To engineers Gertie's "bounce" represented "structural instability." They set about trying to fix the "vertical oscillation."
From the first week of May 1940, as workmen finished the bridge's floor system, engineers and others noticed the deck's vertical wave motions, or "bounce." They knew something was wrong. Months before, in the summer of 1939, they had heard rumors of similar small waves in another suspension span, the Bronx-Whitestone Bridge, which opened in April 1939. The Bronx-Whitestone Bridge, like the Tacoma Narrows Bridge, had been designed by consultant Leon Moisseiff of New York.
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