Flutter of the Old Tacoma Narrows Bridge model in natural winds: Long-term experiments and statistical analysis

This paper presents a one-year experimental study on large-amplitude flutter responses under natural wind conditions employing a 1:8.53 full-bridge aeroelastic model of the Old Tacoma Narrows Bridge (OTNB). During this period, extensive measurements of wind fields, girder displacements, and cable tensions were conducted under non-stationary wind fields that are challenging to reproduce in conventional wind tunnel tests. A total of 137 flutter events under north wind conditions were selected to statistically analyze the wind field characteristics and structural vibration responses. The estimated flutter critical reduced wind speed ( U cr ) is generally consistent with the values reported in previous studies, which verifies the feasibility of the statistical approach employed. The results demonstrate that, in natural wind fields, both the wind parameters and their spanwise distributions significantly influence the flutter response. Specifically, increases in yaw angle and absolute value of the wind attack angle raise U cr , whereas an increase in longitudinal turbulence intensity reduces U cr . Non-uniform wind fields along the girder span can significantly reduce torsional displacement amplitudes of the girder compared with uniform wind fields of similar average wind speed and yaw angle. Moreover, during the stable stage of the selected flutter events, the maximum increment of fluctuating tension in the hangers relative to the static equilibrium value is approximately 29.5%, while that of the main cables reaches approximately 6.3%. These findings provide valuable insights for wind-resistant design and flutter stability assessment of long-span bridges.