Weston Middle School
Technology/Engineering Course Materials
Prep:
- Corrugated strips 4 " wide
- Corrugated Squares 4" square
- Glue guns
- Mylar tape
- scale
- photos of bridges
- posts and panels
- bricks
Review Concepts :
- Tension and Compression in Beams- sponge demo
- Efficiency= Live Load/Dead Load
- Simplest Bridge- Beam Bridge- cheap, easy to make
- Demo: Efficiency of cardboard strips
- Anatomy of I-beam,
H-beam
Why are beams stronger when they are vertical rather than flat?
What holds a beam up?
Look at broken beam, sponge, beam model
Force downwards causes compression in top of beam, and tension in bottom of beam
Downwards force becomes a sideways force, resisted by the tensile strength of the beam—structural beams have wide flanges to provide extra material at point of greatest stress, and little material in middle (web) where forces are minimal
The wider the web, the less the force on the bottom flange.
Beams are efficient
Greek temples had stone posts and beams.
Stone is strong in compression, but weak in tension- stone lintels easily cracked. So lots of columns were needed.
Demo: Styrofoam-beams
Romans developed the arch ( rebuild model ), which transmits the load to the ground in compression only- can span large distances.
Many beam bridges have a slight arch ( camber) to reduce tension on beams
Activity for Groups:
- Hot-Glue Box-Beams, posts ; glue beams into pairs
- Assemble into bridges( 3 per deck)- overlap deck
- Test strength with water bottles
- Combine into long bridge using posts and duct tape
- Test with student as weight
- What is the limitation of post-and-beam bridges?
