What do I need to know to build one

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Bridges
What do I need to know
to build one .
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Types of Bridges

• Arch Bridge
• Beam Bridge
• Suspension Bridge
• Cable Stays Bridge
• Combination Bridge

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The Arch Bridge
Arch bridge construction began in the time of the
Romans and are one of the oldest types of bridges
and have great natural strength. Instead of
pushing straight down, the weight of an arch
bridge is carried outward along the curve of the
arch to the abutments at each end. These
abutments keep the the arch in perfect tension by
preventing it from spreading out.
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The Pont du Gard aqueduct
This is the Pont du Gard aqueduct built by the
Romans over 2000 years ago near Nîmes, France.
Its recent fame has been enhanced by its use in
comercial advertising. Built completely of
precisely cut and stacked stones. Mortar is used
only in its top tier the rest of the stone
structure stays together by the sheer force of
its own weight.
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Restrictions

• When should you use an Arch Bridge?

Use in places where you need a very open
structure over a large span.
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Beam Bridge

• Beam bridges come in many different forms.
  The most basic beam bridge consists of a
  horizontal beam that is supported at each end by
  piers. The weight of the beam pushes straight
  down on the piers.

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Lake Ponchartrain Causeway, LA
This is the world's longest continuous span beam
bridge bridge. The Lake Ponchartrain Causeway is
almost 24 miles long and consists of two,
two-lane sections that run parallel to one
another. The southbound portion was completed in
1956 and is made up of 2243 separate spans.The
northbound portion was completed in 1969 and is
pieced together from 1500 longer spans.
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Restrictions
Beam Bridges are not well suited for locations
that require unobstructed clearance below.
While you can have a series of continuous spans a
single span can rarely span greater than 250
feet
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Suspension Bridge

• Suspension bridges are light weight and strong
  spanning distances from 2,000 to 7,000 feet While
  they are some of the most architecturally
  pleasing they can also be the most expensive to
  build. A suspension bridges name, comes from the
  roadway suspended from cables, extending from one
  end of the bridge to the other. These cables are
  free moving and rest on top of towers. They are
  secured at each end by anchorages which absorb
  much of the tension in the cables.

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Tacoma Narrows Bridge
At the time it opened for traffic in 1940, the
Tacoma Narrows Bridge was the third longest
suspension bridge in the world. It was promptly
nicknamed "Galloping Gertie," due to its behavior
in wind. Not only did the deck sway sideways, but
vertical undulations also appeared in quite
moderate winds.
Click on image to view video
Drivers of cars reported that vehicles ahead of
them would completely disappear and reappear from
view several times as they crossed the bridge.
Attempts were made to stabilize the structure
with cables and hydraulic buffers, but they were
unsuccessful. On November 7, 1940, only four
months after it opened, the Tacoma Narrows Bridge
collapsed in a wind of 42 mph even though the
structure was designed to withstand winds of up
to 120 mph.
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Restrictions.
Can span the longer distances from than most
other bridges. Spanning 2,000 to 7,000
feet. Because of the expense of the cable and
getting it into place, these tend to be the most
expensive to build.
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Cable Stays

• Cable-stayed bridges may look similar to
  suspensions bridges both have roadways that
  hang from cables and both have towers. The
  difference lies in how the cables are connected
  to the towers. In suspension bridges, the cables
  ride freely across the towers, transmitting the
  load to the anchorages at either end. In
  cable-stayed bridges, the cables are attached to
  the towers, which alone bear the load.

13
Sunshine Skyway Bridge
Built in 1988, the Sunshine Skyway is one of the
first cable-stayed bridges to attach cables to
the center of its roadway as opposed
to the outer edges. A 1981 accident in
which a tanker hit a support and knocked out 1261
feet of the old Skyway bridge killing 36,
inspired the construction of a protection system
on this new bridge.
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Restrictions
For medium length spans (those between 500 and
2,800 feet). They require less cable than
traditional suspension bridges. They can be
constructed out of identical pre-cast concrete
sections, and are faster to build than suspension
bridges. They are some of the most
architecturally pleasing bridges.
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• Special thanks to the Nova Online Super Bridges
  site
• http//www.pbs.org/wgbh/nova/bridge/build.html
• for much of this information.