Transcript
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CABLE-SUSPENDED
BRIDGESENGLISH CLASS
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Few structures are as universally appealing as cable-
supported bridges. The origin of the concept of bridging
large spans with cables, exerting their strength in tension,
is lost in antiquity and undoubtedly dates back to a time
before recorded history. Perhaps primitive humans,
wanting to cross natural obstructions such as deep
gorges and large streams, observed a spider spinning a
web or monkeys traveling along hanging vines.
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EVOLUTION
Early cable-suspended bridges were footbridges consisting of cables
formed from twisted vines or hide drawn tightly to reduce sag. The
cable ends were attached to trees or other permanent objects located
on the banks of rivers or at the edges of gorges or other natural
obstructions to travel. The deck, probably of rough-hewn plank, was
laid directly on the cable. This type of construction was used in
remote ages in China, Japan, India, and Tibet. It was used by the
Aztecs of Mexico, the Incas of Peru, and by natives in other parts of
South America. It can still be found in remote areas of the world.
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The first metal suspension bridge in North
America was the Jacobs Creek Bridge in
Pennsylvania, designed and erected by James Finley
in 1801. Supported by two suspended chains of
wrought-iron links, its 70-ft span was stiffened by
substantial trussed railing and timber planks.
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A major milestone in progress with wire cable was
passed with erection of the 1,010-ft suspended span
of the Ohio River Bridge at Wheeling, Va. (later
W.Va.), by Charles Ellet, Jr., in 1849. A second
important milestone was the opening in 1883 of the
1,595.5-ft wirecable- supported span of the
Brooklyn Bridge, built by the Roeblings.
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The first use of a pure stayed bridge is credited to
Loscher, who
built a timber-stayed bridge in 1784 with a span of 105 ft
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The pure-stayed-bridge concept was apparently not used again
until 1817 when two British engineers, Redpath and Brown,
constructed the Kings Meadow Footbridge with a span of about 110
ft.
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DespiteNaviers adverse criticism of stayed bridges, a few more
were built shortly after the fatal collapses of the bridges in England
and Germany, for example, the Gischlard- Arnodin cable bridge (Fig.
15.2c) with multiple sloping cables hung from two masonry towers.
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In 1840, Hatley, an Englishman, used chain stays in a parallel
configuration resembling harp strings (Fig. 15.2d). He maintained the
parallel spacing of the main stays by using a closely spaced subsystem
anchored to the deck and perpendicular to the principal loadcarrying
cables.
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The principle of using stays to support a bridge superstructure did
not die completely in the minds of engineers. John Roebling
incorporated the concept in his suspension bridges, such as his
Niagara Falls Bridge (Fig. 15.3);
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Rebirth of stayed bridges appears to have begun in 1938 with the
work of the German engineer Franz Dischinger. While designing a
suspension bridge to cross the Elbe River near Hamburg (Fig. 15.5),
Dischinger determined that the vertical deflection of the bridge under
railroad loading could be reduced considerably by incorporating cable
stays in the suspension system.
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AKASHI KAIKO JAPANAKASHI KAIKO JAPAN 1990M1990M
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STOREBELTSTOREBELT ZEALANDZEALAND--SPRAGOSPRAGO,,
DENMARKDENMARK 1624M1624M
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HUMBERHUMBER RIVERRIVER HULL,HULL, ENGLANDENGLAND
1410M1410M
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THANX
ANY QUESTIONS?ANY QUESTIONS?
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