A building's ability to withstand earthquakes is dependent upon structural integrity and the substrate on which the building is constructed. While structural integrity during an earthquake is important, designing a building to stay level (not sink or tip or lean) is equally as important. In fact, during the 1989 Loma Prieta earthquake in San Francisco, this was considered the major cause of damage in the Marina District.
The reason for this that during an earthquake, the underlying substrate tends to shift and act more like a thick liquid than it does a solid surface; this process is termed liquefaction. If you stand on the beach near where the seawater rushes up the beach between your toes you will recognize the sinking into the sand sensation you experience. This is very much what liquefaction does to buildings too!
This lesson will challenge students to develop design strategies capable of withstanding liquefaction.
One 45-minute class period. Time will vary since students will be working independently.
Materials (for one set up)
- Student Worksheet
- Student Design Log
- Container, a medium plastic tub will do
- Milk carton, pint size is best
- Level (spirit/bubble level)
- Substrate such as volcanic rock (Fish tank, decorative)
- Quick cement
- Scotch tape
- Popsicle sticks
- Rubber bands
- Aluminum foil
- Paper clips
There are two components to prepare:
Introduce the challenge:
- Separate class into groups of 3-5 students.
- Inform groups of their challenge:
Objective: URGENT UPDATE! REAL ESTATE VALUES IN YOUR TOWN HAVE GONE SKY HIGH. ALTHOUGH A CORPORATION IS STILL WILLING TO DONATE LAND TO YOUR TOWN FOR THE COMPUTER- TECHNOLOGY BUILDING, THE LAND IS SUSCEPTIBLE TO EARTHQUAKE DAMAGE.
Land has been donated to your town to build the computer-technology building. You will be advised of what substrate exists on the land. Your team must design a building that is sturdy enough to withstand a possible earthquake. Only particular materials are available and you will be challenged to be as economical as possible. Therefore, while designing the building your team must consider the materials available, the cost, the substrate that the building will be built upon, and the fact that the building will be in an earthquake zone. The group will be responsible for agreeing on a design, drawing the design to scale, listing materials and cost, and writing a proposal selling the team design idea to the architect on the project. Good luck!
Demonstrate how to conduct trials in the experiment
- Place plastic tub containing substrate on clean, flat table surface with mock building standing inside.
- Align the house so that it is as level as possible.
- Using a light-weight object, such as a pair of scissors or a ruler, and an easy swing tap the side of the plastic tub for 20 seconds (a slight tremor).
- Check the house to see how level it is. Measure the distance it is off-level with a small ruler. If the building tips over, note that the structure is “thoroughly unstable”.
Students engineer better design strategy
- First, give students a Design Log to complete during testing. Have students consider some design ideas that might prevent the building from failing.
- Each design team should select a person to generate all the earthquakes. This will help standardize the earthquakes or make them as similar as possible. This person should perform the same steps as were demonstrated and measure the distance the building was off-level. Try it two or three times to develop some consistency.
- As a team brainstorm some ideas to improve the building’s ability to stay level. See the materials list at the end to determine what choices you have.
However you may attach things to the building.
Remember you cannot:
- alter the architect’s building design
- use any of the volume inside the building
- attach anything to the sides of the plastic tub
- Next choose the best idea, build and test that idea out. Write down the results of your test in the Design Log. Also, calculate a Percent change for your design:
Percent change = [Original X New]/Original X 100
Original = amount off-level without any modifications
New = amount off-level with new modifications
If your answer is positive then you have successfully improved the design. Congratulations!
Finally, consider the additional cost of the building due to these suggested changes.
- Reiterate the group’s design ideas. In other words, attempt to improve your design for the next trial. Can you improve the structure’s ability to withstand a 20 second tremor? Can you make your design modification more economical?
|Other (TBD by teacher)
Prepare an engineering report that reflects your work and illustrates your team’s most economical and viable idea for improving the original building’s ability to withstand liquefaction during an earthquake. Remember, the group will be responsible for drawing the design to scale, listing materials and cost, and writing a proposal selling the team design idea to the architect on the project.
Preparing the Substrate Materials
- Select a substrate for the entire class to use. Volcanic rock found at arts and crafts stores works well as does the rocks used in fish tanks which can be found at a pet shop.
- Pour substrate into the plastic tub, should be a minimum depth of 3 inches.
Preparing the Mock Buildings
Finally you need to create some mock houses for the students to test. Ideally they fit in the plastic tubs easily and are fairly heavy (top heavy if possible); perhaps 100g or so in weight. Here are some steps you can follow to make some mock buildings out of small milk cartons (presumably from the school cafeteria) and cement. Other ideas that operate along the same lines will work similarly.
- Collect, clean and dry 6-7 mik cartons.
- Mix up enough cement mix and water so that you can put a couple of inches in each carton.
- Fill each carton about 1/5 of the way (or 1 inch) with the cement mix. Do your best to fill them equally.
- Allow cartons at least 24 hours to dry.