Transcript Structures - Sault College

What is a Bridge?
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A Structure across an obstacle to allow safe
passage
The Sault Ste. Marie International Bridge made
traveling across the St. Mary's River and the Soo Locks
much more desirable.
Mackinac Bridge
The Mighty Mac
London Bridge
Confederation Bridge
Loads: Dead or Alive
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Two categories of loads try to destroy structures. They are
known as:
 Dead loads, and
 Live Loads
Dead loads are the permanent loads on a structure. For
example, the self weight of a bridge
Live loads are all the variable loads, those that occur from time to
time. For example, your weight in the classroom
Loads: Dead or Alive
List Loads
Dead
Live
Completion Of Bridge Loads
Live Loads
Dead Loads
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Self-weight
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Concrete, steel, asphalt
Lights
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Pedestrians
Bikes
Cars
Trucks
Trains
Snow
Wind
Earthquake
Loads Create Forces
Types of Forces
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Tension
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Compression
Tension and Compression
Activity
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Drawings are used by architects and engineers to
communicate important information.
Use your sketching skills to draw the wheel of a
bicycle and a step ladder.
Note on the sketch which components are in tension
and which components are in compression.
Types of Bridges
Beam Bridge2
When something pushes down on the beam, the
beam bends. Its top edge is pushed together,
and its bottom edge is pulled apart.
Sault Ste. Marie International Bridge
Types of Bridges
Arch Bridge2
The arch is squeezed together, and this squeezing
force is carried outward along the curve to the
supports at each end. The supports, called
abutments, push back on the arch and prevent the
ends of the arch from spreading apart.
Arch Bridge
Types of Bridges
Truss Bridge2
Every bar in this cantilever bridge experiences
either a pushing or pulling force. The bars rarely
bend. This is why cantilever bridges can span
farther than beam bridges.
Truss Bridge
Types of Bridges
Suspension Bridge2
In all suspension bridges, the roadway hangs from
massive steel cables, which are draped over two
towers and secured into solid concrete blocks,
called anchorages, on both ends of the bridge. The
cars push down on the roadway, but because the
roadway is suspended, the cables transfer the load
into compression in the two towers. The two towers
support most of the bridge's weight.
Suspension Bridge
Types of Bridges
Cable-Stayed Bridge2
The cable-stayed bridge, like the suspension
bridge, supports the roadway with massive steel
cables, but in a different way. The cables run
directly from the roadway up to a tower, forming a
unique "A" shape.
Cable-Stayed Bridge
Building Materials
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Need to pick the best material
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Wood, plastic, concrete, steel, aluminum
Compare forces that the material must resist
to the properties of the material
Don’t forget Cost
Materials Lab2
Elasticity
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Bridges sway and flex under loads.
But when the loads are removed the bridge
returns to its original shape.
The property that the bridge possess to
return to its original shape is called elasticity.
Elasticity Demonstrated
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Demonstrate, to yourself, the elasticity
behavior of an elastic band by gently pulling
and releasing the tension in it.
An eraser can easily substitute for the elastic
band. But instead of pulling, slightly twist it.
Did you notice how both the elastic band and
eraser returned to their original shape?
Elasticity
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Bridge members don’t experience the extreme
elongation or twist that you noticed with the
elastic band and eraser demonstration.
They experience more moderate shape changes
that are not easily detected by the human
senses unless you pay real close attention.
Next time you are stuck in traffic on a bridge pay
attention to the rocking motion of your vehicle as
a heavy truck goes by in the opposite direction.
Contest Information
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Refer to your handout on contest information
and please feel free to ask questions. Make
sure that you are clear on the following
points:
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materials to be used
construction specifications
judging categories
testing procedure
References
1.
Nova Online, Super Bridge, Build a Bridge
http://www.pbs.org/wgbh/nova/bridge/build.html
2.
BUILDING BIG: All About Bridges
http://www.pbs.org/wgbh/buildingbig/bridge/
3.
West Point Bridge Design Contest
http://bridgecontest.usma.edu/