Static and dynamic properties of three-tower suspension bridge and structural type selection of mid-tower

In order to discuss the static and dynamic properties differences between three-tower and two-tower suspension bridges, and select the rational structure type of mid-tower, based on the Taizhou Yangtze River Bridge, the 3D space finite element models of two-tower suspension bridge and three-tower suspension bridges with concrete mid-tower and steel mid-tower were set up by finite displacement theory and the static and seismal effects were analyzed under various structural parameters. Analysis result shows that compared with two-tower suspension bridge, because the mid-tower is lack of effective restraints from side cables, three-tower suspension bridge has lower total stiffness, lower natural frequency and larger deflection-to-span ratio of main girder. Under vehicle loads, the anti-slipping safety factor between main cable and saddle, the forces of mid-tower and the deflection-to-span ratio of main girder are not important for two-tower suspension bridge, but become controlling indices for three-tower suspension bridge. The indices are related to the anti-pushing rigidity of mid-tower, but have incompatible demands for the rigidity. Under vehicle loads, when the steel mid-tower with upside-down Y shape is selected, the anti-slipping safety factor between main cable and saddle of mid-tower is 2.17, the maximum stress of mid-tower is 182 MPa, the deflection-to-span ratio of main girder is 1/210, and they meet correlative demands. Obviously, due to the application of steel mid-tower, the indices are rationally considered, the stiffness optimization of components and cable system is achieved, so, it is an appropriate structure for mid-tower.