Flutter Response of an Ultra-Large-Scale Full-Bridge Aeroelastic Model of the Old Tacoma Narrows Bridge in Natural Wind

Abstract To investigate the large-amplitude flutter response of the Old Tacoma Narrows Bridge (OTNB), this study employed a 1:8.53 scaled full-bridge aeroelastic model with a main span of 100 m. In natural wind, the aeroelastic model test reproduced the first antisymmetric torsional mode (A-T-1) flutter reported for the OTNB. Numerous flutter events of the aeroelastic model were recorded, including time-histories of girder vibrations, forces of the hangers and main cables, wind speeds, and wind directions.

Three representative flutter cases with distinct flutter responses under different wind conditions were selected for detailed analysis. In Cases 1 and 2, the torsional displacement of the girder shows distinct developing and steady stages, similar to the limit cycle oscillations observed in wind tunnel tests. In Case 3, the torsional displacement amplitude of the girder exhibits alternating growth and decay.

This behavior is seldom observed in conventional wind tunnel tests. In the three cases, the wind speed at the girder height is nearly uniform, and the wind direction remains consistent across the span. The girder’s torsional displacement at the three-quarter span section reaches a maximum of 14°, and the maximum fluctuating forces of the hangers and main cables reach 37.8% and 10.8% of the static equilibrium forces, respectively.

These results demonstrate that the large-scale full-bridge aeroelastic model in natural wind not only reproduces the A-T-1 flutter of the OTNB but also provides new insights into large-amplitude flutter responses under nonstationary wind fields.