Instructions for Model Buildings

At IRIS seismology workshops, groups of 4 or 5 design and build structures and then test them on a shake table.

L. Braile

(Developed for IRIS Education and Outreach Workshops)

Materials:

bulletPosterboard
4 - 8 x 8 cm squares (floors)
12 - 1 x 10 cm strips (uprights)*
12 - 1 x 15 cm strips (reinforcing)*
bulletScotch Tape (2 cm or 3/4" wide) 80 cm length (Plan accordingly!)
bulletScissors
bullet30 cm ruler

Rules:

bulletBuilding must be:
30 cm high
at least 3 stories
bulletMaterials are limited (realistic)

Design:

bulletNote importance of shear or diagonal support. This concept can be illustrated (and explained) using the shear wall model from Seismic Sleuths. One can also build model walls using short strips (1 x 10 cm and 1 x 14.4 cm) of 1/16" thick mounting board, or other similar materials such as popsicle sticks, and magnets or mounting putty for joints. Without diagonal bracing, the model wall is relatively strong for a static, vertical load. However, a horizontal load or shaking causes the wall to collapse. With the diagonal bracing (shear-support) installed, the wall is much stronger and more resistant to shaking.
bulletSimple, rectangular building designs are effective. Many design options, particularly for the bracing, are possible.

Testing:

bulletBuildings are tested on the horizontal motion shake table. Tape the base of the building to the base plate of the shake table. We choose the direction to orient the building.
bulletAdd masses to the floors and roof of the building. Masses should be about 30 to 80 g each. Begin testing with small masses. Steel washers of 3-4 sizes make convenient and effective masses. Tape washers to floors and roof.
bulletShake building at three frequencies - low, medium and high - and at three amplitudes - low, medium and high. An accelerometer on the base plate can be used to quantify the shaking and make comparisons between the testing of different buildings more consistent. A second accelerometer can be attached to the top of the building to observe amplification and resonance effects.
bulletIn our experience, using the instructions and materials described here, it will usually be possible for most buildings to survive the shaking using small masses (30-50 g). However, few buildings with these materials will withstand strong (about 1 g), high frequency (about 10 Hz) shaking with larger masses (50-80 g). Interesting resonance and amplification effects will be visible for some frequencies and amplitudes of shaking.

 

*The widths of these strips can be varied from about 1 cm to 2 cm. It will be more difficult to design and build a "successful" building with the thinner strips. A reasonable choice for most applications is 2 cm strips for uprights and 1 cm strips for reinforcing.

Photos of the contest at the 2002 San Diego, CA, NSTA meeting.

I've also had students build water towers.