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Authors: David McCullough

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BOOK: The Great Bridge
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A wire suspension bridge was built over the Schuylkill at Philadelphia as early as 1816, or fifteen years after the Reverend James Finley put his historic little chain bridge over Jacobs Creek. But it was the brilliant Scottish engineer Thomas Telford who completed the world’s first great suspension bridge nine years later, in 1825, in Wales. It had two massive masonry towers and was hung on immense iron chains and it crossed the Menai Strait to the island of Anglesey, with a main span of nearly six hundred feet. It was the most famous bridge of its day and the prototype of all the great suspension bridges to came after it, including those by John A. Roebling.

Isambard Kingdom Brunel, the improbable little genius who would one day build the
Great Eastern,
the most colossal iron ship in history, also began building suspension bridges about this same time, as did the Swiss, the Germans, and the French. The Grand Pont, a suspension bridge built at Fribourg, Switzerland, in the 1830’s, was not only very large for its time (more than eight hundred feet), but it would stand for a hundred years.

But in 1845, when a proposal was made to use a suspension bridge to carry a railroad over the Niagara Gorge, most of the experts declared the scheme quite impossible. Vibrations set up by so heavy a moving load as a train would, it was said, quickly destroy any wire-hung bridge. Still, the idea of a railroad crossing at Niagara made a great deal of sense to the American and Canadian railroad people and they were encouraged by four engineers who not only thought the thing could be done but were anxious for the chance to do it. Of the four, interestingly, three would eventually span the gorge with bridges of their own design—Serrell, Roebling, and Keefer. But as fate would have it, none of them got the first chance.

The man who did was Charles Ellet, who in 1845 was the best-known bridgebuilder in America. He was also the most flamboyant, the most interesting, and Roebling’s one serious rival. Except for Roebling, he knew the most about suspension bridges and could turn on more fancy talk about them than anyone in the profession. Of all the American engineers of his time, Charles Ellet was the most impetuous and colorful, a genuine character of the sort who came and went with the nineteenth century.

Born in 1810, which made him four years younger than Roebling, Ellet had grown up in Pennsylvania, the son of a Quaker farmer. At seventeen he left home, worked on various canal jobs near home, taught himself French, and saved enough money to go to Paris to study at the Ecole Polytechnique. When he returned home after a year, he was the first native American with a European education in engineering. Almost immediately, he presented Congress with a plan for a thousand-foot suspension bridge over the Potomac at Washington and talked grandly of another over the Mississippi at St. Louis. Then he actually built one over the Schuylkill near Philadelphia in 1842, which was several years before Roebling had built anything. (Roebling had applied to build the same bridge himself, and when Ellet was chosen, Roebling wrote to commend him for so bold a plan. Thinking Ellet an older, more experienced man, Roebling applied for a job as his assistant. Ellet’s reply was quite formal and vague, so Roebling wrote again, this time generously including drawings and notes on his own ideas; but nothing more ever came of it.) Five years after that Ellet had begun his greatest work, over the Ohio River at Wheeling, the first really long suspension bridge on earth. With a center span of 1,010 feet, it was only forty-seven feet shorter than Roebling’s own bridge over the Ohio would be and Roebling’s bridge would not be completed for another twenty years.

Ellet looked like an actor, with dark, brooding eyes and a lithe, athletic build. And all of his other talents aside, nobody made a better show of bridgebuilding. At Niagara he had a stage magnificently suited for the most thrilling performance of his career, and the last one, as it happens.

One of the first problems to be faced at Niagara was how to get a wire over the gorge and its violent river. Ellet solved that nicely by offering five dollars to the first American boy to fly a kite over to the Canadian side. The prize was won by young Homer Walsh, who would tell the story for the rest of his days. Once the kite string was across, a succession of heavier cords and ropes was pulled over, and in a short time the first length of wire went on its way. After that, when the initial cable had been completed, Ellet decided to demonstrate his faith in it in a fashion people would not forget. He had an iron basket made up big enough to hold him and attached it to the cable with pulleys. Then stepping inside, on a morning in March 1848, he pulled himself over the gorge and back again, all in no more than fifteen minutes’ time, and to the great excitement of crowds gathered along both rims.

