Stable Structures
Discovery Activity
Tacoma-Narrows Bridge
Tacoma-Narrows Bridge
collapsing in 1940
Roadway of Tacoma Narrows Bridge
twisting violently in a windstorm,
Tacoma, Washington, 1940
Brainstorm
• What causes do you think forced this bridge to
wobble and then fall apart?
• Do you think certain weather conditions could
have contributed to the bridge’s collapse?
Cause of the
Collapse:
WINDS OF MORE THAN 40 MILES
PER HOUR!
Other Bridges
that have
collapsed
• Silver Bridge, Point
Pleasant, West Virginia,
1967
• In the worst bridge
disaster in the history of
the United States, 37
trucks and cars fell into
the water when this
bridge collapsed. The
damage was caused by
a broken I-bar, a small
metal beam that
connects the bridge’s
different part.
Other Bridges
that have
collapsed
• Melbourne Bridge,
Melbourne, Australia,
1968
• When constructing the
bridge, engineers and
architects made a
simple mathematical
error that resulted in
the instability in the
bridge’s steel girder
box. When some of the
steel expanded from
the heat, the bridge fell
120 feet to the ground.
Things to consider when
building a bridge…
• 1. Environmental factors: wind, temperatures,
building materials, and shapes used to support
the structure
• 2. Natural forces: weight of a building
pressing down on lower columns
(compression) and natural stretching of
materials (tension)
Let’s Investigate
http://www.pbs.org/wgbh/buildingbig/lab/forces.
html
Questions
• What natural forces might affect your bridge?
How can you compensate for them?
• What materials are most suitable for your
bridge? Keep in mind wear and tear on the
bridge, temperature, wind speed, and
expense.
• How much weight can triangles, rectangles,
and arches support? Which is most suitable for
your bridge? Why?
Design a Plan
• Design a plan or
blueprint for a bridge
• Propose the strongest,
safest, bridge you can
with the least
expensive materials
Create a Model
• Create a 3-D model of
your proposed bridge.
• With a partner you are
going to build a bridge
between two chairs 30
centimeters apart.
• You may use as many
vertices and edges that
you think are necessary.
• CLASS COMPETITION:
• Which group has the
strongest bridge?
• We will test if your bridge
can hold a paper cup with
5 quarters in it. If your
bridge remains intact
after the initial test we
will continue to add
quarters until only one
bridge remains standing!