Analysis On Mechanical Behavior And Construction Process Of Cable-Stayed-Suspension Bridges

The cable-stayed-suspension bridge is a bridge that suspension cables and stay cables are used together. This bridge type is characterized by relatively new structure, great overall stiffness and long-span capacity. With the promotion of China’s economic and the urgent need for the traffic engineering to cross the rivers or seas, the cable-stayed-suspension bridge has been proposed for the design of some extra long-span bridges. Therefore, it is significant for engineering to take further researches on mechanical properties of this structure. Taking proposed preliminary design of a cable-stayed-suspension bridge with a main span of1800m for engineering background, the mechanical properties, the influence of design parameters on structural static and dynamic characteristics and the closure methods in the construction are studied.Firstly, the development history and structural types of the cable-stayed suspension bridges are briefly reviewed. And the researches that have been done at home and abroad are summarized. Secondly, the software BNLAS for space nonlinear finite element analysis is used to determine the reasonable completed status and study the structural response under different load cases. The main mechanic characteristics could be obtained. Thirdly, in order to study the stiffness of the structure, the three-span suspension bridge and the single-span bridge are analyzed for comparison. Finally, the reasons for the fatigue of the longest suspension cables and the variation of the stiffness at the overlap area are also discussed.By changing the overall layout, the cable-stayed-suspension bridge scheme with different parameter is analyzed. The influence of several parameters (the rise-span ratio, the suspension-to-span ratio, the auxiliary piers, the constraint condition of the girder, the layout of the suspension cables, the height of the girder and the elastic modulus of suspension cables) on structural static and dynamic properties are discussed.Based on the reasonable completed status, the construction model is established by back-running method. The key technical problems in the construction are pointed out. And the closure methods can be adopted are also studied.The study indicates that the cable-stayed-suspension has the merits of reasonable structure, great overall stiffness and better wind-resistant performance. Because the distance of the non-cables area near the pylon is longer, the vertical stiffness of main cables is relative small. However, the stiffness increases suddenly at the place of the longest suspension cables, which leads to the variation quantity of the cable force increases. The difference of the vertical stiffness between the cable-stayed area and suspension area leads to the variation of the stiffness at the overlap area. From the viewpoint that reduces the internal force amplitude of the longest suspension cable under live load, the lager suspension-to-span ratio and the wire ropes for suspension cables should be adopted. And setting up an overlap area is also helpful. From the improvement of the stiffness transition between the cable-stayed area and suspension area, it is reasonable to set up an overlap area. From the consideration that increases the overall stiffness, the auxiliary piers should be installed at side spans and the suspension-to-span ratio should be approximately equal to0.5. In the construction, the construction plan that the cable-stayed area and suspension area are erected at the same time is feasible. The closure mearsures such as stay cables tensioning, loading or combination of temporary suspension cables tensioning and loading could be adopted.Through the analysis of the mechanic behavior and construction process above, the conclusions may be of some value for the design and further study of the cable-stayed suspension bridges in future.