LESSON PLANS
Critical Load
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This lesson explores the concepts of structural engineering and how to measure the critical load or the maximum weight a structure can bear. Students design and build a structure designed to hold increasingly greater weight, while determining the structure’s critical load.
Age Levels: 8 – 14
Required Materials
Alternative Materials
Alternative Testing Materials
Materials
Alternative Testing Materials
Process
Source: ASCE YouTube Channel
Finding the strongest strength. Learn how different shapes relate to the strength of a structure. (Video 3:34)
Source: PBS Learning Media, Zoom
Earthquake-proof buildings? Explore ideas for earthquake proofing buildings with hands-on design challenges. (Video 5:57)
Design Challenge
You are a team of engineers all working together, using the engineering design process, to design a structure using 12 index cards and tape to hold a minimum of 4 pounds of weight without collapsing. Before testing your structure, make a prediction of the critical load of your structure (the weight at which you think your structure will fail) and write it down.
Criteria
Constraints
Procedure
Student Reflection (engineering notebook)
The lesson can be done in as little as 1 class period for older students. However, to help students from feeling rushed and to ensure student success (especially for younger students), split the lesson into two periods giving students more time to brainstorm, test ideas and finalize their design. Conduct the testing and debrief in the next class period.
What Civil Engineers Do
Civil engineers are problem solvers, meeting the challenges of pollution, traffic congestion, drinking water and energy needs, urban redevelopment, and community planning. This activity focuses on the work of structural engineers who face the challenge of designing structures that support their own weight and the loads they carry, and that resist wind, temperature, earthquake, and many other forces.
Famous Building Failures
The John Hancock Tower in Boston, Massachusetts (right) is said to have been “known more for its early engineering flaws than for its architectural achievement.” Wind-induced swaying was so large, it was said to cause motion sickness for people on the upper-floors. This problem was solved by adding a pair of 300-ton dampers on the 58th floor. Another unrelated but serious problem was that 65 of its 10,344 floor-to-ceiling plate-glass window panes fell out of the building to the ground during construction — luckily no injuries resulted to either workers or passersby!
Efficiency Ratings and Critical Load
The efficiency rating measures the weight that will cause a structure to fail divided by the weight of the structure itself. The most efficient structures are strong and lightweight – a difficult combination to achieve. For example, roofers in areas which experience heavy snows must factor in the weight of a massive snowstorm into designing the strength of the roof. The weight at which a building or structure fails is called the “critical load.”
Internet Connections
Recommended Reading
Writing Activity
Write an essay or a paragraph describing a recognizable building in your town. Include the history, interesting challenges to the building’s engineering, and challenges that the engineers faced in design and construction.
Note: Lesson plans in this series are aligned to one or more of the following sets of standards:
CONTENT STANDARD B: Physical Science
CONTENT STANDARD F: Science in Personal and Social Perspectives
As a result of activities, all students should develop understanding of
CONTENT STANDARD G: History and Nature of Science
As a result of activities, all students should develop understanding of
CONTENT STANDARD E: Science and Technology
As a result of activities in grades 5-8, all students should develop
CONTENT STANDARD F: Science in Personal and Social Perspectives
As a result of activities, all students should develop understanding of
CONTENT STANDARD G: History and Nature of Science
As a result of activities, all students should develop understanding of
Motion and Stability: Forces and Interactions
Students who demonstrate understanding can:
Engineering Design
Students who demonstrate understanding can:
Engineering Design
Engineering Design
The Nature of Technology
Technology and Society
Design
Abilities for a Technological World
The Designed World
Build a Chair Lift
Research and Planning
You are part of a team of engineers who have been given the challenge of building a chair lift to carry a ping pong ball up the mountain (from the floor of your classroom to the top of a desk or chair) using materials provided to you. Your lift must both carry the ball up the mountain and also back down without the ball dropping out. How you design your chairlift and the chair that will carry the ball, and what materials you use are up to you!
Design Phase
You have been provided with many materials from which to design and build your own chairlift and chair. Consider which materials you would like to use, and list them in the box below. On a separate piece of paper, draw a diagram of the system you intend to build.
Parts Required:
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Build it! Test it!
Next build your chairlift and test it. You may share unused building materials with other teams — and trade materials too. Be sure to watch what other teams are doing and consider the aspects of different designs that might be an improvement on your team’s plan.
You may decide to completely change your design when in the manufacturing phase — and you may ask for additional materials, or try different solutions as you build.
Reflection
Complete the reflection questions below:
1) How similar was your original design to the actual chair lift your team built?
2) If you found you needed to make changes during the construction phase, describe why your team decided to make revisions.
3) Was your chairlift able to carry the ping pong ball up and down the mountain without it falling out of the chair you designed?
4) Which chairlift system that another team developed was the most effective or interesting to you? Why?
5) Do you think that this activity was more rewarding to do as a team, or would you have preferred to work alone on it? Why?
6) If you could have used one additional material (tape, glue, wood sticks, foil — as examples) which would you choose and why?