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2020年
04月30日
20:05 bbbcさん

TED-Ed1211 Epic Engineering : Building the Brooklyn Bridge (技術の金字塔 : ブルックリン橋の建設)

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ブルックリン橋 は ニューヨーク市にある吊り橋。米国で最も古い現役の吊り橋の一つ。
1869年から工期 14年で完成した。 (明治 2年~明治16年のことだからすごい)
吊り橋と斜張橋を併用した三径間吊り橋。 中央支間 486 m、全長1834m、高さ83m。
2層に分かれており、上層は人と自転車、下層は6車線の車道。  

   参考 : 明石海峡大橋は 中央支間 1991m、全長 3911m、高さ約300m、6車線。
        1998年 完成 (工期10年)、世界最長の吊り橋。

学習用 対訳付き動画 ⇒http://tededjphukyu.webcrow.jp/Translation.html?1211

 5分 135wpm (Edge か Chome なら確実に見える)            

字幕 : 開始後 で字幕On/Off、 で言語選択。文字の色やサイズ゙はオプションから。
.     動画を見るとき、 でフルスクリーンに拡大すると見やすい。

下記英文は ブラウザ Chrome のマウスオーバー辞書が使えます。

In the mid-19th century, suspension bridges were collapsing all across Europe. Their industrial cables frayed(擦り切れる) during turbulent weather and snapped under the weight of their decks. So when a German-American engineer named John Roebling proposed building the largest and most expensive suspension bridge ever conceived over New York's East River, city officials were understandably skeptical.

But Manhattan was increasingly overcrowded, and commuters from Brooklyn clogged the river. In February of 1867, the government approved Roebling's proposal. To avoid the failures of European bridges, Roebling designed a hybrid bridge model. From suspension bridges, he incorporated large cables supported by central pillars and anchored at each bank. This design was ideal for supporting long decks, which hung from smaller vertical cables.

But Roebling's model also drew from cable-stayed bridges. These shorter structures held up their decks with diagonal(斜めの) cables that ran directly to support towers. By adding these additional cables, Roebling improved the bridge's stability, while also reducing the weight on its anchor cables.

Similar designs had been used for some other bridges but the scope of Roebling's plan here dwarfed them all. His new bridge's deck spanned over 48 meters— 1.5 times longer than any previously built suspension bridge.

Since standard hemp(麻の) rope would tear under the deck's 14.68 tons, his proposal called for over 5.6 kilometers of metal wire to create the bridge's cables. To support all this weight, the towers would need to stand over 90 meters above sea level— making them the tallest structures in the Western Hemisphere.

Roebling was confident his design would work, but while surveying the site in 1869, an incoming boat crushed his foot against the dock. Within a month, tetanus(破傷風) had claimed his life. Fortunately, John Roebling's son, Washington, was also a trained engineer and took over his father's role.

The following year, construction on the tower foundations finally began. This first step in construction was also the most challenging. Building on the rocky river bed involved the use of a largely untested technology : pneumatic caissons(潜函工法).

Workers lowered these airtight wooden boxes into the river, where a system of pipes pumped pressurized air in and water out. Once established, air locks allowed workers to enter the chamber and excavate the river bottom. They placed layers of stone on top of the caisson as they dug. When it finally hit the bedrock, they filled it with concrete, becoming the tower's permanent foundation.

Working conditions in these caissons were dismal and dangerous. Lit only by candles and gas lamps, the chambers caught fire several times, forcing them to be evacuated and flooded. Even more dangerous was a mysterious ailment called "the bends (潜水病) ." Today, we understand this as decompression sickness, but at the time, it appeared to be an unexplainable pain or dizziness that killed several workmen.

In 1872, it nearly claimed the life of the chief engineer. Washington survived, but was left paralyzed and bedridden. Yet once again, the Roeblings proved indomitable(不屈の) . Washington's wife Emily not only carried communications between her husband and the engineers, but soon took over day-to-day project management.

Unfortunately, the bridge's troubles were far from over. By 1877, construction was over budget and behind schedule. Worse still, it turned out the bridge's cable contractor had been selling them faulty wires. This would have been a fatal flaw (致命的欠陥) if not for the abundant failsafes in John Roebling's design. After reinforcing the cables with additional wires, they suspended the deck piece by piece.

It took 14 years, the modern equivalent of over 4 million dollars, and the life's work of three different Roeblings, but when the Brooklyn Bridge finally opened on May 24, 1883, its splendor was undeniable. Today, the Brooklyn Bridge still stands atop its antique caissons, supporting the gothic towers and intersecting cables that frame a gateway to New York City.
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