Optimization Research And Application On Steel-box Girder Of Self-anchored Suspension Bridge

Jianshe Bridge is a self-anchored suspension bridge on Qingshui River in Zhangjiakou City.According to the operating and geological conditions,flat side main steel-box girder was used instead of traditional flat single-box girder.As the large width-thickness ratio,the structure and force of side main steel-box girder were very complicated.In this paper,static analysis,local buckling analysis of steel-box girder project and lateral calculation of diaphragm plate were completed.The main contents of this paper were as follows:(1) Thought consulted the domestic and foreign related professional literature and data,the development,structure and characteristics of self-anchored suspension bridge were elaborated in detail,meanwhile,many kinds of calculation theories and analysis method of self-anchored suspension bridge and orthotropic steel-box girder were studied.(2) By means of compared with static models of flat side main steel-box girder and traditional flat single-box girder with various girder height,many important properties were found.Such as,the flat side main steel-box girder was superior to traditional flat single-box girder with the same cross-section size in the economy and construction.In the force of girder, the stress of flat side main steel-box girder satisfies the allowable stress of steel,and the stress of traditional flat single-box girder was so small that conservative design and materials waste will occur.(3) Based on analyzing to the local buckling model of flat side main steel-box girder,the bridge deck system composed of roof plate,longitudinal rib and diaphragm plate played the most important role.The thickness variation of bottom plate,web plate and web stiffener has a definite effect on local stability of steel-box girder,because the area ratio of them is limited in the girder.The local stability of girder could be enhanced by constrained deformation of diaphragm plate,simultaneously,the aspects of force and stability for cross section of steel-box girder needed further research.(4) The model results using mixed finite element and traditional finite element for diaphragm plate respectively showed that a maximum value of diaphragm plate normal stress appeared in the middle of main span and the minimum value in the middle of side span,the values of shear stress had little difference in both models.The difference of diaphragm plate stress is small in the middle and quarter of main span,so the diaphragm plate model in main span will be used for typical calculation.Respectively corresponded to points on the girder,the ratio of diaphragm plate stress of both finite element models equals to about 0.5 that shows a certain regularity and relevance of two calculating methods.Due to considering the force characteristics of individual diaphragm plate,finite action of roof and bottom plate,no restraint effect of U-rib,web plate and other stiffener,impact of higher vehicle load value,the stress results within the allowable limits of steel,the traditional finite element method for diaphragm plate could still be used for Jianshe bridge,though it was a conservative method with the simple model.