Numerical and theoretical analysis of spatial shear lag effect in through wide box bowstring arch bridge main girder

Abstract

The shear lag of the box girder section of a wide box bowstring arch bridge was investigated in this study. The finite element analysis software Midas Civil was used to discretize the bridge into separate entities, establish its spatial model, and analyze the law of shear lag effect in the longitudinal direction during the main construction stage and the completion stage separately. The shear lag effect is more prominent at certain key points due to the influence of the tension of the boom and the weight of the arch foot during the construction stage. After the bridge is completed, the axial pressure of the arch foot drives the shear lag effect near the midpoint of the main girder section to its maximum; the axial force is transmitted along the longitudinal bridge direction in a V shape along which it gradually decreases. Under the action of uniformly distributed load, the cross-section of the box girder near the middle fulcrum is affected by the axial force of the arch foot; there is both a positive and negative shear lag effect. Under the eccentric load, the positive and negative shear lag effects appear simultaneously at the end fulcrum. The shear lag coefficient is higher in the web on the eccentric load side than the non-load side. There is obvious and widely fluctuating positive/negative shear lag effect in the vicinity of the middle fulcrum. There is significant tensile stress on the roof under the action of the middle fulcrum. The cross-sectional stress of a single-box seven-cell box girder under compression-bending load action was analyzed according to the finite element analysis results. The stress was decomposed into a superposition of bending moment action and axial force action. The shear lag coefficient λM under the action of bending moment was also solved via energy variation method. Assuming that the axial force is only borne by the compressed area, the shear lag coefficient λN under the action of the axial force was obtained; λM and λN were superimposed to determine the comprehensive shear lag effect coefficient λ.