BRIDGES
Beauty and Function
HISTORY
 The first bridges were nature-made: trees that fell
across creeks or rivers.
 The first man-made bridges were most likely made
from trees lashed, stones, or vines.
ROMANS
 Designed amazing arch bridges and viaducts that
could withstand nearly anything when other bridges
continued to fail.
 The Romans discovered the strength of the arch.
 The Alcantara bridge, built in 106 A.D. is still standing
today – almost 2,000 years later!
FORCES ACTING ON A BRIDGE
 Compression – when material squeezes together
 Tension - when material pulls apart
 Bending – when material gets shorter on one side and
longer on the other
 Shearing – when material slides in opposite directions
 Twisting – when the ends of a material twists in
opposite directions
http://www.pbs.org/wgbh/buildingbig/lab/forces.html
BALANCING THE FORCES
 A good bridge keeps all the forces in balance; if there
is compression there is and equal amount of tension.
BRIDGE TYPES
 BEAM BRIDGE
 Made of steel, concrete, or wood
 Typically shorter than 250’
 The longest is the Lake Ponchartrain Causeway, at just
under 24 MILES long!
 TRUSS BRIDGE
 A simple but very strong bridge type made of connected triangle
shapes, called a “truss”.
 The trusses can be above or below the roadbed.
 The World’s longest truss bridge is the Itiksuki Bridge in Japan.
 ARCH BRIDGE
 Arch bridges have “abutments” at each end.
 The weight of the bridge is forced into and supported by
these abutments.
 The longest arch bridge in the world is the Chaotianmen
Bridge in China. It is 5,712’ long!
 SUSPENSION BRIDGE
 The roadbed of a suspension bridge is supported by
cables hanging down from one huge cable spanning
between the vertical towers.
 The road is “suspended” from these cables.
 The world’s longest is the Akashi Kaikyo Bridge in Japan
at 12,825 feet!
 CABLE-STAYED BRIDGE
 Use less cable than a suspension bridge by having taller
towers and cables that connect to the roadbed beneath
it.
 The world’s longest cable-stayed bridge is the Sutong
Bridge in China at 26,923 feet!
Your Challenges
Arch Bridge
Challenge!
Toothpick Bridge
In Engineering Notebook:
1. The challenge: Design and build a bridge with 100
toothpicks and white glue that will cross the West River.
Must be at least 2” wide. Glue cannot be larger in diameter
than a pencil eraser at any point.
2. Ideas: (brainstorm)
3. (Best idea:
4. Build (full-sized sketches work great or you can describe
the steps you’ll take)
5. Test and modify (well….you only get one “test” but you
can put it in place to see how well it fits.
6. Final Test (weight test until broken or an A+).