David McCullough Library E-book Box Set

by David McCullough

  “Lines of steamers, such as the world never saw before, are now plowing the Atlantic in regular straight line furrows,” he had written in his proposal. “The same means of communication will unite the western coast of this continent to the eastern coast of Asia. New York will remain the center where these lines meet.”

  This, in other words, was to be something much more than a large bridge over an important river. It was to be one of history’s great connecting works, symbolic of the new age, like the Atlantic cable, the Suez Canal, and the transcontinental railroad. “Lo, Soul, seest thou not God’s purpose from the first?” wrote Walt Whitman at about this time. “The earth be spann’d, connected by network…The lands welded together.” “The shapes arise!” wrote the Brooklyn poet.

  Singing my days,

  Singing the great achievements of the present

  Singing the strong, light works of engineers…

  But it was Roebling himself, never one to be overly modest, who had set forth the most emphatic claim for the bridge itself and the one that would be quoted most often in time to come:

  The completed work, when constructed in accordance with my designs, will not only be the greatest bridge in existence, but it will be the greatest engineering work of the continent, and of the age. Its most conspicuous features, the great towers, will serve as landmarks to the adjoining cities, and they will be entitled to be ranked as national monuments. As a great work of art, and as a successful specimen of advanced bridge engineering, this structure will forever testify to the energy, enterprise and wealth of that community which shall secure its erection.

  Roebling had written that in 1867, at the very start of his formal proposal, but in all the time since, for some mysterious reason, not a spade of dirt had been turned and numbers of people, some claiming to be experts, had begun saying they were not so sure about Roebling’s “advanced engineering,” or whether it was worth the six to seven million dollars he had said it would cost, an estimate that did not include the price of the land required. Even if his figures were realistic, the bridge would also be about the most expensive ever built.

  The editors of Scientific American said a tunnel would serve the purpose as well and cost less. A Navy engineer presented an alternative plan. He wanted to block off “the vexatious East River” with a dam several hundred feet wide on which he would build highways, stores, docks, and warehouses. By early 1869, when it looked as though the bridge might actually be started, the critics were sounding forth as never before. Warehouse owners along the river and others in the shipping business were calling it an obstruction to navigation and a public nuisance. The New York Polytechnic Society put on a series of lectures at Cooper Union devoted exclusively to the supposed engineering fallacies of the Roebling plan. Engineers expressed “grave apprehension.” The bridge, it was stated on the best professional authority, was a monumental extravagance, “a wild experiment,” nothing but an exercise in vanity. Even in Brooklyn the Union said another bridge and a tunnel besides would probably be built by the time everyone finished wrangling over details and questioned why, for so momentous a public work, only one engineer had been called on and no other plans ever considered.

  So it had been to still such talk that Roebling had assembled his seven consultants and with total patience and candor went over everything with them point by point.

  To begin with it was to be the largest suspension bridge in the world. It was to be half again the size of his bridge over the Ohio at Cincinnati, for example, and nearly twice the length of Telford’s famous bridge over the Menai Strait, in Wales, the first suspension bridge of any real importance. It was to cross the East River with one uninterrupted central span, held aloft by huge cables slung from the tops of two colossal stone towers and secured on either shore to massive masonry piles called anchorages. These last structures alone, he said, would be a good seven stories tall, or taller than most buildings in New York at the time. They would each take up the better part of a city block and would be heavy enough to offset the immense pull of the cables, but hollow inside, to provide, Roebling suggested, room for cavernous treasury vaults, which he claimed would be the safest in America and ample enough to house three-quarters of all the investments and securities in the country.

  The towers, the “most conspicuous features,” would be identical and 268 feet high. They would stand on either side of the river, in the water but close to shore, their foundations out of sight beneath the riverbed. Their most distinguishing features would be twin Gothic arches—two in each tower—through which the roadways were to pass. These arches would rise more than a hundred feet, like majestic cathedral windows, or the portals of triumphal gateways. “In a work of such magnitude, and located as it is between two great cities, good architectural proportions should be observed,” wrote the engineer. “…The impression of the whole will be that of massiveness and strength.”

  His towers would dwarf everything else in view. They would reign over the landscape like St. Peters in Rome or the Capitol dome in Washington, as one newspaper said. In fact, the towers would be higher than the Capitol dome if the dome’s crowning statue of Freedom was not taken into account. So this in the year 1869—when the Washington Monument was still an ugly stone stump—meant they would be about the largest, most massive things ever built on the entire North American continent. On the New York skyline only the slim spire of Trinity Church at the head of Wall Street reached higher.

  The towers were to serve two very fundamental purposes. They would bear the weight of four enormous cables and they would hold both the cables and the roadway of the bridge high enough so they would not interfere with traffic on the river. Were the two cities at higher elevations, were they set on cliffs, or palisades, such as those along the New Jersey side of the Hudson, for example, such lofty stonework would not be necessary. As it was, however, only very tall towers could make up for what nature had failed to provide, if there was to be the desired clearance for sailing ships. And as the mass of the anchorages had to be sufficient to offset the pull of the cables, where they were secured on land, so the mass of the towers, whatever their height, had to be sufficient to withstand the colossal downward pressure of the cables as they passed over the tops of the towers.

