Saturday, June 23, 2007

Brooklyn Bridge - New York City, New York

New York City, New York

When it was opened on 24 May 1883, the Brooklyn Bridge, joining the boroughs of urban Manhattan and semirural Brooklyn across New York’s East River, was the longest suspension bridge in the world—twice as long as any previously built. More significantly, it was the first structure of its kind to be supported by cables of galvanized steel wire instead of the usual iron.

From the early seventeenth century through most of the nineteenth, the only transport link between Manhattan and Brooklyn was a ferry service, latterly the Fulton Street Ferry. As early as 1802 the New-York State Legislature had been petitioned to build a bridge between Long Island and Manhattan Island, but it was not until 1857—a decade before the enabling legislation was passed—that serious consideration was given to the project. The German-born engineer John Augustus Roebling had been thinking about an East River bridge since 1852. Supported by influential local politicians Abram Hewitt and William C. Murray, he proposed a suspension bridge, composed of two 800-foot (247-meter) spans linked by a 500-foot (153-meter) cantilever section over Blackwells Island (now Roosevelt Island), close to

the site of the present-day Queensboro Bridge. But the economic depression was followed in 1861 by civil war, two events that delayed the project until 1866.

Then the New York civil engineer Julius W. Adams proposed a suspension bridge, also on a different site from the final structure. In April 1867, under the entrepreneurship of William C. Kingsley, the New York Bridge Company was founded to build Adams’s version of “The New York and Brooklyn Bridge.” His design was superseded a month later by Roebling’s scheme, prepared in collaboration with Wilhelm Hildenbrand. Their respective contributions are unknown, but most of the credit has gone to Roebling. The Bridge Company was a private corporation, but legislation provided that the city of New York might subscribe $1.5 million of the total capital, the city of Brooklyn $3 million, and private stockholders $500,000; in the event, more than 60 percent of the private funding came from Kingsley and his connections.

The total length of Roebling’s bridge, including approaches and land spans, was to be 5,989 feet (1,796 meters); as built, it was some 800 feet (245 meters) longer. The 1,595-foot-6-inch (479-meter) span across the river would enter the tower arches 119 feet (36 meters) above the shore. A clearance of 135 feet (over 40 meters) at midspan would allow even the tallest ships to sail under the graceful arch. Roebling proposed to ran extensions of the New York and Brooklyn elevated, railroad tracks down the center of the bridge; they were to be flanked by vehicular carriageways. Above the railroad he designed an elevated pedestrian path.

In June 1869 the U.S. Army Corps of Engineers approved (over the signature of Ulysses S. Grant) the construction of Roebling’s bridge. Surveying began without delay. Tragedy was just as immediate: while Roebling was locating the Brooklyn tower, a ferry collided with the Fulton slip on which he stood, crushing his foot. Within about a month, his masterpiece barely started, he died of tetanus poisoning. His son, Washington Augustus Roebling, was appointed chief engineer, and William Kingsley assumed superintendence of construction.

In 1870, with the necessary surveying and dredging completed, the foundations of the tower arches were commenced. The two massive timber caissons were built at Webb & Bell’s Greenpoint shipyard and towed 4 miles (6.4 kilometers) to the bridge site. As an indication of size, the smaller measured 168 by 102 feet (50 by 30 meters); built of foot-square (300-by-300-millimeter) flitches of yellow pine, its roof was 15 feet (4.5 meters) and its walls 9 feet (2.7 meters) thick. The hollow structures were sunk to the riverbed, piled with the granite blocks of the tower bases, as workers inside them removed the spoil, laboring in very uncomfortable and extremely dangerous conditions. After fourteen months’ digging, the Brooklyn caisson reached bedrock in March 1871, at just over 40 feet (13 meters) under the riverbed. The caisson on the Manhattan side reached firm soil at almost twice that depth, although it was still thirty feet short of bedrock, by May 1872. The pressures experienced at such depths killed some workers, prompting Roebling’s decision to go no deeper.

Having spent a lot of time in the Manhattan caisson, he also suffered “caisson disease” (commonly known as the bends). His whole body was crippled, and by the end of 1872 he was barely able to speak and beginning to go blind. With his wife, Emily Roebling, he sought treatment at a spa in Weisbaden, Germany, remaining for several months. Then they lived for three years in Trenton, New Jersey, the location of the Roebling wire works. In 1877 they returned to New York and took a house with a view of the bridge. From there, with Emily’s help, Washington Roebling would supervise the remaining phases of construction.

Meanwhile, work continued on the anchorages, towers, and cables. The anchorage at either end of the bridge comprises thousands of tons of masonry, into which are embedded four huge anchor plates, from which 152 anchor bars in each plate take up the enormous tensile loads imposed by the four huge cables that carry the bridge’s superstructure. The granite neo-Gothic towers, designed to resist the compressive loads exerted on them by the cables, took three years to build. The Brooklyn tower was finished in May 1875, and the Manhattan tower the following July. Rising over 276 feet (83 meters) above the river—equivalent to about twenty-eight stories—they

were higher than any building in New York City except the spire of Trinity Church.

In August 1876 the two anchorages were linked across the East River by a wire rope. The spinning of the four bridge cables in situ—two outer ones and two near the middle of the 85-foot-wide (25-meter) bridge—began in February 1877 and was completed on 5 October 1878. The process combined 278 galvanized steel wires into a strand, and nineteen strands were bound into an iron-wire-wrapped cable, almost 16 inches (40 centimeters) in diameter; each cable could support 11,200 tons (10,200 tonnes). Secured at the anchorages and passing over the towers, they hung in a natural curve, or catenary. At the bottom they were attached to the center of the main span of the bridge deck. From the cables, vertical “suspenders,” about as thick as a man’s wrist, supported the deck along its length, assisted by a system of heavy wire ropes radiating in both directions from the towers. Construction of the understructure, the stiffening trusses, and the roadway began in March 1879.

The Brooklyn Bridge, also then known as the Great East River Bridge, was opened on 24 May 1883 when Hewitt formally presented it to the mayors of New York and Brooklyn. He boasted, “The cities of New York and Brooklyn have constructed, and today rejoice in the possession of, the crowning glory of an age memorable for great industrial achievements.” The New York Bridge Company had been wound up in 1874, when, the project was taken over by the cities of Brooklyn and New York. Instead of the promised three, the bridge took thirteen years to build. And, including a little under $4 million for land acquisition, it cost $15 million—at present values, around $1.5 billion—instead of the estimated $7 million. Until the marginally longer Williamsburg Bridge over the East River was completed in 1903, the Brooklyn Bridge remained the longest bridge in the world.

Major reconstruction was undertaken in 1954, when the engineer David Steinman modified the inner and outer trusses and removed the railroad tracks to widen the roadways New approach ramps were built, and augmented in 1969. There has been a major rehabilitation of the main span and the approaches since 1979 and the latest renovation involved emergency redecking completed at a cost of $33.5 million in October 1999. The bridge was designated a National Historic Landmark by the U.S. Government in 1964 and a National Historic Civil Engineering Landmark by the American Society of Civil Engineers in 1972.

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