“The wind was high and the weather cold,” he wrote, “but yet the trip was a very interesting one to me—perched up as I was two hundred and forty feet above the Rapids, and viewing from the center of the river one of the sublimest prospects which nature had prepared on this globe of ours.”

Ellet appreciated the historic significance of his feat—he was the first man to cross the gorge—but he was not quite through. Several weeks later, after a plank catwalk had been strung across, he chose to demonstrate its strength in an even more memorable fashion. He leaped into a small carriage, gave his horse a slap of the reins, and went rolling headlong out onto the little bridge, which as yet had no guardrails and which swayed fearfully beneath horse, carriage, and Ellet, who drove standing up, like a charioteer. Everyone watched aghast, women fainted it is said, and Ellet and his bravado became a legend that would last longer at Niagara Falls than anything he built there.

In less than a year he had an angry falling out with the men who were paying for the job. He had finished the catwalk the summer of 1848 and opened it to the public. Very quickly it became a surprisingly lucrative property. Tolls collected came to five thousand dollars before a year had passed and a dispute arose as to whom the money belonged. Feelings between Ellet and his clients got so bad that Ellet drew up cannon at both ends of the bridge, proclaimed it was his, not theirs, and threatened to flatten anybody who came near. There had followed a few tense days at Niagara. Then, inexplicably, Ellet walked away from the greatest opportunity of his career, never to come back, leaving everything he had accomplished swinging uncertainly in the winds of the gorge.

Two years later Roebling commenced his own bridge at the same spot. In temperament and behavior he and Ellet were about as different as two men passionately committed to the same idea could possibly be. Where Ellet talked like a rain maker, Roebling was eloquent but precise, never promising more than he could deliver. Where Ellet was bold, impulsive, dramatic, Roebling was painstaking, methodical, working out every detail in advance. And once he had settled in his mind that he could do a thing, Roebling stuck to it. “Before entering upon any important work, he always demonstrated to the most minute detail its practicability…and when his own judgment was assured, no opposition, sarcasm, or pretended experience could divert him from consummating his designs, and in his own way.”

Roebling started his bridge in 1851 and it took him four years. He worked carefully, steadily, and there were no hair-raising escapades anyone would remember later. For Roebling the excitement of the work, the drama of building a bridge, were chiefly matters of the intellect and spirit. Physical dangers were part of the job, inevitably, but to be taken as they came, or, better still, avoided entirely if a safer way could be figured. The bridge he built was a thorough demonstration of theories he had been perfecting and preaching for a decade and more. “The only real difficulty of the task,” he wrote, “appears to be its novelty.”

Put in its simplest form, Roebling’s fundamental belief about suspension bridges was that the
stiffer
and
heavier
the roadway could be made, the more stable the bridge. To many this seemed contrary to common sense, since the weight of the roadway and its superstructure would seem to jeopardize those very elements that made a suspension bridge a suspension bridge—the cables.

Roebling was not the first to recognize the importance of a heavy, stiff roadway, just as he was not the first to use anchor stays or to spin his cables in place, all things he would be credited with initiating and reverently praised for by some of his more ardent admirers. James Finley had used stiffening beams and railings before Roebling was born and he knew the purpose they served. The scowling little Brunel, trudging about his bridges in a stovepipe hat, had directed that tension cables be attached to counteract the action of the wind. The French engineer Seguin wrote in 1824 that rigidity of the bridge floor was the surest means to prevent the “vacillations arising from moving loads of any considerable mass” and said the best way to achieve that rigidity was an arrangement of strong trusses.

