Aerodynamics of the Tacoma Narrows Bridge - 60 Years Later

This article takes a new approach to understanding the aerodynamics failure mechanism responsible for the collapse of the Tacoma Narrows Bridge 60 years ago. It is demonstrated that the instability mechanism is associated with the formation and drift of large vortices from the upwind edge of the bridge girder cross section. An empirical model of the vortex formation and drift process is formulated that allows critical wind speed for onset of the instability to be estimated. The model is supported by numerical simulations and experimental results. It is shown that a structural modification of the Tacoma Narrows Bridge cross section would have suppressed the vortex formation or counteracted the aerodynamic actions and thus rendered the bridge more aerodynamically stable.