| As modern bridges become more long-spanned and flexible, the wind-resistance performance has become a major concern in the design and construction of a long-span bridge. In this work, wind tunnel tests of two typical bridge deck sectional models are carried out to study the characteristics of the soft flutter oscillations. The work done by the wind flow is studied. The characteristics of the self-excited force are analyzed in the time and frequency domains. Some main results are summarized as follows:(1) For the wind speed region after the critical flutter wind speed, the sectional models always perform limit cycle oscillations. The steady-state amplitudes of the soft flutter oscillations increase with the wind speed. As the wind speed increases, the phase differences between vertical bending and torsional vibration tend towards opposed phase. For the steady-state oscillation at a certain wind speed, the offset of torsion center changes periodically with a frequency of 2f(fis the fundamental vibration frequency of the deck). The variation tendencies of the torsion center offsets of the bluff deck and the streamlined deck are quite different.(2) During the soft flutter oscillation, the oscillation amplitude has little influence on the surface pressure coefficient distributions. However, the degree of flow separation increases with the increase of the amplitude. For the two models at positive angles of incident, the oscillations of the models are governed by the measuring points on the deck surface. Therefore, the soft flutter oscillations are more likely to occur at positive angles of incident. For zero and negative angles of incident, the railings significantly disturb the flow around the model.(3) The self-excited forces contain significant high-order harmonic components. For the bluff deck, the high-order harmonic components are more significant in the self-excited moment for the bluff deck, while more significant in the self-excited lift force for the streamlined deck. In the regions with obvious flow separation, the ratio of the fundamental component is relatively higher. The high-order components are mostly distributed in the regions of flow reattachment. Therefore, it could be concluded that the reattachment of the separated flow is the major reason for the generation of high-order components. |
