The longest cable suspension bridge is 1,410 meters (4,626').
Because its towers stand exactly perpendicular to Earth's surface, they are 3.
49 cm (1 3/8") out of parallel to allow for the Earth's curvature.
In a plane, two lines perpendicular to the same line are parallel.
Why does this change when you work with a curved surface?
By the way, the Akashi-Kaikyo bridge in Japan, which will opened 1998, is 1,990 meters (6,528') long!
Test compression, tension, and torsion on different materials.
First, take a strip of Styrofoam 10 cm x 38 cm (4" x 15").
Ask someone to hold the ends so you can press down gently on top to test compression.
Hold each end and pull it apart to test tension.
Hold the two ends and twist to test torsion.
What were the results of your tests?
Find materials that are strong in tension, weak in compression, and vice versa.
Concrete supports many of our bridges and overpasses.
How is it holding up?
Ice and road salt affect concrete bridges.
Read "Concrete Solutions" by Gary Stix (Scientific American, April 1993) and "Inside the lab and out, concrete is more than it's cracked up to be" by Richard Wollomir (Smithsonian, January 1994).
What are the pros and cons of building bridges with concrete?
Why is it better than steel?
What is reinforced concrete?
Invite a civil engineer to talk to your class about bridges.
What types of bridges exist in your area?
Which mathematics and science courses did the engineer take to prepare for a career in engineering?
What tools do engineers use to design bridges and other structures?