Nonliear Analysis And Determination Of Finished State For Spatial Self-anchored Suspension Bridges

With the development of civil engineering technology, self-anchored suspension bridges have been got considerable attention and advanced in recent years. Both at home and abroad, a growing number of self-anchored suspension bridges are in the planning design or construction. Related design theory, analysis and construction technology for this type of bridge still exist many difficulties, which are necessary for further study. This paper emphasized on the theory and method of static nonlinear analysis for spatial self-anchored suspension bridges, Specific studies as follows:(1) The computational method of main cables and suspenders' configurations is studied for space self-anchored suspension bridges according to different structural arrangement. With the recursive- iterative calculation method, the unstrained length, internal forces and spatial location of main cables and suspenders can be solved. Based on the method presented by the paper, a procedure has been coded which is suitable for spatial and planar cable shape finding analysis.(2) Based on the CR formulation, the principles and methods for the geometric of spatial nonlinear analysis frame structures. The math problem of spatial limited rotation is settled through the introduction of Euler-Rodrigues formulation. By defining the global coordinates, element coordinates, nodal section coordinates, rigid displacement and rotation can be accurately deducted, and the at the deformation of the frame's end can be obtained from the computation through these coordinate systems. The accuracy of the results with CR formulation depends on the accuracy of structural unbalanced forces. The unbalanced forces are the differences between the loads and the structural restoring forces. The restoring forces are grouped by each beam's nodal internal forces in the global coordinate system which can be set by the stability function of spatial beam element. Based on the CR formulation, a program for spatial frame analysis is worked out in this paper, which is used Fortran95 language. Some geometric nonlinear examples show that this procedure is accurate and effective which can be used to static nonlinear analysis for spatial bridge structures.(3) Nonlinear effects of self-anchored suspension bridges are studied. The result indicates that, for long suspenders of spatial self-anchored suspension bridges, the large error induced by lateral forces will affect the main cable's spatial location, which should adopt the catenary element. The stiffness matrix of catenary element is derived according to the catenary theory. Nonlinearity caused by initial internal forces should be taken into account when establish updated state balance equation. The effect of stiffening beam's arch is studied for self-anchored suspension bridges. The results show that proper arch is beneficial for the stiffening beam's axial pressure, the moment and deflection by living loads are reduced to some extent. The study for different sag-span ratios shows that stiffening beam's axial pressure is reduced to a rather extend. In the consideration between safety and costs of stiffening girders and main cables, self-anchored suspension bridges should use larger sag-span ratios.(4) The goals and determination method of bridge's finished state are studied. Referring to the methods for determining suspenders' forces in cable-stayed bridges, two methods- uniform mass method and rigid supports continuous beam method are presented for determining the initial suspenders forces of spatial self-anchored suspension bridges. On this basis, the step-by-step analysis procedure is proposed for determining the finished state of bridges.Two examples as symmetric and asymmetric configuration of self-anchored suspension bridges have been analyzed and different suspenders forces layout are studied to prove the method in this paper is effective.