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6-12

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WGBH

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Design and Construct a Road Sign Support

Students use simple materials to design, build, and test a model of a free-standing structure used to support overhead road signs.

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Lesson Summary

Overview

In this activity, students use simple materials to design, build, and test a model of a free-standing structure used to support overhead road signs. First, students watch a video on the engineering design process. Then the design challenge is defined. Next, students conduct research by looking at and discussing images of sign support structures, observing overhead signs in their own environment, and watching a video about bridge design for comparison. Students also get to see the design process in action, by watching a video of the ZOOM cast building a straw bridge. Students then work in groups to design and build their own sign supports. The final designs are presented and tested to see how they stand up to two different types of loads. From this activity, students gain an understanding of the engineering design process.

Objectives

  • Understand the engineering design process (define challenge, research and brainstorm solutions, choose solution that fits within constraints, design and build solution, test solution, evaluate and redesign if necessary)
  • Recognize the benefit of using triangular shapes in construction
  • Recognize the need to understand the importance of construction technologies

Grade Levels: 6-8, 9-12

Suggested Time

  • Four 50-minute blocks

Multimedia Resources

Materials

  • thick spaghetti noodles (uncooked) or drinking straws
  • glue
  • rulers
  • file folders
  • scissors
  • index cards
  • newspaper (to cover work space)
  • small paper cups
  • string
  • small weights (marbles or coins)
  • fan or hair dryer
  • clay or cellophane tape

Before the Lesson

  • Cut file folders into 1 cm × 1 cm squares.
  • Tie string to paper cups so that they can be hung open side up from the final structures.

The Lesson

Part I

Defining the Challenge

1. Tell students that they will be designing, building, and testing models of the structures that support overhead highway signs. Start with a discussion about the steps they will need to follow. Make a list of these steps, either together as a class or in small groups. Show them the What Is the Design Process? video. Compare and contrast the steps that students came up with to the steps in the video.

2. Have students write a description of the challenge (for example: to design and build a model of an overhead sign support that will remain standing when the wind blows on the sign or when a heavy load is placed on it). This exercise can be done as a class or in small groups.

Brainstorming and Researching the Solution

3. Let students know that they are starting the brainstorming and research component of the design process. Have them view the Road Signs Gallery still images and encourage them to notice the structures used to support the signs. Ask students:

  • What factors must be considered before building a sign support? (Possible answers: It must be high enough so that trucks won't hit it; it must be strong; it must be stable)
  • Where have you seen signs and supports like these?

4. Have students observe sign support structures on their way home from school for discussion the following day.

Part II

More Brainstorming and Research

5. The next time the class meets, discuss the following:

  • What type of sign support structures did you see?
  • Did they cross the road completely or overhang just part of it?
  • What do you think keeps them from collapsing or falling over?
  • What keeps the signs from twisting on their support so that they stay in an upright, readable position?

6. Show students the Train Truss Animation video and the Firth of Forth Cantilever Bridge video, and encourage them to look for similarities in design between the bridges and sign support structures. Ask students:

  • Which types of bridges are similar in design to sign support structures? (Answer: truss bridges)
  • What design element do they have in common, and why do you think it is used? (Answer: triangles, because they are strong shapes)
  • What are some of the differences in design that you notice between bridges and sign support structures?

7. To help the students understand the strength of triangles, have them explore the Shapes Lab interactive activity.

8. To review the engineering design process, show the Triangles: Designing a Straw Bridge video. Ask students:

  • What steps of the design process did the ZOOM cast use to build their straw bridge? (Answer: design, construction, evaluation, and redesign)
  • How do you think the information on the video will help you when you build your sign support structures?

Design and Sketch Solution(s)

9. Divide the class into small groups and have them draw pictures of the sign support structures that they want to build. Give them the following design specifications: road width = 40 cm; maximum truck height = 15 cm; number of signs = 1 large or 2 small. Then have the each group review their designs and choose one to build.

Part III

Construction

10. Have students cover their workspace with newspaper. Then pass out the materials groups will use to build their sign support structure. The structure should be built by gluing the material to the 1 cm × 1 cm squares. See example:Straw Structure Diagram This allows for easy cross-member attachment. The index cards are to be used as the signs. Encourage students to share the tasks and work collaboratively on the building process.

11. Allow time for the structures to dry before setting up and testing.

Part IV

Testing/Evaluation

12. After the sign support structures are dry and the index card signs are in place, have each group present their model to the class. Tell them to include the following information:

  • why they picked this particular design for their structure
  • a sketch with arrows indicating the tension and compression forces
  • how well they think the structure will hold up under the wind and weighted load tests

13. Test the structures, as follows:

  • Wind load test: Set up the sign support structure, holding it in place by anchoring the column(s) in clay or taping them to a desk and blow air at the sign(s). (If possible, use a fan or a hair dryer on the lowest setting.)
    • Does the structure blow over or remain standing?
    • How strong a wind force can it withstand?
  • Weighted load test: Set up the sign support structure again. Select a location farthest from the structure's vertical support(s) and attach a small paper cup by a string, so that the cup hangs straight down but does not touch the "ground." Load the cup with weights (marbles or coins), one by one.
    • How much weight can the structure hold before collapsing?
    • Do the sections look as if they are acting in tension and compression, as predicted in the sketch students presented to the class?

14. Have students evaluate the results of the load tests by discussing the following:

  • What would they do differently in their next design?
  • Were some steps in the engineering design process more important than others? Explain.

Check for Understanding

Discuss the following:

  • What are the steps in the engineering design process?
  • Much can be learned from structures that fail. What did you learn from your test results?
  • How was your design similar to or different from the other designs in the class?
  • What would you do next time to make your structure stronger or lighter?

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