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  • In the mid-19th century,

  • suspension bridges were collapsing all across Europe.

  • Their industrial cables frayed 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 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 480 meters

  • 1.5 times longer than any previously built suspension bridge.

  • Since standard hemp rope would tear under the deck's 14,680 tons,

  • his proposal called for over 5,600 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 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.

  • 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."

  • 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.

  • 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 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 400 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.

In the mid-19th century,

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史上最も壮大なエンジニアリングの偉業の一つ - アレックス・ゲンドラー (One of the most epic engineering feats in history - Alex Gendler)

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    Taka   に公開 2021 年 01 月 14 日
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