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Which Bridge Design Supports the Most Weight ?

Researched by Megan C. 


The purpose of this experiment was to determine whether suspension bridges or cable -stayed bridges would support the most mass.

I became interested in this idea because I want to become an architect someday and I know they build bridges and other structures that have to support lots of mass. 

The information gained from this experiment will let engineers know which bridge type supports the most mass and will let designers decide which bridge to use based on the flow of traffic the bridge is expected to support. 


My hypothesis is that a cable-stayed bridge will support more mass than a similar built suspension bridge. 

I base my hypothesis on my understanding that suspension bridges could break apart easily if any one of the cables broke. I learned this from a video clip showing the Tacoma Narrows Bridge falling apart. 


The constants in this study were:  
The materials used in construction 
The way of measuring  
How many times I test the bridges  
The way I test the bridges

The manipulated variable was the design of the bridges I use.

The responding variable was how much mass the model bridges will support. 

To measure the responding variable I will add little weights to a container attached to the bottom of the model bridges. Then I'll weigh the mass in grams. 

4 balsa wood strips 1/2 inch wide
4 wood dowels 1/2 inch wide
1 bottle of glue for models
1 roll lightweight twine
1 roll of fishing string
12 kg Small weights



1.Gather the materials needed such as balsa wood, twine, camera, basket, and weights. 
2. Assemble two bridges, which are a suspension bridge and cable-stayed for testing. 
3. Build a harness by taping some fishing string to strips of balsa wood. 
4.Take the finished bridges and attach basket to the middle of the bridges with the harness to support the mass. 
5.Takepictureswhile assembling and testing the bridges to put on the board.  
6. Pick one of the bridges to test first. 
7. Make sure nothing is missing from the bridge before you start. 
8. Fill the basket with weights one at a time.  
9. Keep adding weights to the basket until the bridge breaks.  
10. Test the second bridge the same way the other bridge was tested.  
11. Figure out which bridge design held the most mass. 
12. Take observations in experiment log. 
13. Record data in the experiment log. 
14. Start over again to test another set of two bridges. 
15. Do these procedures for four tests total.  


The original purpose of this experiment was to see which bridge design supports the most mass.  It compared two kinds of bridges: a Suspension bridge and a Cable-Stayed bridge.

The result of the experiment showed that the cable-stayed bridges by far held more mass than the suspension bridges. The first cable-stayed bridge held 10289.6 grams and the second held 6402.8 grams for an average of 8346.2 grams .The suspension bridges held 5509.4 grams and 3629.2 grams for an average of 4569.3 grams.

I observed that one suspension bridge broke immediately after one of the vertical suspension strings snapped. It should be noted that first cable-stayed bridge never broke with the full mass on it. 



My hypothesis was that a cable-stayed bridge would support more mass than a suspension bridge.

The results indicate that this hypothesis should be accepted because the cable-stayed bridge held more mass. 

Because of the results of this experiment, I wonder if using more twine would have had a different affect on the bridges

If I were to conduct this project again I would make sure that I have extra weights on hand incase I need them. I also would have taken pictures when I was assembling the bridges.  




Bridges are built to make life easier. The first bridges were made of logs, vines, stones, or bricks. Since then the materials have changed to concrete, wood, steel, blocks of stone and cables. Bridges are used to get people and vehicles safely over obstacles that cannot be crossed by foot or car.  
Designing Bridges 
   When designing a bridge, engineers take the intended load, width, and height of the span into account. Engineers build strong structured piers that are made out of concrete and steel and they support the bridge. A bridge must be able to support themselves and the mass its supporting. Designing and building a bridge is a complex task. 

Types of bridges 
    Suspension bridges are best to use across large areas because their span is longer than most bridges. The suspension bridges are light and flexible. Suspension bridges may sway in strong winds. A suspension bridge has at least two main cables. 

     Cable-stayed bridges span about 700 feet on a real cable-stayed bridge. Cable-stayed bridges have reached spans as long as 1,700 feet. Cable-stayed bridge towers are connected directly to the deck by steel cables. Cables can be extended from the towers to the roadways several different ways. Cable-stayed bridges resemble suspension bridges.

     Some bridges are built to let air and water pass through them without harming the bridge. An example of that would be the truss bridge and an open-spandrel bridge. These safety Designs could help the bridge from breaking.  


Bridges are important to our life style. If we didn’t have bridges traffic would be heavy and we couldn’t cross obstacles in cars. Not having bridges would result in a slow-moving society instead of the fast one we have today.


"Bridges", The New Book of Popular Science, 1998, volume 6, pg. 41-42 

Kingston, Jeremy and Lockwood, Arthur. How Bridges Are Made. New York: First Published by Facts on File,Inc., 

Outerbridge, David and Outerbridge, Graeme. Bridges. New York: Harry N. Abrams,INC., 

The Great East River Bridge. New York: Harry N. Abrams, INC.,, 47,50-53,

Videon, Fred F. "Bridges." World Book Encyclopedia. 1999 ed. CD-ROM 

Videon, Fred F. "Bridge."  The World Book Encyclopedia. 1995. Vol.2 pg.610-613


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