Engineering Application: Designing an Earthquake-resistant structure
Natural disasters such as earthquakes can be exciting to study as science topics but they also can be very devastating to a community when they happen. Buildings, houses, bridges, roads, underground water lines are all vulnerable to earthquakes. In many cases the disaster is the result of poor building practices. Some cultures, which exist in earthquake prone regions, have evolved sophisticated or efficient engineering systems as a method for dealing with such events. In this activity students will take part in an engineering design experience that allows them to observe how sudden acceleration as experienced during a seismic event can lead to structural failure and discover what building characteristics most affect stability.
- Explore how earthquakes cause structures to move quickly
- Understand how sudden acceleration causes buildings to fail
- Discover what variables affect building stability
- Engineer a model building to withstand earthquakes better
Two 45 minute class periods. Time will vary since students will be working independently.
- Stackable boxes: Enough for 5-8 boxes per group. They should be roughly cubic in shape and relatively light. Cafeteria milk cartons should be effective if stacked on their sides. Anything that fits that description should work fine.
- Miscellaneous materials: Be prepared each group with the following items if they request them: metal washers, pieces of cardboard, pipecleaners, paperclips, toothpicks, and tape.
- Shake table: One per group would be wonderful, however a classroom table will work as well. They can be built as a class activity or prepared beforehand. Here are some suggestions:
- Making A Shake Table: A flyer developed by the Multidisciplinary Center for Earthquake Engineering Research (MCEER) than outlines some alternatives for building a fairly sophisticated shake table.
- Build it from scratch: Enclose a few golf balls, tennis balls, marbles or tubing within two pieces of cardboard or plywood and secure with three rubber bands as shown in the picture below. The challenge will be to find a method for standardizing the intensity of the vibrations. Either assign one student from each group or one student from the class to develop 2 different vibration levels. Another alternative is for the teacher to develop the standard and perform all the tests.
- A piece of rug can be an inexpensive and easy-to-find substitute. Students need only establish a method for shaking the rug evenly. This will be challenging to use and not a preferred approach but it is easier to come by and much less expensive.
- Vibratory tables can be purchased from the following websites:
- The Discovery School website has an activity that outlines the building of a shake table out of PVC tubing and wood and they include an activity!
- Divide students into teams of 2-4 students per team.
- Teams should perform the following instructions:
- Stack 2 boxes on the shake table .
- Move the shake table moderately. This needs to be established by the teacher and standardized as best as possible.
- Observe what happens.
- Add another layer to the structure .
- Observe what happens.
- Continue increasing height until structure fails.
- As a class note the highest structure that can survive moderate shaking.
- Brainstorm the answer to the following question: What characteristics about the motion causes the "building" to be displaced or collapse?
- Discuss the students observations. Be sure the following conclusions are arrived at:
- Earthquakes cause buildings to move quickly.
- This sudden acceleration causes buildings to want to “fly off” the earth.
- The sudden acceleration can lead to failure
- Failure is caused by the shear force between the earth and the building and by the frequency of the vibrations.
- Next explain the engineering design process: Discuss the different steps in the process and why each step is important.
- Identify problem: Identify what is needed.
- Research: Identify what knowledge and resources can be used to solve problem.
- Develop solutions: Make designs of possible solutions.
- Select best solution out of possible designs.
- Construct prototype: Build selected design.
- Test and evaluate solution: Test prototype in appropriate setting, record observations.
- Communicate solutions: If necessary, present prototype and report observations. The design process can stop here if engineer does not wish to refine the prototype.
- Redesign: In order to have a more useful prototype, the engineer has to redesign original prototype based on results from testing. To redesign, start at the beginning of the cycle.
- Have groups develop a list of possible methods for increasing stability. A list of materials might include: small weights (like hardware store metal washers), cardboard, pipe cleaners, toothpicks, and paper clips. Create a price list so that students can develop a cost analysis of their design. For example:
- small weight, $5
- piece of cardboard, $1
- pipecleaner or paper clip, $0.50
- toothpick, $0.25
- piece of tape, $5
- Remember Step 2 when the class agreed to a maximum height which could withstand a moderate earthquake? The goal for each group is to design and build a freestanding at the maximum height in Step 2 plus the addition of two more layers that can withstand a moderate earthquake. Note: if you are not working with a vibratory table that has specific settings to use have a standardize system for generating the same intensity earthquake for each trial.)
- Parameters are as follows:
- The total mass of the structure may not exceed 3 kilograms.
- The individual boxes cannot be attached to each other.
- Have the students test some of the ideas for improving structural stability. Students should be encouraged to reiterate their design and log their experience.
- Next, have students demonstrate and present their design for evaluation. Students should be prepared to discuss the following issues:
- Successes and failures in their experience
- Engineering benefits of their design
- Cost of their building