Abstract: Compared with common twotower suspension bridges, the total stiffness of a three-tower suspension bridge is relatively small, and the ratios of the deflection to span of the bridge are larger. The midtower structure of a threetower suspension bridge has great influence on the mechanical behavior of the whole bridge. Based on the analysis of the Taizhou Bridge, a three-tower suspension bridge, the design restrictions of a three-tower suspension bridge were analyzed, such as the deflection of the main span and the anti-slipping safety factor between the main cable and saddle of the midtower. The analysis based on the finite element method shows that the stiffness of the midtower is the key factor of the mid-tower structure selection, the appropriate stiffness of the mid-tower is between 23～28MN／m for the Taizhou Bridge, and the appropriate structure is a herringbone structure.

Key words: three-tower suspension bridge, structure selection of mid-tower, anti-slipping safety factor between the main cable and saddle of the mid-tower