  Below the water the towers were to be of limestone and each was to be set on a tremendous wooden foundation, but from the water-line up they were to be of granite. In plan each tower was essentially three shafts of solid masonry, connected below the roadway, or bridge floor, by hollow masonry walls, but left unconnected above the bridge floor until they joined high overhead to form the great Gothic arches, which, in turn, were to be topped by a heavy cornice and three huge capstones. The total weight of each tower, Roebling estimated, would be 67,850 tons, but with the weight of the roadway and its iron superstructure added on they would each weigh 72,603 tons.

  The suspended roadway’s great “river span” was to be held between the towers by the four immense cables, two outer ones and two near the middle of the bridge floor. These cables would be as much as fifteen inches in diameter and each would hang over the river in what is known as a catenary curve, that perfect natural form taken by any rope or cable suspended from two points, which in this case were the summits of the two stone towers. At the bottom of the curve each cable would join with the river span, at the center of the span. But all along the cables, vertical “suspenders,” wire ropes about as thick as a pick handle, would be strung like harp strings down to the bridge floor. And across those would run a pattern of diagonal, or inclined, stays, hundreds of heavy wire ropes that would radiate down from the towers and secure at various points along the bridge floor, both in the direction of the land and toward the center of the river span.

  The wire rope for the suspenders and stays was to be of the kind manufactured by Roebling at his Trenton works. It was to be made in the same way as ordinary hemp rope, that is, with hundreds of fine wires twisted to form a rope. The cables, however, would be made of wire abou
t as thick as a lead pencil, with thousands of wires to a cable, all “laid up” straight, parallel to one another, and then wrapped with an outer skin of soft wire, the way the base strings of a piano are wrapped.

  But most important of all, Roebling was talking about making the cables of steel, “the metal of the future,” instead of using iron wire, as had always been done before. There was not a bridge in the country then, not a building in New York or in any city as yet, built of steel, but Roebling was seriously considering its use and the idea was regarded by many engineers as among the most revolutionary and therefore questionable features of his entire plan.

  The way he had designed it, the enormous structure was to be a grand harmony of opposite forces—the steel of the cables in tension, the granite of the towers in compression. “A force at rest is at rest because it is balanced by some other force or by its own reaction,” he had once written in the pages of Scientific American. He considered mathematics a spiritual perception, as well as the highest science, and since all engineering questions were governed by “simple mathematical considerations,” the suspension bridge was “a spiritual or ideal conception.”

  His new bridge was to be “a great avenue” between the cities, he said. Its over-all width was to be eighty feet, making it as spacious as Broadway itself, as he liked to tell people, and the river span would measure sixteen hundred feet, from tower to tower, making it the longest single span in the world. But of even greater import than length was the unprecedented load the bridge was designed to bear—18,700 tons.

  The long river span was not to be perfectly horizontal, but would bow gracefully, gently upward. It would pass through the tower arches at an elevation of 119 feet, but at the center it would be 130 feet over the water. This, as Roebling pointed out, was thirty feet higher than the elevation fixed by the British Admiralty for Robert Stephenson’s Britannia Bridge over the Menai Strait, built nearly twenty years earlier. Before long, sailing ships would be things of the past, he declared. His bridge therefore would be no obstruction to navigation, only possibly “an impediment to sailing.” As it was, only the very largest sailing ships afloat would have to trim their topmasts to pass beneath the bridge.

  But because of the great elevation of the river span and the relatively low-lying shores, the rest of the bridge, sloping down to ground level, would have to extend quite far inland on both sides to provide an easy grade. The bridge would have to descend back to earth rather gradually, as it were, and thus the better part of it would be over land, not water. Those inland sections of the bridge between the towers and the two anchorages were known as the land spans, and were also supported by the cables, by suspenders and diagonal stays. The ends of the bridge, from the anchorages down to ground level, were known as the approaches. In all, from one end to the other, the Great Bridge was to measure 5,862 feet, or more than a mile.

  The red line Roebling had drawn on the map ran southeast from City Hall Park, in New York, crossing the river not quite at right angles, at that point where the river was returning to its essentially north-south course. At the Brooklyn Navy Yard—over to the right of the red line—the river turned sharply to the left, heading nearly due west, but then it quickly turned down the map again to merge with the harbor. And it was right there, where the river turned the second time, right about where the Fulton Ferry crossed, that Roebling had put his “Park Line” connecting New York, on the upper left of the map, with Brooklyn, on the lower right.

  The precise terminating point on the New York side was at Chatham Street, opposite the park. This was the place for the bridge to come in, he said. For the next fifty years the park would remain “the great focus of travel, from which speedy communications will ramify in all directions.” From there his red line crossed over North William Street, William, Rose, Vandewater, and half a dozen more streets, to the end of Pier 29, then over the river, straight through one of the Fulton Ferry slips, and into Brooklyn. Running parallel with Fulton Street, Brooklyn’s main thoroughfare, the line cut across a patchwork of narrow cross streets—Water, Dock, Front, James—to Prospect, where it bent slightly toward Fulton, terminating finally in the block bounded by Prospect, Washington, Sands, and Fulton, or right about where St. Ann’s Church stood.

