[1]  Screen Shot 2014-02-10 at 11.26.09 PM [2]

Structure: Tacoma Narrows Bridge Collapse
Location: Tacoma, Washington
Year of construction: 1940
Year of failure: November 1940
Type of failure: Aeroelastic flutter
Structural engineer: Leon Moisseiff

The Tacoma Narrows Bridge (also known as “Galloping Gertie”) is a well-known and well-documented suspension bridge failure that occurred on November 7, 1940 at approximately 11am, four months after the bridge was first opened to the public. At first, the bridge’s deck began to experience vertical moment as a result of severe winds. The structure began to violently sway from side to side and eventually began twisting, which was the ultimate failure and caused the bridge to collapse. The bridge was designed in a way that wind would flow above and below the solid sides of the structure rather than through the trusses. Since the wind could not pass through the structure’s solid sides, the bridge ultimately caught the wind and began to sway and twist. The phenomena of the wind and bridge failure is known as aeroelastic flutter. In addition to the twisting torsion caused by the 40mph winds that day, the failure can be contributed to its “excessive flexibility.”

Looking back at the structural design of the bridge, the 8 foot deck was too shallow, side spans too long in relation to the length of the center span, and the cables were too far from the side spans. In addition,  the ratio of the center span length to the width of the deck was an astounding 72:1. The failure of this bridge inspired engineers and physicists to pursue more advanced and in depth research in the field of aeroelasticity and modern suspension bridges. [a]