What Type of Bridge Supports More Weight in an Earthquake
picture of the student researcher

Researched by Carmelle S.


The purpose of this experiment was to determine which type of bridge would carry more weight in a simulated earthquake.

I became interested in this idea when I saw many bridges collapse on TV during some severe earthquakes. A large sum of money was needed to rebuild the bridges. Even worse, several people died.

The information gained from this experiment would tell construction workers and engineers which kind of bridge to build in earthquake areas. This would make living in earthquake zones safer.


My hypothesis was that the suspension bridge would hold more weight than the other bridges during a simulated earthquake.

I base my hypothesis on information I found about the Golden Gate Suspension Bridge. On the web site, http://www.exploratorium.edu/faulttime/engineering/retrofit.html, it is stated that the Golden Gate Bridge was strong enough to stand an earthquake magnitude of 8.3. So suspension bridges might be the strongest type of bridge.

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The constants in this study were:

  •  The length and the width of the bridges 
  • The materials used to make the bridges
  • The surface on which the bridges are being tested 
  • The spans of all the bridges
  • The test method including the simulated earthquake

The manipulated variable was the type of bridge being tested in the simulated earthquake.

The responding variable was how much weight they could hold during the earthquake. 

To measure the responding variable I used a measuring scale. I measured how much weight the bridge held in kilograms.

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5 Strips of balsa wood (91 cm)
1 Roll of nylon twine string
1 Measuring tape (in cm)
1 Bottle of wood glue
1 Strip of pine wood 
1 Screw driver 
1 Pine boards (63 cm long, 5 cm wide)
1 Board of plywood(4-mm thick)
4 Giant rubber bands
4 Nails
8 Screws
4 Metal brackets
1 Piece of Thick rope (30 cm long)
1 Weighing scale 
1  A large bucket
Variable Weights

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Making the Bridges
1. Obtain all materials listed.
Beam Bridges
2. Take one board of the balsa wood. Saw two 45.5 cm long pieces.
3. Take the strip of pinewood and cut two 10 cm long pieces. 
4. Take one strip of the 45.5 cm long balsa wood and two pieces of the-10 cm tall pinewood and glue two pieces of the pinewood, each one 7 cm from the end of the balsa wood.
5. Repeat #2-4 until you have three beam bridges. Place them aside.
See appendix for details
Suspension and Cable Stayed Bridges
6. For the suspension and cable stayed bridges, repeat step #2-4 six times.
7. On each bridge, glue two more pieces pinewood to the other side of the balsa wood, each being 7 cm from the end. Let the glue dry.
8. Cut two pieces of sting, each being 115 cm in length. Tie the ends together and fit over one bridge so it would look more like a suspension bridge.
9. Then, cut four 20 cm long pieces of string. Tie them along the over one hanging string. 
10. Then, bring the strings ends under the wooden beam and tie the ends to the other overhanging piece of string.
11. Repeat steps #8-10 two more times. Now you have three suspension bridges.
12. Punch two small holes on either side of the balsa wood with a screwdriver. Each hole must be 8.5 cm in from the posts.
13. Cut two pieces of 130 cm sting.
14.  Run one piece of string over the post down through the holes on the left and over the other post.
15. Bring the rest of the string under the wood to the other end of the string. Tie the string securely together. 
16. Repeat steps #14-15 one more time except run the sting through the right holes.
17. Repeat steps #12-16 until you get three cable-stayed bridges. 
Making the Earthquake Simulator
18. Saw two pieces of 100 cm pinewood and two pieces 50 cm. 
19. Make a fence with the pinewood. Hammer nails and screw screws into the corners of the fence. 
20. Attach one metal bracket to each corner of the fence with two screws on each bracket.
21. Drill four holes into the corners of the plywood. Saw a 20 cm in diameter circle into the middle of the plywood. 
22. Put one rubber band through the holes and lope over the corners of the fence.

How to do the experiment
23. Take the earthquake simulator and suspend it between two chairs or tables.
24. Take one bridge and drill piers to the plywood. Just drill so that the bridge stays on the bridge.
25. Tie the rope around the middle of the bridge being tested and tie onto the bucket handle.
26. Make sure that the rope is tied on securely. Start adding the weights. Shake the earthquake while adding the weights.
27. Stop adding weights to the bucket when the bridge starts to break. 
28. Once broken, take the bucket and weigh on a weighing scale. Record data.

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The original purpose of this experiment was to determine which type of bridge would carry more weight in a simulated earthquake.

The results of the experiment were the average amount the beam bridges held during an earthquake was 10.3421 kg. The average amount the cable stayed bridges held was 11.189 kg and the average amount the suspension bridge held was 15.2714 kg.



My hypothesis was that the suspension bridge would hold more weight than the other bridges during a simulated earthquake.

The results indicate that this hypothesis should be accepted. The suspension bridges held more weight than the other bridges. 

Because of the results of this experiment, I wonder how much weight could a concrete arch and an iron arch could carry during an earthquake. 

If I were to conduct this project again I would have used a more accurate weighing scale, used a wider variety of bridge types, and I would try to have a better project log. 

Research Report

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Baxter, Nicola.  Bridges. Franklin Watts, 2000.  P 6-21

"Bridge Structure." World Book Encyclopedia. 2001

Cooper, Barbara. How Bridges Are Made. New York: New York, 1985.
 P.4-5, 28-30

"Earthquakes." Basic Movements.11/28/01 http://www.thetech.org/exibits_events/noyce_center/topics/3le.html

Grade 7 Natural Disasters Project "Earthquakes" Earthquakes. 11/28/01 http://www.germantown.k12.il.us/html/earthquakes.html

" Life Along the Fault line."  Building For the Big One. 11/7/01 http://www.exploratorium.edu/faulttime/engineering/retrofit.html

McGrath, Kimberly. World of Invention Second Edition,

Singer, Donna. Structures. Stek-Vaughn Company, 1995 p. 38-39

Videon, Fred. "Bridge." The World Book Encyclopedia. 1999. P.600-603 


 I would like to thank the following people. Without their help my project would not have been possible.
* My mom for buying my project board, letting me stay after school to work, and for transporting me to early classes SOAR.
* My dad for helping me build my earthquake simulator and for cutting my wood.
* Mrs. Helms for helping me cut my papers for my board and for helping me in some parts of the project.
* Mrs. Hostetler for pointing out the mistakes that I needed to fix. 
* Mr. Newkirk for providing me with the supplies I needed to help me with my project, for providing some equipment that I needed. 

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