Towers - Logistics

Time
At least 2 hours to build structures and 5 minutes to test each one.

Grouping
Groups of 2-4 students.

Materials
Each group of students needs:

• 1 cardboard base (approximately 25 cm by 25 cm)
• 30 straws
• 100 paper clips (one box)
• 20 straight pins
• 2 meters of string

The class needs:

• 10-20 sandbags consisting of 250 grams sand in a sandwich sized ziplock bag. The bag should be taped into a sausage shaped cylinder for rigidity and ease of mounting onto the towers.
• 1 earthquake tower testing platform with a movable platform connected to a rigid frame by rubber bands, springs, or a motor. Several designs may be found in the Sources section.
• 4 large binder clips to secure the cardboard bases to the shake table platform.

Setting
Classroom

Towers - Background

Teacher Background
I found this to be a great end of the year project when the kids are wiggly and not able to focus anymore on bookwork. They thoroughly enjoy the competitive nature of the challenge and get very involved in designing, building and redesigning their structures.

The student handout provided gives the criteria that I assigned to my students as well as a grading rubric. Briefly, the structures must meet the following requirements:

• The building must fit on the base.
• The building must be at least 36 cm tall.
• The building must have 2 stories that are each at least 18 cm tall (approximately the height of 1 straw).
• Each story must support the weight of at least 1 sand bag (250 grams) without collapsing.
• A construction drawing with measurements and analysis must be submitted before earthquake testing.
• To survive an earthquake test, the building must not collapse for 10 seconds after the earthquake begins. The weights must stay on the building.

I observed the structure after each stage of testing described below. If at any point the structure buckled to the point that the sandbags fell off or dropped by more than halfway to the ground (a sandbag on the first story 18 cm high can fall as much as 9 cm and still be considered passing while a sandbag on the second story 36 cm off the ground can fall 18 cm) the structure was considered to have failed that stage of testing. Students had 2 minutes to repair any damage to their structure between each stage of testing although no new straws or materials could be provided.

1. Place 1 sandbag on the first story.
2. Place 1 sandbag on the second story.
3. Minor earthquake with 1 sandbag on the top story. I designated that moving the platform horizontally to the side so that it touched the frame started a minor earthquake. No vertical motion was involved.
4. Major earthquake with 1 sandbag on the top story. I designated that moving one corner of the platform so that it touched the corner of the frame as well as the table below started a major earthquake, leading to both horizontal and vertical motion.
5. Major earthquake with 1 sandbag on the top story and 1 sandbag on the first story.
6. Major earthquake with 2 sandbags on the top story and 1 sandbag on the first story.
7. Major earthquake with 2 sandbags on the top story and 2 sandbags on the first story.
8. Continue major earthquakes adding 1 sandbag at a time, first to the top story, then to the first story.

The best structure in my classes survived until a major earthquake with 4 sandbags on the top story and 3 sandbags on the first story.

Student Prerequisites
None, although the activity fits well among the seismology lessons.

Towers - Lesson Plan

Getting Ready

1. Build your earthquake shake table (See Sources section).
2. Prepare the sand bags.
3. Do a trial run with a structure of your own design to see where students may run into trouble. Securing the structure to the foundation and securing the joints are two areas where students run into trouble.

Lesson Plan

1. Introduce the project to the students.
2. Explain the rules and requirements.
3. Demonstrate the testing procedures and show how the shake table works.
4. Show students some of the different methods for joining straws together without folding the straws and compromising their integrity.
5. 2 straws may be pinned together with a straight pin.
6. A paper clip may be partly opened up – the inner U pulled out from the outer U – and each U may be slipped into a different straw.
7. Holes may be drilled with the pins and the string slipped through to tie straws together.
8. Allow students to begin designing and building.
9. Interrupt class at once or twice a class period for 5 minute “teaching commercials” based on various successful student designs or to combat problems multiple teams may have encountered. Some of the teaching commercials I included were:

• Strategies for how to secure the structure to the foundation using paper clips, pins and/or string.
• Would a better structure have a wide base of a narrow base?
• Would a better structure be symmetrical or asymmertrical?
• A description of trusses and cross-bracing and discussion of their use in bridges, earthquake retrofitting, and other structural engineering.
• How can you secure the sand bags so that they don’t fall off?

1. Test the structures. I chose to have students test their structures as they finished. This allowed for groups to work at different paces and reduced the overall number of days the students spent on this project. Another option is to require all teams to finish building on the same day so that testing could occur on the following day. In this way, all students can watch the others and make observations about the different structures, noting what worked and what didn’t.

Towers - Sources and Standards

Sources
This activity was inspired by the WGBH production of “Structures”, produced and narrated by Bebe Nixon. In this video designed to introduce teachers to inquiry-based teaching methods, students build towers and bridges out of drinking straws and see what is the maximum amount of weight each tower or bridge can hold. I adapted this lesson as a complement to the plate tectonics unit.

Shake TableTo create your own very simple earthquake table that is more like a trampoline than a standard, motor controlled earthquake table:

1. Cut a piece of board or plywood into a 12” square. If you wish, create a raised edge for your platform by nailing lengths of 1/2” square dowel on top of each of the sides.
2. Mount wood screws on the under side of the plywood at each corner and at the center of each side. Don’t screw the screws in all the way, make sure at least 1/4” sticks up so you can loop a rubber band around it.
3. Construct a frame out of 2” x 4”s that fits around the wood square with around 1/2” clearance between the outer edge of the square and the inside edge of the frame. Make sure the 2” x 4”s are oriented so that the frame is 4” high.
4. Mount wood screws on the top edge of the frame at each corner and at the center of each side. Again, don’t screw in the screws all the way.
5. Loop a rubber band around each pair of screws so that the plywood square is suspended like a trampoline within the frame.

Other earthquake table designs powered by an electric drill are described by John Lahr.

A great, very accessible resource on structural engineering principles with projects that can be adapted for the classroom is the book The Art of Construction: Projects and Principles for Beginning Engineers and Architects by Mario Salvadori, Chicago Review Press (1981).

Standards
Grade 6 – Earth Science
Plate Tectonics and Earth's Structure
1. Plate tectonics accounts for important features of Earth's surface and major geologic events. As a basis for understanding this concept:
d. Students know that earthquakes are sudden motions along breaks in the crust called faults and that volcanoes and fissures are locations where magma reaches the surface.
e. Students know major geologic events, such as earthquakes, volcanic eruptions, and mountain building, result from plate motions.

Shaping Earth's Surface
2. Topography is reshaped by the weathering of rock and soil and by the transportation and deposition of sediment. As a basis for understanding this concept:
d. Students know earthquakes, volcanic eruptions, landslides, and floods change human and wildlife habitats.