Weston Middle School

Technology/Engineering Course Materials

Weston, Massachusetts
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Grade 7 Design-Construction

 Columns in Tension and Compression Links

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Class Notes




Additional Material

Demo: Compressive Strength of a Paper Cup

See Zoom! Description

Start with 8 paper cups- test-remove 1 -retest- remove 1- repeat----

80 pound student is supported by 4 paper cups

3 paper cups---failure!

Compressive strength of cup = 80/4= 20 lbs


Demo: Compressive Strength of An Egg



Measuring compressive strength of teacher

  • Combining strength in tension and compression:

Put a board on top of 12 oz plastic cups. Invite a student to stand on it( it will collapse). Now fill the cups with wet sand, and repeat- it will hold.

The cup is strong in tension, while the sand is strong in compression. By combining these properties, we get a structure which is strong in both.

This principle is used in constructing columns for post-and-beam highways bridges- an outer sheath of steel reinforcing bar is constructed ( strong in tension, like the paper cup), then filled with concrete, which is strong in compression.

  • This technique was developed following a 1978 earthquake in California, in which many concrete bridges had collapsed.

Science Wing Foundation Walls -Concrete Mixed with Rebar

Soil Testing Apparatus to Measure Compressive Strength of Subsoil

  • Biology Connection:

Skeletal Bones consist of a matrix of collagen fibers, a protein which is stong in tension (collagen is the main component of skin and tendons), similar to rebar.This matrix is then filled in with calcium salts, which are strong in compression, analogous to concrete.

Thus bone, like the highway columns, is strong in both tension and compression.

Demo: Saw open turkey bones.

Social Studies Connection: Roman Concrete

Failure in tension and compression- Laval Overpass Collapse, Montreal, October 2006



Carbon Nanotubes





Microstructure Animations:

Pretest on Concrete

Concrete-Pictorial Timeline

Concrete- Table of Contents


Zoom- Paper Cups

Earthquake Engineering-Wikipedia

Designing Earthquake protection


Revised January 2011 by Jonathan Dietz, dietzj@mail.weston.org