There were others, too, including an English engineer named Rendel, who wrote the following before John A. Roebling had built a bridge:

In the anxiety to obtain a light roadway, mathematicians, and even practical engineers, had overlooked the fact that when lightness induced flexibility and consequently motion, the force of the momentum was brought into action and its amount defied calculation. The author has long been convinced of the importance of giving to the roadway of suspension bridges the greatest possible amount of stiffness…

 

But unlike most every builder of suspension bridges then, and some much later, Roebling not only understood these ideas, he applied them, his system of inclined, or diagonal, stays being an excellent case in point. “I have always insisted that a suspension bridge built without stays is planned without any regard to stiffness, and consequently is defective in a most important point.” And equally important, he did
not
apply some of the other theories in circulation at the time, many of them very bad theories, that were often taken seriously by the supposed experts. So if he cannot be honestly credited with originating all he preached, he at least was the one engineer who was practicing it properly.

In his original letter of proposal to the railroad men, Roebling had written that his bridge over the Niagara Gorge would stand up under a moving train because he would make it stiff enough to do so. He designed the two floors of the bridge and the open timber trusswork that was to bind them together as one enormous “hollow straight beam.” The timber would be well seasoned, well painted, and the upper floor, where the trains would cross, would be caulked and painted as thoroughly as a ship’s deck, and serve thereby, like the roof of an old-fashioned covered bridge, as a protective shelter for the lower floor and the trusswork.

To make the wire cables sufficiently strong to carry such a structure, as well as the trains, was, he said, “a matter of unerring calculation.” So he had calculated (unerringly, he knew) and he had proceeded to build. Few other engineers gave him any hope of success. The most frequently quoted remark was one made by the great English engineer Robert Stephenson, builder of the famous Britannia railroad bridge, a tubular iron bridge, over the Menai Strait (the trains ran through a succession of enormous iron boxes set on stone piers). Stephenson wrote to Roebling from England: “If your bridge succeeds, then mine have been magnificent blunders.”

Roebling had not a doubt in the world that Stephenson was wrong and said so. As far as he was concerned no Englishman, not even Telford, had ever built a suspension bridge worthy of the name; and to his way of thinking there was only one individual who had, or who really understood the subject, and that of course was John A. Roebling.

Then in May 1854 came the news from Wheeling that Ellet’s Ohio River bridge had gone down. It had lasted just five years. As might be expected, the news created a great stir at Niagara Falls. Roebling especially was anxious to know exactly what had happened.

The details were provided in this vivid account published in the Wheeling
Intelligencer:

About 3 o’clock yesterday we walked toward the Suspension Bridge and went upon it, as we have frequently done, enjoying the cool breeze and the undulating motion of the bridge…We had been off the flooring only two minutes, and were on Main Street when we saw persons running toward the river bank; we followed just in time to see the whole structure heaving and dashing with tremendous force.

For a few minutes we watched it with breathless anxiety, lunging like a ship in a storm; at one time it rose to nearly the height of the tower, then fell, and twisted and writhed, and was dashed almost bottom upward. At last there seemed to be a determined twist along the entire span, about one half of the flooring being nearly reversed, and down went the immense structure from its dizzy height to the stream below, with an appalling crash and roar.

For a mechanical solution of the unexpected fall of this stupendous structure, we must await further developments. We witnessed the terrific scene. The great body of the flooring and the suspenders, forming something like a basket swung between the towers, was swayed to and fro like the motion of a pendulum. Each vibration giving it increased momentum, the cables, which sustained the whole structure, were unable to resist a force operating on them in so many different directions, and were literally twisted and wrenched from their fastenings…

 

From the description Roebling understood perfectly what had gone wrong. In a letter to the railroad officials describing his plans for the Niagara Bridge, Ellet had written “…there are no safer bridges than those on the suspension principle, if built understandingly, and none more dangerous if constructed with an imperfect knowledge of the principles of their equilibrium.” Ellet’s own knowledge had turned out to be imperfect, plainly enough. What Ellet had underestimated, Roebling knew, was the importance of building great rigidity into the bridge floor. A heavy floor would be less likely to move in a high wind, but weight alone was not enough. In fact, it was the weight of Ellet’s bridge that had destroyed it, which Roebling later explained in his final report on the Niagara Bridge.

BOOK: The Great Bridge
13.29Mb size Format: txt, pdf, ePub
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