Study On The Wind Stability Of Super Long-span Partially Ground-anchored Cable-stayed Bridges

To meet with the requirement of China’s road transportation construction in the 21 st century, the span of cable-stayed bridges is increasing gradually, especially the building of Sutong Yangtze River Bridge, the construction of cable-stayed bridges with main span beyond1000 meters has entered into a new era. As the span record of cable-stayed bridges has been refreshing constantly, structural stiffness of cable-stayed bridge has declined greatly. As a result, the wind stability has become one of the main problems which plays a key role in the design and construction of long-span cable-stayed bridges. To explore favorable structural system of cable-stayed bridge with ultra kilometer span, this thesis mainly focuses on a super long-span partially ground-anchored cable-stayed bridge whose main span is 1400 km, and the dynamic characteristics, the aerostatic stability and aerodynamic stability of the ridge are comprehensively investigated. The feasibility of using the design concept of partially ground-anchored cable-stayed bridge in super cable-stayed bridges with ultra-kilometer span and its favorable structural systems are discussed from the aspect of wind stability. The results provide good guidance for the wind-resistant design of ultra-kilometer cable-stayed bridges.Firstly, Midas/Civil software and the computer program of three-dimensional nonlinear wind stability analysis of long-span bridgesare used to analyze the dynamic characteristics, the aerostatic and aerodynamic stability of a partially ground-anchored cable-stayed bridge with 1400 m main span. Through comparison with those of a self-anchored cable-stayed bridge and a suspension bridge(Jiangyin Bridge) with the same main span length, the partially ground-anchored cable-stayed bridge has been proved to be more advantageous in the aspect of dynamic characteristics, aerostatic and aerodynamic stability. Secondly, the effects of main design parameters of partially ground-anchored cable-stayed bridge including the length of ground-anchored segment, the number of auxiliary piers in side spans, the height and width of girder, the height-span ratio of towers etc on the dynamic characteristics, aerostatic and aerodynamic stability of a partially ground-anchored cable-stayed bridge bridge are analyzed, and the key design parameters and also their reasonable values are proposed. Finally, the wind stability of super long-span cable-stayed bridge under construction is investigated.The results show that: 1) as partial stay cables in side spans are ground-anchored, structural stiffness of cable-stayed bridge enhances,structural natural frequency increases, and the aerostatic and aerodynamic stability thus increase. In terms of wind stability, the partially ground-anchored cable-stayed bridge is more favorable to cable-stayed bridges with ultra-kilometer main span. 2) the partially ground-anchored cable-stayed bridge can gain good aerostatic and aerodynamic stability incase of increasing the ground-anchored segment length, increasing the height and width of girder, setting several auxiliary piers in side spans and increasing the height-span ratio of the bridge towers. 3) With the evolution of girder erection, the vertical bending frequency varies slightly, but the lateral bending and torsional frequencies decrease remarkably, and the modal coupling between the lateral and torsion modes enhances, and the wind stability decreases greatly. On the whole, the critical wind speed of structural instability is so high that it has good wind stability for the cable-stayed bridges with ultra-kilometer span under construction.