Aerodynamic Interference Effects on Flutter and Vortex-excited Resonance of Bridges with Twin-separate Parallel Box Decks

Abstract:

Taking a preliminary design alterative for the broadening engineering of the existent single-tower cable-stayed bridge, Tanggu Haihe Bridge in Tianjin, with a main span of 310m, the aerodynamic interference effects on flutter and vortex-excited resonance of cable-stayed bridges with twin-separate parallel box decks were investigated via a series of wind tunnel tests of spring-suspended sectional model. The results show that: because of the aerodynamic interference between the two adjacent separate box deck, the flutter critical wind speeds of the twin-separate box deck bridge drops evidently and the turning point of the corresponding aerodynamic derivative curve from descending to ascending is brought forward, compared with those of the existent single-deck bridge. This indicates the decline of bridge flutter stability due to the aerodynamic interference of this type. The results also demonstrated that the maximal amplitudes of the vortex-excited resonance of the of the twin-separate box deck bridge in both the vertical and torsional directions increase due to the aerodynamic interference of this type, compared with those of the existent single-deck bridge. Correspondingly, the lock-in zone of wind speed is widened, and the onset wind speed decreases making the Strouhal numbers increased slightly. It is also found that the aerodynamic interference effect between the two adjacent separate box decks is more significant on the flutter and vortex-excited resonance of the leeward deck than on those of the windward deck. In sum, it is necessary to consider the aerodynamic interference effect when broadening the existent bridge into a twin-separate parallel deck bridge.