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Bridges

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by

Frannie Alexander

on 17 March 2015

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Transcript of Bridges

See if you can spot some shapes in this video.
Did you see triangles?
Your mission...
Build a Truss Bridge using K'nex
Your bridge must include two additional supports with a span of 19 inches
Your bridge must be built using triangles.
Everyone must participate equally in the building of your bridge.
Two students will be responsible for building one side
Two students will be responsible for building the platform and supporting beams
Two students will be responsible for building the other side.
Truss Bridge
A typical truss bridge is a simple design made of triangles, used to cross a shorter span. Notice how when the triangles are next to each other, every other one is upside down.
This design allows
more triangles,
making the bridge
even stronger.
What are some shapes you see when you look at a bridge?



A bridge must bear not only the weight of the materials used to make the bridge, but also the weight of any traffic traveling across it. One shape that distributes force effectively is a triangle.

A triangle is stronger than a square because of how a triangle distributes or carries a force. When a load is placed at any vertex (corner) of a triangle, the force is evenly distributed and the shape remains stable. (Science Fair Projects - Bridge Building Basics)
Check out these triangles used in pyramids!

...over 4,500 years ago!
Bridges
References
Andy's Room. (n.d.). Amazing Bridges From Around The World. Retrieved
from www.youtube.com
BDchannel. (n.d.). 10 World Scariest Bridges. Retrieved from
www.youtube.com
Building Bridges Vocabulary (Teacher Document). (n.d.). Retrieved
from http://www.earthwalk.com/wp-content/uploads/bridgesvocabTeacher.pdf
Deconstructing History - The Great Pyramids of Giza. (n.d.).
Retrieved March 4, 2015, from
Footage File. (n.d.). GALLOPING GERTIE TACOMA BRIDGE. Retrieved from
www.youtube.com
Hurley, T. (n.d.). City of Bridges- Pittsburgh. Retrieved from
www.youtube.com
Science Fair Projects - Bridge Building Basics. (n.d.). Retrieved
from: http://www.all-science-fair-projects.com/print_project_1543_148
The Engineering Channel. (n.d.) The Point Pleasant Bridge Disaster.
Retrieved from www.youtube.com
Bridge Vocabulary

Anchorages:
securing devices that are embedded in the solid rock or massive concrete blocks that spread cables over a large area to evenly distribute the load and prevent the cables from breaking free.
Span:
the distance between two bridge supports
Compression:
a force that acts to compress or shorten the thing it is acting on.
Tension:
a force that acts to expand or lengthen the thing it is acting on.
Buckling:
what happens when the force of compression overcomes an object’s ability to handle compression
Snapping:
what happens when tension overcomes an object’s ability to handle tension.
Dissipate:
to spread force over a greater area so that no one spot has to bear the brunt of the concentrated force
Transfer:
to move force from an area of weakness to an area of strength
Truss:
supporting lattice work added to create very tall beams that add rigidity to an existing beam greatly increasing its ability to dissipate the compression and tension
Torsion:
a rotational or twisting force
Deck-stiffening trusses:
a supporting truss system beneath the bridge deck. (Building Bridges Vocabulary (Teacher Document))


Extra! Extra! Read all about it!

side
construction
platform
construction
(make 2 of these)
YOU DID IT!
... now take a look
- how many triangles do you see?
- why do you think this bridge will be strong?
Check for understanding!
1. About how many bridges are in Pittsburgh?

2. What is Pittsburgh’s nickname?

3. Why are there so many bridges in Pittsburgh?

4. What is span?

5. Why are triangles used to build bridges?
Full transcript