History of Bridges

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Forging new generations of engineers
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History of Bridges
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Bridges
In the Beginning...
Natural Bridges
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Bridges
The first man made bridges Simple beam
bridge Logs formed the beams
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BRIDGES OF SUBSTANTIAL LENGTH CAN BE BUILT
USING A SERIES OF SIMPLE BEAM SPANS
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THE LONGEST BRIDGE SYSTEM IN THE WORLD IS
THE 18 MILE LONG CHESAPEAKE BAY BRIDGE -
TUNNEL. MOST OF THIS SPAN CONSISTS OF
SIMPLE BEAMS
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VIRGINIA BEACH
CAPE CHARLES
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USS Harry S. Truman Builders Sea Trials June
1998
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Bridges
When all a society has to build with is
stone and wood, the individual span lengths
of a simple beam bridge are very short.

• New technology was needed to
• Span greater distances
• Withstand greater loads
• Withstand the effects of weathering

SOLUTION THE ARCH
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With arches, everything is in compression
all the time
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Bridges
As with simple beam bridges, long spans
can be realized by using multiple arches
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Once materials were available to engineers
which could be loaded in tension, a new
type of arch bridge appeared This was
the suspended deck arch bridge.
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Bridges
The need to span increased distances
continued to pressure bridge designers. With
the new material of steel available, with
its superior performance in tension, new
designs made bridges longer and
stronger. Steel made the TRUSS BRIDGE
possible.
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Still, longer spans were required. As
technology developed, and materials became
available, a new variation on an old design
was possible. This dramatically increased the
total span length. This is the SUSPENSION
BRIDGE
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Bridges
The cables of a suspension bridge are not
fixed to the tops of the towers. Rather,
as this photo shows, they are free to
move as the bridge moves.
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Bridges
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The January 17, 1995 Kobe earthquake had
its epicenter right between the two towers
of the Akashi Straits Bridge. The original
planned length was 1990 meters for the main
span, but the seismic event moved the
towers apart by almost a meter. Since
construction of the deck had not yet begun,
the change was easily accommodated in the
slightly altered final design. The towers
of the bridge contain tuned mass dampers
in order to diminish the vibrations in the
structure during earthquakes.
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Bridges
The most recent development in bridge
design does not make any dramatic increases
in span length. Rather, it allows mid-sized
bridges to built with less material,
therefore making bridges more economical to
build and maintain. These are the CABLE
- STAYED bridges
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Bridges
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Bridges
What does the immediate future hold? As
new strong, lightweight synthetic materials
become more common, ever more impressive
bridges will be built. The current next
step is to bridge the Straits of
Gibraltar.