Transcript History of Bridges

Forging new generations of engineers
History of Bridges
Bridges
In the Beginning……...
Natural Bridges
Bridges
The first man made bridges:
Simple beam bridge
Logs formed the beams
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
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
With arches, everything is in
compression all the time
Bridges
As with simple beam bridges, long spans can
be realized by using multiple arches
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.
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.
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
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.
Bridges
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.
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
Bridges
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.