Understanding: Bridges: Teacher’s Guide Grade Level: 9-12
Curriculum Focus: Technology
Lesson Duration: Three class periods
Program Description There’s more to the “why” of bridges than getting to the other side! Here, learn why some are light and elegant, while others are massive slabs; why some are arched and some suspended; why some are concrete and others steel. Don the proverbial hard hat, too, and see up close just how we pull off putting up these enormous structures.
Video Comprehension Questions •
What are some of the primary factors that engineers must consider when designing a bridge? (When designing a bridge, engineers must consider the length of the span, the type of soil or foundation for the bridge towers, necessary access to the site for construction materials, the expected weather, and the bridge's expected traffic, load, and use levels. They must also consider their budget and the aesthetics of the bridge.)
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What are the three primary families of bridges? (The three primary families of bridges are suspension, beam, and arch bridges.)
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What new and innovative technologies did John Roebling develop and implement to make it possible to build larger bridges? (John Roebling provided the technologies that enabled engineers and construction workers to design and build bridges more efficiently. Roebling introduced vertical and slanted steel cables. These developments increased the stability of bridges as they became larger. He also developed a method for threading the steel cables by using special wheels that threaded the steel cable from one end of the bridge to the other.)
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What are some of the advantages of cable-stayed bridges over other types of suspension bridges? (Cable-stayed bridges use a series of diagonal cables attached to one or more towers to support the load of the bridge. Modern cable-stayed bridges usually require less material to build and may support a longer length between towers.)
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The collapse of the Tacoma Narrows Bridge was a catastrophic yet educational event. What were the unique environmental factors that engineers overlooked as they designed this bridge? How did this event change the design of future suspension bridges? (During the design and construction of the Tacoma Narrows Bridge, engineers failed to account for the constant 40-mile-an-hour winds. Pressure from the wind triggered huge oscillations, as well as an incredible twisting motion. Long suspension bridges are not built with horizontal girders that are open along the sides, to let the wind pass through.)
Understanding: Bridges: Teacher’s Guide
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Most modern bridges are made of steel. What are some of the advantages and disadvantages associated with using steel on large bridges? (Some of the advantages of using steel include its strength, its low cost, and its ability to be easily molded and shaped. Some of the disadvantages include the facts that steel cracks or buckles with temperature and that it is easily corroded by salt, water, and debris.)
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The Sunshine Skyway Bridge was struck by a freighter and collapsed on a foggy morning in May of 1980. How was the design of this bridge changed when it was rebuilt to reduce the risk of this type of accident? (The new Sunshine Skyway Bridge was redesigned as a cable-stayed bridge, which allowed the bridge to be built with a high, curving deck and with longer spans between pilings. They changed the orientation of the bridge. The builders also placed rocks and concrete islands called dolphins in front of each of the new pilings.)
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What are some technological improvements that engineers are investigating in an attempt to improve bridge design and safety? (Engineers are investigating the use of remotely operated, fiberoptic sensors that monitor changes and identify possible structural problems with bridges. They are also experimenting with the use of composites as building materials. Composites are ideal building materials because they are high-tech combinations of carbon fiber, resins, and other materials that are lightweight, extremely strong, and resistant to weathering.)
Lesson Plan
Student Objectives Students will understand: •
Bridges are categorized into three primary types: suspension, beam, and arch.
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Each is designed and built according to certain principles of engineering.
Materials •
Understanding: Bridges video and VCR, or DVD and DVD player
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Research materials on bridge engineering
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Computer with Internet access
For each group: •
Twenty drinking straws
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One meter of masking tape
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Two stacks of books or blocks of wood
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Meterstick
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Jar of pennies
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Understanding: Bridges: Teacher’s Guide
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Procedures 1. Divide your students into groups, provide each group with the necessary materials, and challenge each group to build a bridge that will span 25 centimeters. 2. Set the following rules: •
For the two ends of the span, students will use two stacks of books or wood blocks placed 25 centimeters apart.
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The only materials students may use for the bridge itself are 20 drinking straws and 1 meter of masking tape.
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The straws may be shortened, bent, or cut.
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No part of the bridge may touch anything between the two ends of the span.
