,the method of calculating extreme value by variational method and symbolic calculation by using mathematical software,the formula for calculating the overall shear buckling stress of CSWs in curved girders is proposed.In order to reveal the mathematical principle of the formation of the new web's initial curvature,based on the triangular relationship between each panel segment of the CSW and the radius of curvature,the internal relationship between the inside and outside folded angles and the radius of curvature was clarified,the relationship among the inside,outside folded angles and the intersection angle about the central axis is clarified,and the parameterized analysis method is used to study the change law of the key parameters(the web's overall dimensions,height-thickness ratio,panel aspect ratio,corrugation height,radius of curvature,internal and external folded angles)affecting the global shear buckling stress of the CSW with constant curvature or variable curvature were studied,thereby the pure shear buckling problem of CSW composite girders with initial curvature was solved.(2)Based on Timoshenko theory,this paper studies the change law of local shear buckling of CSWs in curved girders under the influence of different parameters with varied width ratio of the panel segments,determines the distribution range of the local buckling coefficients and gives their average value.Based on the synthesis theory of Lindner and El-Metwally,the interactive buckling formulas with different panel aspect ratio ranges are given,the two-stage unequal synthetic index and the design formula of the shear buckling of the CSW in curved girder are proposed,discriminant formulas for different buckling modes are provided,which effectively separate the different buckling modes of the previous experimental results of CSWs,and the rationality of the design curve is confirmed in this paper,thereby the engineering design of the CSWs in composite girders considering the initial curvature effect could be guided.(3)Considering the influence of the initial curvature,this paper analyzes the change law of transverse bending moment and effective distribution width of the composite girder bridge deck with CSWs under concentrated load at different positions,points out the inapplicability of the transverse bending moment coefficient in the existing bridge specifications,gives a new correction formula,and finds two unfavorable working conditions.Therefore,it is suggested that attention should be paid in engineering practice.(4)Based on the gradual evolution relationship of the three typical girders of traditional concrete girders,composite girders with flat steel webs and composite girders with CSWs,equivalent analysis models are established among the three through the web's equivalent stiffness method.By considering the influence of the web's transverse stiffness,the differences in the degree of restraint of the different webs on the bridge deck were reflected,the effects of different web stiffnesses on the transverse stress of bridge deck under self-weight or vehicle loading were quantitatively studied.In addition to studying the influence of the main corrugation sizes(corrugation height,web thickness,and panel length)and elastic modulus on the girder's transverse stiffness,new key factors(web height and cantilever slab width)affecting the transverse performance of the girder with wide bridge deck have also been introduced,and an effective distribution width correction factor is proposed to confirm the accuracy of the model.(5)Based on the traditional concrete girder construction method and the evolution relationship of composite girders with different bridge deck forms,this paper establishes the structural form of the CSW composite girder with ribbed slab.A comparative study and parametric analysis of the influence of key geometric parameters(rib width,height,and spacing)on the transverse stress at the cantilever slab root of a ribbed slab composite girder with CSWs was carried out.It is pointed out that the transverse stress distribution state under dead weight has a wave effect and is significantly different from that under wheel force,which reveals the effective reduction effect of ribs on transverse stress,and a reasonable range of values for the rib key design parameters could be given,thereby the design of the cross-section and reasonable structural dimension design of composite girder bridge deck with CSWs could be guided.(6)Based on large cantilever asynchronous construction models with CSWs,the parabolic function expressions of the girder height and the bottom slab thickness and the equivalent relationship of the construction load were determined,different mechanical areas of the girder body were divided,and the shear stress distributions in the stable and unsteady areas were clarified.Combined with the two-stage construction mode of asynchronous casting,the bearing state of unlined and lined concrete web girders with CSWs have been studied.Finally,the shear theory of large cantilever asynchronous pouring of CSW composite girders with parabolic variable section under multiple concentrated forces was proposed,and the accuracy of the numerical models was confirmed accordingly,thereby the problem of the shear bearing capacity of the large cantilever asynchronous pouring construction state of the composite bridge with CSWs was solved,the adverse situation in the construction stage could be avoided,and reasonable suggestions could also be provided for the design stage.Additionally,this paper elaborates on the novel asynchronous pouring construction method,which innovatively uses the CSW itself as the load-bearing structure in the construction stage,realizes the simple support of the hanging basket system and the expansion of the working platform,greatly saves construction time and reduces the weight of the hanging basket,enables rapid construction,and promotes the industrialization of bridges.