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Activity (Hands-On)Grades 11 - 12

Trust in the Truss: Design a Wooden Bridge

Photos of railroad and road steel truss bridges.Union-Pacific Railroad through 1900’s Truss Bridge over Garcitas Creek, Inez, Texas and 1910 Steel Truss Bridge on Smith Road in Tiffany, Rock County, Wisconsin. Truss bridges were widely used during the late 1800’s and early 1900’s because their low cost, simple analysis, and efficient use of materials

In this activity students design, construct, and test the strength of a wooden truss bridge and satisfy certain conditions like span, strength, and cost. Students perform the truss bridge strength estimation using a graphic interface that determine stress-compression on the truss elements using the method of joints. Students consider their materials’ hypothetical costs and test their constructed bridges to verify load strength. Expect that the bridges can resist at least 90% of their estimated strength and in case of failure, students have to determine the possible causes.

Engineers approach problem-solving in a variety of ways, including fully understanding of a problem, compiling knowledge of all possible variables, and applying their experience to find a solution. Through these concepts, as well as by using the engineering design process, engineers design durable, economically affordable, and safe solutions. Like civil engineers, students must perform the following steps in this activity: take into account the constraints of a problem; verify the strength of the designed structure using a mathematical model; define steps for the construction process; and construct the model according to the design. They also must perform the corresponding corrections or changes as necessary; and test the model to verify its compliance with the requirements.

After this activity, students should be able to:

  • Develop a plan and a schedule for completion of a design and construction project.
  • Perform the appropriate calculations to determine the tensions-compressions produced by loads on the elements of a truss bridge.
  • Select the appropriate materials to build a bridge, keeping in mind strength and cost requirements.
  • Define several engineering terms such as tension and compression, stress, strain and elasticity of materials; identify the truss bridge parts.·      
  • Analyze quantitatively how bridges work under load.
  • Work as a team to construct a model consistent with a design and given specifications.

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