Side-to-Side: How do Buildings Respond to Lateral Movements Produced by Earthquakes?
How do buildings respond to lateral (side-to-side) movements produced by earthquakes?
- 1 sheet of coarse (rough) sandpaper
- Slinky™ or similar toy
- Place the sandpaper on a table.
- Stand the Slinky on end on the sandpaper.
- Grab the edge of the sandpaper with your fingers, and quickly pull the paper forward about 6 inches (15 cm).
- Observe the movement of the Slinky.
The bottom of the Slinky is pulled to the side. The top section of the Slinky temporarily lags behind, and then springs back into place.
The bottom of the coil is pulled to the side by the movement of the paper beneath it. A similar movement occurs during an earthquake, when the ground below a building moves laterally (sideways). These lateral movements are very destructive, since they cause the walls to bend to one side. Inertia (the tendency of an object at rest to remain at rest) holds the upper part of the coil or a building in a leaning position for a fraction of a second, and then the structures snap back into their original shapes. During a typical earthquake lasting only 15 seconds, a building may bend and snap between 15 and 100 times, depending on its structure.
- Earthquakes do not wait for one wave of energy to make a complete ground-to-roofto- ground cycle before the next wave of energy enters the building. What would happen if the Slinky received energy waves from different directions? Repeat the experiment, but jerk the paper back and forth. Science Fair Hint: Use diagrams and/ or photographs along with a written description of the results as part of a science fair project.
- Would a taller building be more affected? Repeat the experiment, using a longer coil (connect two Slinkys). Science Fair Hint: Tape a paper representation of a skyscraper to the Slinky. Display the model and photographs or diagrams indicating the changes to the building during and after the seismic (earthquake) tremors.
Demonstrate inertia by placing the end of a 2-by-12-inch (5-by-30-cm) strip of wax paper under a glass of water. Hold the free end of the strip in your hand, and pull the paper out from under the glass with a quick, straight, forceful movement. NOTE: This may take a little practice, so be sure to place the glass about 6 inches (15 em) from the edge of the table to prevent it from falling off If you pull too slowly, the glass moves forward.
Check It Out!
Find out more about the erratic movement of structures such as buildings or bridges during an earthquake.
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