| As a new type of cable-supported bridge, cable-stayed suspension has merits of both suspension bridge and cable-stayed bridge, and avoiding the shortcomings of them. Moreover, with the new structure and low costing, it has being more and more attention. With the further research, people have more and more understanding of the static dynamic performance of this type of bridge. However, due to the real bridge of this type built very little, the attempting to this type of bridge still remains in the process of program designing. The most design workers lack of the general certainty and design experience on it, leading to a big obstacle to popularization and application. A very important task for bridge workers now is to create more opportunities in promoting the use of this bridge and let more people think and use this bridge in the design of programs with skilled application. Compared with the other types of advantages and disadvantages, this bridge requires a comprehensive understanding of the structure system which not only from the grasp of its overall force structure properties, but also from the preliminary analysis in some simple and practical way of calculation. The main research work covers the following aspects:(1) This paper has researched the structure system of cable-stayed suspension, and discussed the effects of the ratio of rise to span, ratio of suspension span to main span, and the location of assistant pier on the mechanic behavior of this type of bridge. Comparison between cable-stayed bridge and cable-stayed suspension bridge, and comparison between suspension bridge and cable-stayed suspension bridge have been conducted. Moreover, a comparative study on the mechanical behavior of the earth-anchored and self-anchored cable-stayed bridges was also conducted, and the causes of the differences between the two patterns of bridges are analyzed.(2) Under uniform live load, the formulations of cable/beam live-load ratio for three different types of cable-stayed suspension bridges are deduced, and whose result is verified by that of FEM. Moreover, these formulations are grouped into a united form of formula which could be distinguished by coefficients according to the different boundary conditions and different distribution of the main beam stiffness. Lately the correlation for cable/beam live-load ratio and structure parameters is discussed. It is proved that the cable/beam live-load ratio reflects structure trait and is helpful for holding mechanic characteristic at concept design stage.(3) Based on the Winkler assumption, the united form of transfer matrix suitable for different beams on the elastic foundation is obtained by derivation from basic differential equation for beam. This method takes into account the impact of axial force. Moreover, when the boundary conditions, the main beam stiffness, elastic foundation coefficient are not constants, the method of transfer matrix is still applicable to solve the beam on the elastic foundation. The gravity stiffness the cable-stayed suspension bridge is deduced including the axial stiffness under dead load condition and the vertical stiffness under the action of live load. And the elastic support stiffness of the stay cables to the main beam is also deduced too.(4) The elastic foundation beam method is applied to calculate the internal force and deformation of the main beam of the cable-stayed suspension bridge under live load. And the results are compared by that of FEM through a numerical example. Finally, the strengths and weaknesses of the elastic foundation beam method are summarized to provide guidance recommendations for the application of this practical simplify calculation method in the cable-suspension bridges.
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