Research On Mechanical Behavior Of Cantilever Structure In A Widened Concrete Box Girder Bridge

In the expressway expansion project,the interaction between the old and new box girder after widening and the stress state of the existing box girder in the prestressed concrete continuous box girder bridge are urgently needed to be concerned.The interaction between the old and new box girder will have an irreversible effect on the stress state of the existing box girder structure,both favorable and unfavorable factors.In this paper,the finite element method is used to study the interaction between the old and the new box girder and the stress state of the existing box girder.The research results can provide the reference value for the transverse widening design of the prestressed concrete box girder bridge.Based on the Yan Shao River Bridge widening project of Huaijiang expressway,the transverse force state of the widened structure is systematically analyzed in this paper,especially the splicing site.A simplified calculation method of elastic support frame is proposed for the calculation of the transverse force of the box girder.This paper analyzes the structure with the help of computer software.The finite element model of full-bridge structure is established by Midas FEA,and the transverse stress and distribution characteristics of the bridge before and after widening are studied.The load conditions considered in the analysis include the difference of shrinkage and creep of the new and old box girder,foundation settlement difference,the live load and the temperature gradient.The structural model of grillage method and the model of elastic support frame method are established by Midas Civil.The grillage method model is used to analyze the elastic support stiffness.And the feasibility and accuracy of the elastic support frame method for analyzing the structure are studied.The results show that the stress concentration phenomenon occurs in the joints between the old and new girder under the dead load.The transverse stress produced by the foundation settlement difference is mainly located in the wet joint and both sides of the flange.The maximum stress under the load of the lane load is generally found in the old and new bridge splice joints and the roof and floor of the old bridge.Under the effect of gradient temperature,there will be a large increase in transversal stress in the inner flange of the old bridge.The elastic support frame method can provide a reference for the bridge widening design as a simplified calculation method in the preliminary design.