VOCABULARY:
Abutments: On either side of the bridge, these connect the span to the ground. Arch bridge: A bridge using an arch underneath the deck for support. Beam bridge: A bridge supported by piers and a horizontal beam to support the deck. Compression: A force that shortens structural members, pushing them together. Dead weight: How much the bridge weighs. Deck: The road/sidewalk surface of a bridge. Keystone: The central, wedge-shaped stone at the top of an arch that locks the arch together. Load: The weight of the vehicles and people that cross a bridge. Piers: Vertical supports of the bridge, these provide a base for the bridge deck. Span: The distance between the two piers or other vertical supports. Suspension bridge: A bridge with cables suspended from tall piers. The cables hold the deck in place. Tension: A force that lengthens structural members, pulling them apart. Truss bridge: Type of beam bridge that contains a structure made of triangles. |
Objectives1.Bridges are categorized into three primary types: suspension, beam, and arch.
2.Each is designed and built according to certain principles of engineering.Materials Students will need research materials on bridge engineering, including a computer with Internet access. Each group will need the following materials: •Twenty drinking straws •One meter of masking tape •Two stacks of books or blocks of wood •Meterstick •Jar of penniesProcedures 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:
3.Allow each group one class period to research bridge engineering. They should find out 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 (New York City, for example) 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. 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. |