Influence analysis of the incremental launching of steel box girder and local stability control

Incremental launching method is generally used for steel box girders of long-span self anchored suspension bridge during construction. First, the mechanical characteristics of the pushing process and the three bending moment equations were introduced. Second, in Guihua Bridge, design parameters influence analysis of the incremental launching process of steel box girder was carried out. The results of the analysis showed that the maximal displacement at the front of guide beam, the bending moment at steel guide beam root, and the maximum tensile stress of steel box girder as well as the compressive stress of steel box girder periodically change along with the construction process. Meanwhile, elastic modulus and Poisson's ratio have a little influence on the stress and deformation of the steel box girder during incremental launching process. The length of the steel guide beam and its average line weight density have an important influence on the stress and deformation of the steel box girder during incremental launching process. Finally, on the basis of the elastic thin plate theory of small deflection, local stability analysis of steel box girders during the process of incremental launching was carried out. Theoretical calculation showed that the local stability of the steel box girder does not meet the requirements before stiffening, but after stiffening, the local stability fulfills the requirements. By considering the constraint factors of plate groups, material nonlinearity, initial geometric imperfection as well as residual stress, finite-element analysis showed that the stress by self-weight has a little influence on critical buckling stress, which can be neglected. Installing a diaphragm plate to improve the effect of local buckling of the steel box girder is obvious. The analysis results show that the stress of local buckling for the steel box girder is less than the structural maximum working stress during the process, and the risk of instability would be presented.