Analysis Of Structural Characteristics Of Triple-Tower Twin-Span Suspension Bridge With Tie Cable

In recent years, in order to meet the needs of large-scale engineering construction to cross river or cross sea, multi-span suspension bridge has been proposed and investigated many times. With the new experiences from the design and construction of the first two triple-pylon twin-span suspension bridges, the Taizhou and Maanshan Yangtze River Highway Bridges, the first triple-tower four-span suspension bridge Wuhan Yingwuzhou Yangtze River Bridge, a new upsurge of the construction of multi tower suspension bridge is set off. Multi tower suspension bridge is also one of the most important research areas in the field of bridge engineering. However, the research on its structure characteristics is not perfect as the traditional single span suspension bridge. Especially the research on the middle tower effect, which is the inherent characteristics of multi tower suspension bridge, is still of the practical demand. Deepening understanding of the middle tower effect is also the need for the development of bridge theory.This paper first briefly introduces the development of multi tower suspension bridge and its calculation theory. Aiming at the shortcomings of the mid-tower longitudinal stiffness in triple-tower twin-span suspension bridge, and based on the re-understanding of the middle tower effect of Taizhou Bridge, re-propose the program using the tie cable to connect all of the tower top which is a kind of effective method to improve the overall stiffness of the suspension bridge. This type of bridge is named triple-tower twin-span suspension bridge with tie cable. This paper verifies whether using the cable to improve the overall stiffness of the whole bridge is feasible in technology through theoretical analysis and finite element calculation. This paper extended the common theoretical methods: deflection theory of equivalent beam method, the gravity stiffness method, and structural mechanics successive approximations method to this new type of triple-tower twin-span suspension bridge structure. The corresponding calculation formulas are derived, and the related calculation steps and processesOn the basis of the theory of middle tower effect in Maanshan bridge, the theory of the middle tower effect which is adapted to the triple-tower twin-span suspension bridge with tie cable is put forward. Based on this, the parameters decisive conditions of the key components of the mid-tower and the tie cable are proposed. The FEMs of triple-tower twin-span suspension bridge with tie cable are established based on the Maanshan bridge. Verify the effect of middle tower effect expansion theory, preliminary proved the technical feasibility of cable in the triple-tower twin-span suspension bridge. According to results of the FEMs and MATLAB software based on deflection theory of equivalent beam method, the gravity stiffness method, and structural mechanics successive approximations method, calculation shows that error is in allowance range. The anchoring method of tie cable is proposed through the parameter analysis based on the gravity stiffness method.The FEM is used to analyze the dynamic characteristics of the suspension bridge, including the free vibration characteristic analysis and the nonlinear static wind stability analysis. Analysis of dynamic performance shows that, compared with the conventional triple-tower twin-span suspension bridge, the bridge with tie cable has a larger natural vibration frequency. the elastic-cable system can improve the frequency of drift modes and vertical flexural stiffness, and the wind-resistant performance is optimal among the different reinforced beam support systems. The consolidation system can increase the triple-tower twin-span suspension bridge's natural vibration frequency and torsional stiffness, however decrease the torsional divergence critical wind speed. The buckling mode of the triple-tower twin-span suspension bridge with tie cable is coupled with bending and torsional instability mode. However, when the initial wind attack angle is-3° degree, the gravity stiffness of the suspension bridge increases with the wind speed increases, the structure will not appear static wind instability phenomenon.