Study On The Stability Of The Cable-stayed Bridge With A "S" Shaped Cable-stayed Pedestrian Bridge

In recent years, with the development of science and technology, for thecable-stayed bridge, not only its span is increasing, but also its tower is higher andhigher. The wider the span is, the larger the axial pressure of bridge tower and mainbeam is. In this case, the structure`s nonlinear effect becomes apparent. Thus, thestructural stability safety factor is greatly reduced, and the stability problems areaccordingly prominent.Two kinds of stability analysis are described in this paper, the first of which revealsits stability is instability of brunch point, and the second of which is essentially theinstability of extreme point. In addition, simplified calculation formula of bridge towerand main beam is clearly derived. To derive the formula, the writer applies generalassumptions and gets the conclusion that the direction of bridge tower instability isinside the cable plane or outside its vertical one. And for the derivation of simplifiedformula about the stability of main beam, the writer applies the energy method andtakes the effect of girder stiffness of the elastic support affected by deformation ofbridge tower into account.In this paper, the engineering background is the NO.1Bridge in Mianyang. Thewriter applies finite element software, MIDAS/Civil, to establish refined models andanalyze the linear elasticity and nonlinear stability during the construction phase andoperation stage of the bridge. The main conclusions are as follows:①In the process of cantilever construction, the instability of the bridge structureis the vertical instability of bridge tower. However, from the side span closure to bridgedeck pavement, the instability of bridge structure is the horizontal instability.②Both the closure of side span and mid span can increase structural constraints.That leads to the change of structural system and strengthening of its integrity. Thus, thestability safety factor can be increased.③The variation trend of the stability safety in the two types of stability analysischanges according to the different construction phases. The most unfavorable phases ofboth situations are the construction phases of cantilever to its maximum size.④When taking the nonlinear effect into consideration, the stability safety factor of bridge structure will be lower. Therefore, in order to get the precise stability of bridgestructure，the nonlinear effect must be considered.⑤The larger proportion of dead load the bridge structure bear, the less influenceof live load to structural stability safety factor will be.