Effects of types of bridge decks on competitive relationships between aerostatic and flutter stability for a super long cable-stayed bridge

Aerodynamic configurations of bridge decks have significant effects on the aerostatic torsional divergence and flutter for super long-span bridges, which are onset for selection of suitable bridge decks for those bridges. Based on a cable-stayed bridge with double main spans of 1500 m, considering typical twin box, stiffening truss and closed-box section, which are the most commonly used form of bridge clerks and assumed that the rigidity of those section is completely equivalent, are utilized to investigate the effects of aerodynamic configurations of bridge decks on aerodynamic instability performance comprised of the aerostatic torsional divergence and flutter, by means of wind tunnel tests and numerical calculations, including three-dimensional (3D) multimode flutter analysis and nonlinear aerostatic analysis. Regarding the aerostatic torsional divergence, the results obtained in this study show twin-box section is the best, closed-box section the second-best, and the stiffening truss section the worst. Regarding the flutter, the flutter stability of the twin-box section is far better than that of the stiffening truss and closed-box section. Furthermore, wind-resistance design depends on the torsional divergence for the twin-box and stiffening truss section. However, there are obvious competitive relationships between the aerostatic torsional divergence and flutter for the closed-box section. Flutter occur before aerostatic instability at initial attack angle of +3 degrees and 0 degrees, while the aerostatic torsional divergence occur before flutter at initial attack angle of -3 degrees. The twin-box section is the best in terms of both aerostatic and flutter stability among those bridge decks. Then mechanisms of aerostatic torsional divergence are revealed by tracking the cable forces synchronous with deformation of the bridge decks in the instability process. It was also found that the onset wind velocities of these bridge clerks are very similar at attack angle of -3 degrees. This indicates that a stable triangular structure made up of the cable planes, the tower, and the bridge clerk greatly improves the aerostatic stability of the structure, while the aerodynamic effects associated with the aerodynamic configurations of the bridge decks have little effects on the aerostatic stability at initial attack angle of -3 degrees. In addition, instability patterns of the bridge depend on both the initial attack angles and aerodynamic configurations of the bridge clerks. This study is helpful in determining bridge decks for super long-span bridges in future.