Tacoma Narrows Bridge
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Location: Tacoma, Washington, USA
Completion Date: 1940
Cost: $6.4 million
Length: 7,392 feet
Materials: Steel, concrete
Longest Single Span: 2,800 feet
Engineer(s): Leon Moisseiff
On the morning of November 7, 1940, the Tacoma Narrows Bridge twisted violently in 42-mile-per-hour winds and collapsed into the cold waters of the Puget Sound. The disaster -- which luckily took no human lives -- shook the engineering community and forever changed the way bridges were built around the world.
Engineer Leon Moisseiff had designed the ultimate in slender bridges. The roadway was a mere 39 feet -- only eight teenagers lying head to toe would fit across the bridge! Moisseiff strengthened his narrow bridge with a solid steel girder beneath the roadway. But soon after it opened, the Tacoma Narrows started behaving strangely. Wind caused the bridge to sway back and forth, and it also sent rippling waves along the deck. The Tacoma Narrows tore itself apart only four months later.
Years later, engineers found that the solid girders actually blocked the wind and caused the slender bridge to twist. The twisting bridge fanned the steady wind into a swirling motion, which caused the bridge to twist even more -- and eventually snap in two. The Tacoma Narrows Bridge was replaced in 1950 by a new bridge stiffened with a truss. Rather than blocking the wind, the open truss allowed the wind to blow through the new bridge.Here's how this bridge stacks up against some of the longest-spanning bridges in the world. (total length, in feet)