Crazy Eights

Your team of technologists has been hired by C. R. Azy and Associates, Civil Engineers, to design a beam to be used in a highway overpass. The goal of this beam is to hold the most weight with a fixed amount of material. Beam designs will be tested by loading a prototype to failure while it spans an eight inch gap. You must provide an informational report of your results showing all of the cross-sections that you tested and specifying which cross-section resulted in the strongest beam.

Achievement

To meet the requirements of your contract, your team will:

  1. Design and construct a beam to span an eight inch gap while supporting a force downward at the center
  2. Demonstrate the performance of each beam by loading it to failure. For each test you should
    • sketch the cross-section of the beam.
    • determine the cross-sectional area (A) of the beam.
    • record the amount of force (F) required to break the beam.
    • calculate the bending moment (M) applied to the beam when it failed.
    • calculate the second moment of area (I) and section modulus (Z).
    • use the elastic flexure formula to estimate the stress at failure (σyield).
  3. Design and construct different beams with the goal of making a stronger beam.
  4. Test each new beam as before.
  5. Do the assigned problems to learn more about material properties.
  6. Plot the many beam properties you have learned against force at failure to see what factors make one beam stronger than another.
  7. Provide your results in an informational report in the required format.

Conditions

Standards

The evaluation of the task will be based on the following

Performance (30 Points)

The performance of your beam will be based on the amount of force your beam carried as compared to the maximum in the lab

30 points – Maximum in lab
27 points – 90% of maximum
24 points – 50% of maximum
21 points – 25% of maximum
18 points – any beam tested

Problems (40 points, 5 points each)

Each problem should be solved in pencil on its own sheet of plain white or engineering paper

1 point for Given, Find, Relationships

3 points for solution correctly laid out

1 point for correct answers including units (may include errors carried forward)

Informational Report (30 Points)

Provide an informational report in the required format. It will be evaluated for content (10 points), organization (5 points), style (5 points), and presentation (10 points) using the standard rubric.

Make sure the report

In addition to the general requirements, use this guidance.

Summary

Write this section last. The summary (or abstract) should be a clear and concise 3 or 4 sentence version of the report. Be sure and include your best result and most important conclusions. Here is a prompt for the summary:

The goal of Crazy Eights was to... Our strongest beam... and it held ___ pounds of force before breaking (fifth best in the class). The strongest beams were those that had the most...

Introduction

Summarize the task for a student who was absent. Be sure and include all rules and limits.

Then explain the math and science involved, including the theory behind your calculations. Define all terms and explain how they are determined.

Details

Tell the whole story from the beginning in several well-organized paragraphs. Tell what you expected each beam to do and how this compares to the results that you got.

Include a sketch of each beam and a table of results.

Make sure that you include enough information to support each of your conclusions.

Conclusions

What were your best results?

Which of these statements is most true? Why?

How does quality of construction effect the results? What other factors effect the outcome? Can you predict the strength of a beam from its configuration? How is this done?

If you could start over again today, what would you do differently?

Make sure you are being specific. Go back to the Details section and make sure that all of your conclusions are supported.


Links

Engineers Edge Explanation
A lesson on Beams
A lesson using slightly different symbols


Resources

ProblemsBlank Data TableEvaluation
Teacher ResourcesDaily Lesson Power Point

Last updated on 9 December 2013 by P. A. Wiedorn