Improvement of Flutter Performance of a Streamlined Box Girder by Using an Upper Central Stabilizer

Streamlined box girders are widely used when designing long-span bridges owing to their aerodynamic and aerostatic stability. However, the flutter performance of this type of girder requires improvement when they are employed in extreme wind load conditions. Based on wind tunnel tests and coupled flutter analysis, in this study, we attempted to improve the flutter performance of streamlined box girders by configuring them with an upper central stabilizer (UCS), which was then applied to a long-span suspension bridge being constructed in southern China with a main span of 1,666 m connecting Shenzhen and Zhongshan. Initially, aerostatic wind tunnel tests and free vibration tests were conducted in a wind tunnel. The results show that the girder configured with the UCS could have higher drag coefficients and could also reach a higher critical flutter speed than the ones without UCS, indicating that a higher UCS is not suitable for aerostatics, but the girder's flutter performance was aerodynamically enhanced. Then, to investigate the dynamic mechanism behind this enhancement, flutter derivatives of the girder with UCS were extracted from forced vibration wind tunnel tests and used in flutter analysis. The calculated results agreed well with the test results. Finally, a series of parametric tests were conducted to analyze the dynamic mechanism of enhancement, including evaluation of the aerodynamic damping ratio, phase lag, amplitude ratio of vertical to torsional motion, and energy participation levels of the two types of motion. The analytical results revealed that the enhanced flutter performance of the box girders can be mainly attributed to an increase in the uncoupled aerodynamic damping ratio which is directly related to the flutter derivative, and changes in the phase lag, amplitude ratio, and energy participation level can be described as a unified result of the variation in the UCS height.