The Experimental Study And Theoretical Analysis In Shear Lag Effect On Thin-walled Box-girder

Along with the long cantilever plate, the big rib spacing,concise and the single-boxsingle-chamber box bridge, the shear lag effect has been payed attention gradually by people.In recent years, many experts and scholars have devoted themselves to the research of theshear lag effect, and have obtained some achievements. But some problems are still notsolved, especially the shear lag effect of the variable cross-section and curved box girders andit is necessary to research further.Based on the theory of the thin walled bar and the application of the energy functionalvariation principle of the thin-wall box girder, a set of the theoretical calculation methodsuitable for the bending, bending and twisting, bending and the shear lag effect of thethin-walled box girders is established, and it mainly focuses on the theoretical analysis andtest research of the thin-wall box girder shear lag effect and the influence on the bridgebehavior. This paper has six chapters in common. the research theory and method of thethin-walled box girders shear lag are reviewed in the chapter one; Based on the principle ofthe minimum potential energy in chapter two,the shear lag governing differential equation isrespectively established whether the influence of shear deformation is considered or not. Theshear lag formula is given combined with the boundary conditions. The negative shear lageffect and the mechanism of generation are introduced, and the negative shear lag and itsinfluence factors of the cantilever box girder and continuous beam are analyzed in the chapterthree. The control differential equation of the thin wall curved bridge shear lag effect and theanalytical expression under the specific boundary conditions are established by using theenergy variation method in chapter4,5. The mechanical properties and the shear lag effect ofthe curved bridge are analyzed through the model test, and the influence of prestress on theshear lag effect of the curved bridge is studied. The shear lag coefficient of several typicalsingle-box bridge is solved and analyzed by adopting the three kinds of calculation methodsin chapter six, and the distribution regularity of shear lag is studied when the constructionstages of several typical bridge are considered.The following work is mainly completed in thispaper:1. Based on the typical trapezoidal box girders, combined with thin walled bar theory andenergy functional variation principle,the elastic mechanics analysis system of the thin-wallbox girder bending and bending torsional shear lag effect is established and the calculationmethod of thin-wall box girder shear lag is improved.2. According to whether shear deformation is considered, The warping displacement functionswith the shear lag for the thin-walled box girder have been constructed. Furthermore, basedon energy functional variation principle, the governing differential equations for theory ofelasticity in box girders are established on both cases; combining boundary conditions, usingmathematical method gives a closed solution of the governing differential equations; shear lag calculation formula of free beam and continuous beam under concentrated loads and uniformloads has been given; Based on calculation results, discuss on how shear deformationinfluences shear lag effect; and then combining analyzing examples to verifying whetherdeduced theoretical formula is correct.3. Take cantilever girders and continuous girder as examples, to introduce the negative shearlag effect and how the mechanism resulting. confirming the critical point of positive andnegative shear lag effect, analyzing shear deformation, Poisson’s ratio, cross-width ratio,aspect ratio, width-thickness ratio and stiffness ratio other factors on the cantilever beam andcontinuous beam of negative shear lag effect.4. Take the thin-walled curved box girder as an example, according to the theory ofthin-walled curved bar, the shear lag warp displacement functions in fundamental deformationof flange in curved box girders are completed. Considering the effect of the secondary sheardeformation on warp displacement in restraint torsion, the governing differential equations ofthe shear lag effect and boundary conditions are established by the energy variation methodfor thin-walled curved box girders. The energy functional variation principle in shear lag ofstraight box girders is popularized to curved box girders, and the governing differentialequations with consideration of bending, torsion and shear lag coupling are derived, The shearlag effect of two-span single-pillar continuous curve rigid frame bridge are studied by test andlucite model, which has provided helpful experience for design and construction of the similarbridges. The characteristics of shear lag in curved box girder under pre-stress are discussed,compared with the model test, the impact of pre-stress on shear lag of curved box girder areobtained.5. Applied variation method and ANSYS finite element method on several typical single boxsection bridge of shear lag effect for analysis and comparative studies, gaining regular patternof the shear lag effect on behavior of the bridge structure, Based on the above results, somesuggestions on design and construction of box girders are provided, these also have referencevalue on shear lag effect and preliminary design for the same type of bridges.