HEADLINE: A bridge to remember
A few months after Galloping Gertie--the Tacoma Narrows Bridge -twisted and undulated itself to destruction in 1940, civil engineering Prof. J. K. Finch, of Columbia University, by-lined an article in ENR titled "Wind Failures of Suspension Bridges or Evolution and Decay of the Stiffening Truss." He recounted numerous instances of aerodynamic instability--some ending in collapse of the structures--dating back to the earliest years of modern suspension bridges.
"These long-forgotten difficulties with early suspension bridges," he wrote, "clearly show that while to modern engineers, the gyrations of the Tacoma bridge constituted something entirely new and strange, they were not new--they had simply been forgotten."
Partly because of Gertie's prolonged and well-photographed demise, forgetting has been harder since 1940. The Triborough Bridge and Tunnel Authority of New York remembers. It is about to spend $2 million to beef up the Bronx-Whitestone Bridge in New York City.
"Widely acclaimed for its slenderness and grace," the Bronx-Whitestone Bridge, like Gertie, was designed and built during a "decay" phase of the stiffening truss. The Whitestone did enough undulating from its earliest days (1939) to attract engineering attention. Some corrective measures were taken during its construction and stiffening trusses were added six years after the Tacoma Narrows Bridge failure.
However, the Whitestone bridge was never a galloper. It was much heavier than the Tacoma bridge for one thing, and weight counts plenty in bridge aerodynamics, according to the experts.
Still, it's reassuring to know that somebody remembers to watch it.