Experimental Investigation of Effects of Wind Yaw Angles and Turbulence on Postflutter Behaviors of a Suspension Bridge Model

Nonlinear postflutter behaviors of a suspension bridge model with a pi-shaped deck section are investigated, focusing on influences of wind yaw angles and low-intensity turbulence. Structural damping properties are first identified by free decaying vibration in still air. The results show that modal damping ratios increase significantly with motion amplitudes. Wind flows with yaw angles are decomposed into components perpendicular and parallel to the bridge deck axis. The flutter instability under wind yaw angles is examined in terms of the perpendicular component. The experimental results show that while small wind yaw angle (10 degrees and 20 degrees) only slightly improve the critical wind speed U-perpendicular to, the largest wind yaw angle (30 degrees) substantially improves the U-perpendicular to value. Oncoming turbulence of low intensity is found to stabilize the system to some extent, increasing the flutter threshold by about 13% without blurring the demarcation between stability and instability.