Weston Middle School
Technology/Engineering Course Materials
Demo: Compressive Strength of a Paper Cup
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
egg-speriment
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
Microstructures:
Microstructure Animations:
Earthquake Engineering-Wikipedia
Designing Earthquake protection
