1. Stable Structures Discovery Activity

2. Tacoma-Narrows Bridge Tacoma-Narrows Bridge collapsing in 1940 Roadway of Tacoma Narrows Bridge twisting violently in a windstorm, Tacoma, Washington, 1940

3. 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?

4. Cause of the Collapse: WINDS OF MORE THAN 40 MILES PER HOUR!

5. 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.

6. 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.

7. 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)

8. Let’s Investigate http://www.pbs.org/wgbh/buildingbig/lab/forces. html

9. 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?

10. Design a Plan Design a plan or blueprint for a bridge Propose the strongest, safest, bridge you can with the least expensive materials

11. 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!