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C674
Othmar Ammann and the Great Gray Bridge

Jeffrey Syken

It was the most important bridge of the 20th Century, not because it ended the island of Manhattan’s isolation from the rest of the continent forever (it did just that) but, rather, because it would enable all the “unbridgeable” water gaps – from San Francisco Bay, to the Mackinac Straits and even the Inland Sea of Japan – to be bridged by a long-span suspension bridge in its aftermath. First formulated in Austria by reinforced concrete expert Joseph Melan, “Deflection Theory” was introduced to America by a Latvian immigrant named Leon Moisieff. A brilliant mathematician, Moisieff extrapolated the theory’s principles into a series of mathematical formulas that could be applied to the design of long-span bridges – just like the one needed to bridge the Hudson River between Fort Washington (NY) and Fort Lee (NJ).

In the slender design of the Manhattan Bridge (1909), Moisieff first applied Deflection Theory to a suspension bridge’s supersturcture, saving hundreds of tons of steel that would have been otherwise necessary using traditional design methods (with significant cost savings the bonus). For the 3,500-foot main span required of a Hudson River bridge, a stiffening system eleven stories high weighing from thirteen to fourteen thousand pounds per foot would have been required using traditional methods. Designer Othmar Ammann gambled, applying Moisieff’s formulations to a bridge more than double the main span of any bridge then in existence. Fortune favors the bold and Ammann’s bold gamble paid off handsomely. The sleek upper deck of the first phase of construction (the lower deck would be added in 1962) weighed only 1,100 pounds per foot while the bridge itself was completed well ahead of schedule and a million dollars below budget. The engineering world took notice and was suitably impressed, not only by the bridge itself but also by Ammann; the brilliant, modest “man of genius.”

The George Washington Bridge was not only an edifice of great functional beauty, but completely stable under the tremendous traffic loads it carried with ease and absent of movement, even in the strongest wind. Deflection Theory was proven beyond doubt, allowing bridges like the Golden Gate (1937), Mackinac Bridge (1957) and the longest suspension span of them all – the Akashi-Kaikyo Bridge (1998), to be successfully designed and built. The challenge of spanning the mighty Hudson - long dreamed of - had been achieved with the opening of the bridge in October 1931. It would be the first in a series of bridges and tunnels in the New York City area designed (or supervised) by O.H. Ammann - the legendary engineer of Swiss origin. The culmination of his brilliant career and last hurrah, as it turned out (he died in 1965), would be the Verrazano-Narrows Bridge (1964). However, his first triumph - the George Washington Bridge, launched Ammann on his famed career as a bridge engineer. For his mentor and friend Gustav Lindenthal, it represented a betrayal of trust and the disappointment of a lifetime.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.


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