Researches Of Characters And Factors Of Geometrical Nonlinearity Of Large Span Cable-Stayed Bridges

With the quick development of bridges, appearance of new material and great progress in design and construction in recent decades, cable-stayed bridges, by their beautiful shapes and unique structural qualities, have entered into their summit of construction in the world. At the same time the records of spans of cable-stayed bridges have been rewritten again and again, which may catch up with suspension bridges. In the other hand geometric nonlinearity of structures also must be considered in real projects, since their spans become larger and larger, which are near to 1000m.Geometric nonlinear behaviors in large span cable-stayed bridges have been analyzed in this paper, which include the sag of inclined cable stays caused by their own dead weight; the interaction of large bending and axial deformation in bending members; and the large displacements effects. Then analyzing theories and researching levels of geometric nonlinear problems of modern cable-stayed bridges have summarized. And methods of modeling cable-stayed bridges for nonlinear finite element analysis have been discussed, which are the equivalent modulus of elasticity, introducing stability functions and continuously modifying geometry of structure. Then in this thesis some basic methods for geometric nonlinear analysis of cable-stayed bridges have also been discussed and algorithm of co-moving coordinate iteration combined incremental and iterative approach is established. Based on all above theories a computer program named GNACSB is developed and debugged successfully, which can ignore one or all effects of geometric nonlinearitiy. Finally we have studied several examples and discussed characters of geometric nonlinearity of cable-stayed bridges.By fully analysis of two real cable-stayed bridges, following conclusions have been reached: 1) Under dead loads the sag of inclined cable stayed is the main point of geometric nonlinear behaviors of cable-stayed bridges, and the effects of the interaction of large bending and axial deformation in bending members andthe large displacement are relatively small. So it is not enough if we only execute linear analysis to a cable-stayed bridge; 2) When live loads are distributed to full span the effects of geometric nonlinear for the structure are smaller than to two side spans or mid-span only; 3) Linear analysis is enough to live loads since the difference between linear analysis and nonlinear analysis to the structure is relatively small under live loads; 4) The effects of every geometric nonlinear element to decision final shape parameters are very little, and the results of linear and nonlinear are nearly equal; 5)Under construction the effects of geometric nonlinear to cable-stayed bridges must be considered. And only after several iterative procedures we can get ideal initial shape of the structures.