Tension and Compression Demonstration

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Tension and Compression Demonstration
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The Basic Truss

• Three links are connected by pin joints forming a
  truss.
• Loading the peak of the truss by a vertical load
  results in some members to undergo compression
  while others experience tension.
• Force analysis can tell us which members are in
  tension, and which are in compression.
• Question What is meant by compression and
  tension?
• This module will demonstrate what the terms
  describe in regards to the action that the member
  experiences.

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The Truss

• All links are the same length.
• Link A is under tension.
• Links B and C are under compression
• Question Is it apparent what the loading is in
  each member?

Link B
Link C
Link A
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Replacing Link A

• To demonstrate that Link A is under tension, it
  will be replaced by a member that has a spring.
• Now, applying the vertical load causes the two
  bottom joints to move away from each other.
• When load is removed, the two joints spring back
  toward each other because the new link pulls each
  joint toward each other.
• This is an example of tension.

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Replacing Link C

• Replacing link C by a springy link will
  demonstrate that it is under compression.
• Now, applying the vertical load causes the top
  joint to move toward the bottom joint.
• When the load is released, the spring pushes the
  top joint away from the bottom joint.
• This is an example of compression

Top joint
bottom joint
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Replacing links C and B

• To further demonstrate the idea of compression,
  both links C and B will be replaced by spring
  elements.
• The vertical load causes both links to move
  downward causing the springs to push upward.

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Replacing all the links

• Replacing all the links by springs will show how
  the forces in each link interact with other.
• Observe that links in compression get shorter,
  while links under tension get longer.
• Compressed members push back while tension
  members pull back.