Abstract:The aero-elastic instability mechanism of a tensioned membrane structure is studied in this paper. The response and wind velocities above two closed-type saddle-shaped tensioned membrane structures, with the same shape but different pretension levels, were measured in uniform flow and analyzed. The results indicate that, for most wind directions, several vibration modes are excited and the amplitude and damping ratio of the roof slowly increase with the on-coming flow velocity. However, for particular wind directions, only one vibration mode is excited, and the amplitude and damping ratio of the vibration mode increase slowly with the on-coming flow velocity. The aero-elastic instability is caused by vortex-induced resonance. On exceeding a certain wind speed, the amplitude of the roof vibration increases sharply and the damping ratio of the vibration mode decreases quickly to near zero; the frequency of the vortex above the roof is locked in by the vibration within a certain wind velocity range; the amplitudes of the roof in these wind directions reach 2-4 times the amplitudes for other wind directions. The reduced critical wind speeds for the aero-elastic instability of saddle-shaped membrane structures at the first two modes are around 0.8-1.0.