# How earthquakes affect buildings: Teachers' notes

Students use a shake table to investigate the effects of earthquakes on structures.

## Learning objectives

Students will:

• observe how some structures vibrate more strongly than others at a given frequency
• recognise that this response can be modified by changing the design of the structure — e.g. by changing its height, the stiffness of the framework, or where the centre of mass is — and by the ground on which it is built.

## Notes

The basic activity on resonance can be extended by looking at the effects on model buildings made from construction kits or craft straws, to see how modifying the design affects a building's ability to withstand an earthquake.

You could also demonstrate liquefaction of ground materials by placing a small object such as a ball bearing or a small metal block on top of a beaker full of fine sand: stick the beaker to the plate with some double-sided tape or some adhesive putty. As the shake table vibrates and the sand liquefies, the object will sink into it, and will become stuck in position once the vibration stops. You may need to try out a few objects and adjust the vibration frequency until you get the best effect.

The shake table kit is essentially a metal vibration plate and an adjustable 'vibration generator', which needs to be connected to a low voltage supply set at 6V DC. Do not run this continuously for more than a minute or so, as the coil becomes hot.

Set up the table before students use it, so that the metal plate rests on the felt, on the base. The magnet should be just inside the coil. Adjust the position of the magnet so that it moves in and out of the coil easily, then adjust the tension in the elastic cords so that the amplitude is about 0.5 cm when the plate vibrates. (If the cords are too loose the magnet may not return when it comes out of the coil.)

## Resources needed

Each group will need:

• SEP shake table
• Low voltage power supply (set at 6V DC)
• Straws or craft straws or wooden splints (Do not use straws with a flexible joint).
• Modelling clay – to provide a base for the straws and to provide a small load on each straw
• Activity: How earthquakes affect buildings
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