forging new generations of engineers. history of bridges
TRANSCRIPT
Forging new generations of engineers
History of Bridges
In the Beginning……...
Natural Bridges
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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
THE LONGEST BRIDGE SYSTEM IN THE WORLD IS THE 18 MILE LONG CHESAPEAKE BAY BRIDGE - TUNNEL. MOST OF THIS SPAN CONSISTS OF SIMPLE BEAMS
VIRGINIA BEACH
CAPE CHARLES
USS Harry S. Truman
Builders’ Sea Trials
June 1998
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
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.
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
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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2 Km
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.
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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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.
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