Study On Dynamic Characteristics And Wind Stability Of Three-Tower Suspension Bridges

Compared with the common two-tower suspension bridges with single mainspan, main spans of three-tower suspension bridges can be greatly shortened, and the cables' tensional forces, the size of anchorages and also the cost are thus decreased significantly, so it becomes a competitive solution for long and particularly super long span bridges. However due to the lack of effective longitudinal restraint for the center tower, structural stiffness becomes lower than that of the two-tower suspension bridge, and therefore the three-tower suspension bridge becomes more susceptible to the wind action. Therefore, comprehensive investigation on the wind stability of three-tower suspension bridges has important theoretical values and great significance for engineering practice.Firstly, by taking a three-tower suspension bridge-Taizhou Highway Bridge over the Yangtze River with main spans of 1 080 m as example, structural dynamic characteristics, the aerostatic and aerodynamic stability are investigated numerically by the finite element based dynamic characteristics analysis, 3D nonlinear aerostatic and aerodynamic analysis. Through the comparison with the results of the section-model wind tunnel test, the validity of the analytical methods used in this paper is thus verified.Secondly, based on the example bridge, case bridges are designed to investigate the effect of structural parameters on the wind stability, such as the cable's sag to span ratio, the side to main span ratio, the girder's dead load, the girder's bearing system and the center tower's longitudinal stiffness etc. Structural dynamic characteristics, the aerostatic and aerodynamic stability are investigated numerically, and considering the aspect of wind stability, the rational values of these parameters are also discussed.Finally, to investigate the effects of structural style of the center tower and the cable system on the wind stability, case bridges with two structural styles of the center tower(A-shaped and inverted-Y shaped in side view) and two cable systems(the spatial cable system and double cable system) are designed. Through the analysis, structural system of three-tower suspension bridges with good wind stability is discussed.The results show that good aerodynamic stability can be obtained for three-tower suspension bridges as the cable's sag to span ratio is assumed ranging from 1/10 to 1/11, the central buckle are provided between main cables and the girder at midpoint of main spans, the A-shaped center tower or the inversed Y-shaped center tower is used, and the spatial cable system or double cable system is employed.