THINKING BIG : Spanning the Waters : Tower Bridge
Location: River Thames, London
Date: 1886-1894
Builders: Horace Jones, John Wolfe Barry
Description and dimensions: Two 205-foot main towers connect this iron and granite bridge with the shore; it is able to open electrically in 1 1/2 minutes for river traffic and is also acessable to pedestrians.
Construction: Originally the Tower Bridge opened by haudraulic power, taking up to six minutes to open. The wonder of this structure lies in the moving arms, or bascules , which lift to create a passageway for incoming ships. Each of these arms is 162.5 feet long and attached to a huge forged steel axis 21 feet in diameter and 48 feet wide on which the basucles turn. The total weight involved in lifting the arms of the bridge is an astounding 2,400 tons. Contrary to popular belief, the arms are not lifted completely upright but to an 82 degree angle.
The Biggest Bridges
* Suspension: Humber
Location: Hull, Britain
Size: 4,626 feet
Year completed: 1981
* Cantilever: Quebec Railway
Location: St. Lawrence River at Quebec, Canada
Size: 1,800 feet
Year completed: 1917
* Steel Arch: New River Gorge
Location: Fayetteville, West Virginia
Size: 1,700 feet
Year completed: 1977
* Cable-Stayed: Ikuchi
Location: Honshu-Shikoku, Japan
Size: 1,608 feet
Year completed: 1991
* Continuous Truss: Cooper River
Location: Charleston, South Carolina
Length: 1,600 feet
Year completed: 1992
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