3. Allow each group one class period to research bridge engineering. In their research, ask them to describe the basic principles of the three main kinds of bridges: suspension, beam, and arch. 4. Allow each group another class period to brainstorm ideas, make sketches, and choose a final design for their bridges. 5. Students will use a third class period to build their bridges with the materials provided. 6. After all bridges have been completed, have students test their bridges by seeing how many pennies they will hold. Students may modify their bridges, at this point, and then see if they will hold more pennies. 7. Have groups present their bridges and testing results to the class. Ask students to speculate about why some bridges were more or less successful than others. What factors went into the strength or weakness of each bridge? What flaws were inherent in the building materials? How were those flaws overcome? 8. Students who enjoyed this activity can try a more challenging level by increasing the span to more than 25 centimeters.
Discussion Questions 1. Suppose all the bridges in a large city such as New York City were closed. What effect would that have on that city? What are some specific ways that people would adapt to not using bridges? 2. Discuss how each of the three basic types of bridges—suspension, beam, and arch—transfers loads from the bridge to the ground. Describe where tension and compression occur on each type of bridge. 3. Many bridges are icons for their city or region. Why do you think people associate certain bridges with certain cities, while other bridges seem unremarkable? 4. Compare and contrast a beam bridge and an arch bridge. List at least three ways they are similar and three ways they are different.
Published by Discovery Education. © 2005. All rights reserved.
Understanding: Bridges: Teacher’s Guide
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5. The U.S. government requires states to inspect and rate all bridges at least once every two years. Describe ways that technology can be used to make monitoring and inspection of bridges more efficient and effective. 6. The earthquake in October 1989 in the San Francisco Bay area caused great structural damage to many of the bridges in the area. What features would you design as part of a bridge to make it better able to withstand an earthquake? Explain your ideas.
Assessment Use the following three-point rubric to evaluate students' work during this lesson. •
3 points: Students worked cooperatively in their groups; carefully prepared plans and sketches; thoroughly researched principles of bridge engineering and applied principles learned.
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2 points: Students worked cooperatively in their groups; prepared plans and/or sketches; researched and applied some principles of bridge engineering.
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1 point: Students had difficulties working cooperatively in their groups; failed to prepare plans or sketches; research insufficient; only a few principles of bridge engineering applied.
Vocabulary composite Definition: Made up of distinct parts. Context: Chemists and engineers are creating strong yet lightweight composite materials that are now being used in everything from tennis rackets to airplanes. resonance Definition: A vibration of large amplitude in a mechanical or electrical system caused by a relatively small periodic stimulus of the same or nearly the same period as the natural vibration period of the system. Context: The magnified sways and twisting of the Tacoma Narrows Bridge were caused by the resonance of 40-mile-per-hour winds and the natural oscillations of the bridge. stay Definition: A large, strong rope usually of wire used to support a mast. Context: One of the diagonal steel stays that supported the bridge broke, but the structure remained standing. tension Definition: Either of two balancing forces causing or tending to cause extension. Context: The heavy weight of concrete and steel causes a great deal of tension on the cables that support a bridge.
Published by Discovery Education. © 2005. All rights reserved.
Understanding: Bridges: Teacher’s Guide
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viaduct Definition: A long elevated roadway usually consisting of a series of short spans supported on arches, piers, or columns. Context: In Europe, there are still viaducts over deep valleys that were built by the Roman Empire.
Academic Standards Mid-continent Research for Education and Learning (McREL) McREL's Content Knowledge: A Compendium of Standards and Benchmarks for K-12 Education addresses 14 content areas. To view the standards and benchmarks, visit http://www.mcrel.org/compendium/browse.asp.
This lesson plan addresses the following national standards: •
Science—Physical Science: Understands forces and motion.
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Science—Nature of Science: Understands the scientific enterprise.
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Technology: Understands the relationships among science, technology, society, and the individual.
National Academy of Sciences The National Academy of Sciences provides guidelines for teaching science in grades K-12 to promote scientific literacy. To view the standards, visit this Web site: http://books.nap.edu/html/nses/html/overview.html#content.
This lesson plan addresses the following national standards: •
Physical Science: Motions and forces
Support Materials Develop custom worksheets, educational puzzles, online quizzes, and more with the free teaching tools offered on the Discoveryschool.com Web site. Create and print support materials, or save them to a Custom Classroom account for future use. To learn more, visit •
http://school.discovery.com/teachingtools/teachingtools.html
Published by Discovery Education. © 2005. All rights reserved.
