Tacoma Narrows 50 years later—wind engineering investigations for parallel bridges

Wind engineering investigation of the Parallel Tacoma Bridges was performed. Half a century after the historic collapse of the original Tacoma Narrows Bridge, aerodynamic instability was again the principal concern. Since it was proposed to build a new parallel bridge only 61 m from the existing bridge, aerodynamic interference effects between the two structures were carefully examined. Initially the local wind climate and the bridges' wind exposure were examined. Sectional models and full aeroelastic models of both bridges were constructed and tested to evaluate aerodynamic stability and wind loading. In addition, full-scale measurements were undertaken on the existing Tacoma Bridge for identification of the natural frequencies of the lowest lateral, vertical, and torsional modes. The study program established that both bridges would be aerodynamically stable and provided detailed wind load distributions for structural design.