Building the tallest building

In this experiment, you will build your own miniature shake-table which you will use to test your own LEGO buildings. By building structures of different heights, you will test if increasing the height of the structure has an effect on the stability of the building. You also have the option to measure how hard your earthquake table shakes using a smartphone and Google’s Science Journal app. Will your designs be able to take a shake?

Terms and Concepts

You should be familiar with these terms from the introduction:

  • Force
  • Earthquake
  • Tectonic plates
  • Shake table

Additional terms for students using Google’s Science Journal:

  • Seismometer
  • Acceleration
  • Accelerometer

Questions

  • Are short buildings more stable than tall buildings?
  • How will lateral shaking movements affect a building?
  • How can I build a shake-table to test the stability of model buildings?
  • Currently, what is the tallest tower in the world? How was it built?

Materials and Equipment

  • Enough LEGO bricks to build a tower at least 12 inches tall
  • Flat LEGO base plate, approximately 10 inches x 10 inches
  • Square pieces of plexiglass (2), approximately 12 inches x 12 inches
  • Small rubber bouncy balls of the same size, about 1 inch in diameter or less (4)
  • Large heavy-duty rubber bands (2), long enough to stretch around the plexiglass sheets (approximately 6 inches long when laid flat and unstretched),
  • Metric ruler
  • Duct tape
  • Scissor

Experimental Procedure

Note: In this science project you will build your own shake table and test the strength of LEGO towers. Optionally, you can also measure the strength of your simulated earthquakes using a smartphone and Google’s Science Journal app. You will find the instructions on how to measure the earthquake strength here.

Building Your Shake Table and LEGO towers

  1. Cover the edges of the plexiglass sheets with duct tape. This will prevent the sharp edges from cutting the rubber bands.
  2. Place the two plexiglass sheets on top of one another.
  3. “Rubber band” the two together by stretching a rubber band around each end, about 1 inch from the edge of the sheets.
  4. Insert the rubber balls between the boards at each corner, placing them directly under the rubber bands (this will help prevent the sheets from bending).
  5. The shake-table should now be assembled as shown Figure 3.
Diagram of two plexiglass sheets separated by rubber balls at each corner and held together with rubber bands
Figure 3. A simple shake-table design you can use for this experiment.
  1. Attach a large, flat LEGO mounting plate to the top of your shake-table by slipping it underneath the rubber bands. This will be where you mount your structures to the shake-table.
  2. Build a series of LEGO towers of increasing height (if you do not have enough bricks, you can build and test the towers one at at a time). You should use the same base pattern for each tower, so that the size of the tower’s footprint does not change and only the height will be different. You can double check this after you are finished by measuring the length and width of the base of each tower, and they should be the same.
  3. Measure the height of each tower in centimeters (cm) with the measuring stick. Write the height of each tower in a data table like Table 1.
Tower Height Table Displacement (cm) Did it Fall? (Y/N)

Table 1. Example data table.

Testing Your LEGO Tower Stability

  1. To test each tower:
    1. Place it in the center of the top surface of the shake-table.
    2. Have someone else hold the bottom piece of plexiglass firmly in place, or use C-clamps to clamp it to a table so it does not move.
    3. Pull the top layer of the shake-table out of alignment, as shown in Figure 4. Measure the distance between the edges of the two layers and record this value in your data table. This distance is called the “displacement.”
    4. Quickly release the top layer of the shake table and allow the rubber bands to snap it back into place. Does your tower fall? Record your observation in your data table.
Two plexiglass sheets are moved parallel to each other and the displacement between them is measured
Figure 4. How to create displacement to simulate an earthquake with your shake table.
  1. Test each tower with increasing displacement values until you find out when the tower will fall.
  2. Compare your results. Did all of the towers fall at the same displacement values or were there differences? Did tall towers have different values than short towers?

Optional: Measuring Earthquake Strength with the Science Journal app

Scientists use instruments called seismometers to measure the motion of the ground during earthquakes. In this project, you can use a similar (but not identical) device called an accelerometer to measure the motion of the top plate of your shake table. An accelerometer measures acceleration, or how fast an object’s velocity changes. Accelerometers are built-in to many smartphones and video game controllers to give them motion control. You can use an app called Google’s Science Journal to record data with your phone’s accelerometer. To learn how to measure acceleration and how to record data with the app you can review the relevant walk-through tutorials on this Science Journal tutorial page. Then, try out this procedure:

  1. Use LEGO bricks to build walls to keep your phone in place on top of the base plate, as shown in Figure 5. The phone should lay flat with its screen facing up, and it should be held tightly in place, without sliding around. If the phone can slide around and slam into the walls, this will affect your data. Use additional rubber bands as padding if necessary to hold the phone firmly in place.
A smartphone is placed on a plexiglass sheet next to a building made of LEGOs
Figure 5. Phone held in place with LEGO bricks and a rubber band for padding.
  1. Open the accelerometer that works for the direction you would like to measure, based on which way you will displace your shake table (for example, select the X accelerometer if the phone will be shaking side-to-side).
  2. When you pull back the top plate of your shake table, press the record button before you let go.
  3. Press the record button again to stop recording after your shake table has stopped moving.
  4. Crop your data if necessary and zoom in on the part where the table shakes. Your data should look something like Figure 6.
Example graph of acceleration over time
Figure 6. Example data recorded with Google’s Science Journal and a homemade shake table. The x-axis of the graph is time in minutes:seconds and the y-axis is acceleration in meters per second squared.
  1. Add columns to your data table (Table 1) for the minimum and maximum acceleration values.
    1. How do these values relate to the displacement of the top plate of your shake table? In other words, when you move the plate farther and stretch the rubber bands more, do the minimum and maximum accelerations stay the same, get bigger, or get smaller?
    2. How do these values relate to whether or not your building falls over? Are buildings more likely to survive high accelerations or low accelerations?