Keeping the nose to the wind: key to aerodynamic stability of suspension bridges*

For the past three decades significant amount of research has been conducted on aerodynamic stability of bridge girders. Current wind tunnel measurements and numerical fluid-structure-interaction computational fluid dynamics (FSI-CFD) simulations have revealed that a twin-box bridge deck obtains a higher aerodynamic stability when the bridge deck assumes a "nose-up" twist relative to horizontal when exposed to high wind speeds. From the investigations it is found that a moment coefficient having a positive value at 0° of rotation angle and a positive slope, decreasing with increasing mean angle of rotation, leads to a decrease in the reduction of aerodynamic stiffness through the Α^*₃ coefficient. This in turn ensures an increase in aerodynamic stability. Thus, a positive moment coefficient at 0° with a positive slope, decreasing with increasing mean angels of rotation, is desirable for achieving higher critical wind speeds for onset of flutter than predicted for the deck cross section being horizontal. Through this study, a flutter model is developed for a twin-box bridge deck which allows prediction of the increase of the critical wind speed for onset of flutter as function of the deck section rotation angle.