Aerodynamic optimization for flutter performance of steel truss stiffening girder at large angles of attack

The flutter performance of a suspension bridge with truss girder, spanning deep canyon in the dry-hot river valley area where strong wind shows large angle of attack, is analyzed by wind tunnel test. The effects of different horizontal and vertical aerodynamic countermeasures are compared to find effective optimization schemes for improvement of the bridge flutter stability, and a simplified CFD model is further presented to study the corresponding aerodynamic mechanism from the work done by aerodynamic forces perspective. The results show that the combination of central closed deck and vertical stabilizers is favorable to the flutter performance of the suspension bridge. At lower angles of attack, a pair of vortices formed behind the upper and lower stabilizers alternately during the torsional vibration, acts on the downstream bridge deck and produces negative energy which makes the flutter frequency decrease and the critical wind speed increase. On the other hand, at larger angles of attack, the existence of lower stabilizer hinders the movement of the vortex on the same side which becomes the main factor for the occurrence of torsional flutter, and reduces the input energy by aerodynamic forces, which makes the critical wind speed increase with the same flutter frequency.