Читать реферат по английскому: "Brooklyn Bridge Essay Research Paper Brooklyn Bridge" Страница 1

(Назад) (Cкачать работу)

Brooklyn Bridge Essay, Research Paper

Brooklyn Bridge The Brooklyn Bridge is a suspension bridge that spans the East River from Brooklyn to Manhattan Island, New York City. Suspension bridges are suspended from cables that are draped between high towers and secured to onshore anchorage that counteract the pull of the cable. The Golden Gate Bridge in San Francisco is one of the longest suspension bridges as well as one of the most well known. The Brooklyn Bridge was the first bridge to use steel for cable wire, and during its construction explosives were used inside a pneumatic caisson for the first time. The masterwork of John Augustus Roebling, the Brooklyn Bridge was built (1869-83) in the face of immense difficulties. Roebling died as a result of an accident at the outset, and his son, Washington Roebling, taking over as chief engineer, suffered a crippling attack of caisson disease (the bends) during the founding of the New York pier (1872). Confined to his apartment in Columbia Heights (Brooklyn), he continued to direct operations, observing with field glasses and sending messages to the site by his wife, Emily Warren Roebling. A compressed-air blast that wrecked a pneumatic caisson slowed the work, as did a severe fire that smoldered for weeks in another caisson. A cable that parted from its anchorage on the Manhattan side crashed into the river, and the fraud perpetrated by a steel-wire contractor required the replacement of tons of cable. The construction of the Brooklyn Bridge was a long process that was repeatedly slowed down by persistent difficulties.The Brooklyn Bridge’s 486-metre main span was the longest in the world until the completion of the Firth of Forth cantilever bridge in Scotland in 1890. Its deck, supported by four cables, carries both automobile and pedestrian traffic. A distinctive feature is the broad promenade above the roadway, which John Roebling accurately predicted “in a crowded commercial city will be of incalculable value.” The four 15 3/4-inch cables are the backbone of the bridge. The decision to use steel instead of standard iron wire was a revolutionary proposal. Steel was regarded as a suspect material, not yet proven over time, as was iron. In fact, at the time of the construction of the Brooklyn Bridge, the use of steel in any structure in Great Britain was illegal. Washington Roebling specified a tested wire strength of 160 ksi (twice that of iron), and required that the wire be upgraded, to resist corrosion by the salt air. Unfortunately, much of the wire that was actually used was not to specifications. The wire contractor had been substituting weaker (and cheaper) steel for the desired crucible-cast kind. While justifiably outraged by the scam, Roebling had initially designed the cable to be six times stronger than necessary. He calculated that the condemned wire was still five times stronger than it had to be, and there was no need to remove the strands already in place. The four cables support a dead weight (the deck and suspenders) of 13,240 kips–3,410 kips per cable. Each cable has an ultimate strength of 24,600 kips, but the maximum load on a single cable rarely exceeds 6,000 kips. The river span is 1,595.5 feet, and the maximum sag over the river is about 130 feet. The length of each supported land span is 930 feet. (Berkley, 37) The Brooklyn Bridge was the largest suspension bridge and the first to be constructed of steel. Engineer John A. Roebling conceived of a bridge spanning the East River while ice-bound on a ferry to Brooklyn. The bridge took 16 years to build, required 600 workers and claimed over 20 lives, including Roeblings’s. Most died of caisson disease (now known as the bends) after coming up from the underwater excavation chambers. When finished, the bridge linked Manhattan and Brooklyn, then two separate cities. (Bergin, 67) When it was completed in May 1883, the Brooklyn Bridge was the largest suspension bridge in the world. It is considered one of the greatest architectural accomplishments of the nineteenth century, and is, in fact, a National Historic Civil Engineering Landmark. Roebling, who proposed that the structure be a suspension bridge, initially oversaw its construction. But he died not long after the work began and his son, Washington, took over. Unfortunately, Washington came down with caisson disease, which disabled him and kept him away from the bridge. His wife, Emily, helped him manage the project’s completion. Construction began in 1870 when pneumatic caissons were floated out into the East River and sunk to the river’s bed. These caissons were hollow chambers that provided workers with a dry place to work because continual air pressure kept the water out. Workers dug at the floor of the river until they reached solid ground on which the arches could be built. Many workers, including Washington Roebling, got “the bends” as a result of leaving the caissons and rising to the river’s surface too quickly. Next, the two arches built of New York limestone and Maine granite were erected, followed by the cables that hold up the framework of the bridge. After the wires were strung properly, the bridge floor, which is 135 feet above the river to allow boats to pass easily underneath, was completed. The bridge opened on May 24, 1883. (Bergin, 71).

Many prefer walking or biking across the Brooklyn Bridge rather than driving. Walkers and bikers use the same walkway in the center of the bridge (although it is divided so that bikers don’t run into anybody). The bridge is usually full of activity, ranging from Brooklyn Heights yuppies going to or from work on Wall Street, to runners and joggers, to out-of-towners coming to the famous bridge for the view. At each of the arches the walkway widens into a large square plank. Plaques on the corners of the plank (which will be on your immediate right and left as you come from either side of the bridge) tell the history of the

Похожие работы