Enhance the students' problem solving skills by challenging them to "span the gap." Introduce the concept of triangulation and explain why it is used in bridge and building design.

Associated Standard and CORE Objective:

• 5050-1203 Explore transformations of geometric figures.
  
  

• 1 - Triangle Model Bridge
• 1 - Truss model
• 1 - Suspension Model Bridge
• 1 - 30" stick or branch
• 1 - Square unit
• 1 - Triangle unit
• 1 - Long board
• 2 - Pieces of 4x4 lumber
• 1 - Piece of 2x4 lumber
• 8 - Bridge building sets: wood pieces, bolts, nuts
• 8 - Long boards
•      - Several cars
•      - Pliers
  
  

1. Using two pieces of 4x4 for the river banks to create the gap, pose this question to the students: "If these blocks represent river banks, and we wanted to get across, how would we do it?"
2. Use the stick (represents a log) to show one way to span the gap. Have the students talk about the advantages and disadvantages of the stick/log. "What if I want to get a car across the river?"
3. Use the long piece of masonite to span the gap. Discuss advantages and disadvantages. (Show that weight bends the bridge)
4. Put a 2 x 4 (or other support) under the middle of the long piece of masonite. This is called a cribbing; it is a support. The advantage is that now the car can go across and not get wet, but sometimes these supports fail (knock the 2 x 4 over).
5. So our challenge is to find a way to span the gap that won't have these disadvantages but will support cars.
   
   

• Show the triangle model bridge. Explain that triangles are often used to span gaps because they have such good structural integrity.
• Show the model suspension bridge. Explain that this is another way to span large gaps.
• Show the truss model. Explain that triangles are used in houses and other buildings because of their structural integrity.
  
  

Separate the students into teams of two or three and distribute the bridge building sets.

Challenge them to "span the gap" using the materials given to them. Encourage them to use triangles because they are the strongest structural units but allow them to use other shapes if they want.

Encourage creativity. A successful bridge will span the gap and carry a load (a car).

NOTE: The pliers are for loosening tight bolts, NOT for tightening bolts.

• Publisher's Weekly v242, Sep 04, 95, p.43-4 "Henry Petroski: Bridges as Archetypal Structures" This article reviews Henry Petroski's new book, which examines five bridge builders and how they fought to build their bridges.
• Technology Review: v97, Nov/Dec, 94, p.52-9 "A Short Course in Modern Bridges" Discusses how some of the world's largest bridges in Japan were designed.
• How Bridges are Made by Jeremy Kingston 624.2 K6186 This book describes how bridges are built. It also tells what bridge makers use to make them; profiles who the bridge makers are; and gives plenty examples of the many different types of bridges.
  
  

Career Fields:

Science, Technical

Occupations:

• Architectural and Building Construction Technician: Help architects and engineers plan and design structures. They test materials, build and transport, store, inspect, and use all types of construction materials. Education: Several years experience as manager, supervisor, or craft worker. May have to pass a civil service examination

• Civil Engineer: Plan, design, and oversee the construction and maintenance of roads, railroads, airports, bridges, harbors, channels, dams, irrigation projects, pipelines, power plants, and water supply and sewage systems. They may work in areas of design, research, construction, or teaching. Education: Bachelor's Degree

• Construction and Building Inspectors: Examine the construction, alteration, or repair of buildings, highways and streets, sewer and water systems, dams, bridges, and other structures to ensure compliance with building codes and ordinances, zoning regulations, and contract specifications. Education: Several years experience as manager, supervisor, or craft worker. Having formal training is advantageous.

• Mechanical Engineer: Plan and design tools, engines, machines, and other mechanical equipment. They design and develop power-producing machines such as internal combustion engines, steam and gas turbines, and jet and rocket engines. They also design and develop power-using machines such as refrigeration and air-conditioning equipment, robots, machine tools, materials handling systems, and industrial production equipment. Education: Bachelor's Degree

• Welder: Perform manual welding, in which the work is entirely controlled by the welder, or semi-automatic welding, in which the welder uses machinery. They plan work from drawings or specifications, or by analyzing damaged metal parts, using their knowledge of welding and metals. Construct and repair ships, automobiles, spacecraft, etc. They join beams when constructing buildings, bridges, and other structures, and pipes in pipelines, nuclear power plants, and refineries. Education: Ranges from a few weeks of school or on-the-job training to several years combined school and on-the-job training.

* Taken from Occupational Outlook Handbook 1998-1999.

1. Why are triangular structures used in construction so often?

2. What geometric structures did the students use when constructing their bridges? What worked? What didn't work?
3. What are some common examples of triangulation in everyday structures?
   
   

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Learn about the engineering design process by:

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