  Down the center of the bridge Roebling planned to run a double pair of tracks to carry specially built trains pulled by an endless cable, which would be powered by a giant stationary steam engine housed out of sight on the Brooklyn side. In time these trains would connect with a system of elevated railroads in both cities and become a lucrative source of revenue. He had worked it all out. His bridge trains would travel at speeds up to forty miles an hour. A one-way trip would take no more than five minutes. It was certain, he said, that forty million passengers a year could be accommodated by such a system, “without confusion and without crowding.”

  Carriages, riders on horseback, drays, farm wagons, commercial traffic of every kind, would cross on either side of the bridge trains, while directly overhead, eighteen feet above the tracks, he would build an elevated boardwalk for pedestrians, providing an uninterrupted view in every direction. This unique feature, he said, would become one of New York’s most popular attractions. “This part I call the elevated promenade, because its principal use will be to allow people of leisure, and old and young invalids, to promenade over the bridge on fine days, in order to enjoy the beautiful views and the pure air.” There was no bridge in the world with anything like it. And he added, “I need not state that in a crowded commercial city, such a promenade will be of incalculable value.”

  So the roadways and tracks at one level were for the everyday traffic of life, while the walkway above was for the spirit. The bridge, he had promised, was to serve the interests of the community as well as those of the New York Bridge Company. Receipts on all tolls and train fares would, he asserted, pay for the entire bridge in less than three years. To build such a bridge, he said, would take five years.

  Horatio Allen and William McAlpine asked the most questions during the sessions Roebling held with the consultants. The length of the central span and the tower foundations were the chief concerns.

  It had been said repeatedly by critics of the plan that a single span of such length was impossible, that the bridge trains would shake the structure to pieces and, more frequently, that no amount of calculations on paper could guarantee how it might hold up in heavy winds, but the odds were that the great river span would thrash and twist until it snapped in two and fell, the way the Wheeling Bridge had done (a spectacle some of his critics hoped to be on hand for, to judge by the tone of their attacks).

  Roebling told his consultants that a span of sixteen hundred feet was not only possible with a suspension bridge, but if engineered properly, it could be double that. A big span was not a question of practicability, but cost. It was quite correct that wind could play havoc with suspension bridges of “ordinary design.” But he had solved that problem long since, he assured them, in his earlier bridges, and this bridge, big as it was, would be quite as stable as the others. Like his earlier works, this was to be no “ordinary” bridge. For one thing it would be built six times as strong as it need be. The inclined stays, for example, would have a total strength of fifteen thousand tons, enough to hold up the floor by themselves. If all four cables were to fail, he said, the main span would not collapse. It would sag at the center, but it would not fall. His listeners were very much impressed.

  There were questions about his intended use of steel and about the extraordinary weight of the bridge. Then at one long session they had discussed the foundations.

  Roebling planned to sink two tremendous timber caissons deep into the riverbed and to construct his towers upon these. It was a technique with which he had had no previous experience, but the engineering had been worked out quite thoroughly, he said, in conjunction with his son, Colonel Roebling, who had spent nearly a year in Europe studying the successful use of similar foundations. McAlpine could vouch for the
basic concept, since he had used it himself successfully, although on a vastly smaller scale, to sink one of the piers and the abutment for a drawbridge across the Harlem River. His caisson for the pier had been of iron and just six feet in diameter. Those Roebling was talking about would be of pine timbers and each one would cover an area of some seventeen thousand square feet, or an area big enough to accommodate four tennis courts with lots of room to spare. Nothing of the kind had ever been attempted before.

  How deep did he think he would have to go to reach a firm footing, the engineers wished to know. Would he go to bedrock? And did he have any idea how far down that might be?

  During the test borings on the Brooklyn side, the material encountered had been composed chiefly of compact sand and gravel, mixed with clay and interspersed with boulders of traprock, the latter of which, he allowed, had “detained this operation considerably.” Gneiss had been struck at ninety-six feet. But below a depth of fifty to sixty feet, the material had been so very compact that the borehole had remained open for weeks without the customary tubing. So it was his judgment that there would be no need to go all the way to rock. A depth of fifty feet on the Brooklyn side ought to suffice and the whole operation would probably take a year.

  About the prospects on the New York side, he was rather vague—but it looked, he said, as though bedrock was at 106 feet and there was a great deal of sand on the way down. Still there was a chance that rock might be found closer to the surface. An old well near Trinity Church showed gneiss at twenty-six feet, he noted, and in the well at City Hall the same rock was found at ninety feet. “The whole of Manhattan Island appears to rest upon a gneiss and granite formation,” he said. The greatest depth to which similar caissons had been sunk before this was eighty-five feet. But he was willing to take his to a depth of 110 feet if that was what had to be done. His consultants said they did not think he would find that necessary.