Avoiding Disaster: The Right Bridge Design *
*Note: This is an abbreviated Project Idea, without notes to start your background research, a specific list of materials, or a procedure for how to do the experiment. You can identify abbreviated Project Ideas by the asterisk at the end of the title. If you want a Project Idea with full instructions, please pick one without an asterisk.
Abstract
A bridge collapse, like that of the I-35W Mississippi River Bridge shown below, can be a major disaster. Bridges that cannot hold enough weight to do their intended job can be a serious public safety issue. And if they collapse, they can also cause economic damage due to costly rebuilding and people and companies scrambling to figure out how to circumvent the months of traffic impacts.
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| Figure 1. On August 1, 2007 the I-35W Mississippi River Bridge collapsed killing 13 people and injuring 140 others. The collapse was captured in a series of photos from a nearby security camera. It was later determined by the NSTA that a design flaw was the primary reason for the bridge's collapse (U.S. Army Corps of Engineers, 2007). |
You can investigate how different bridge designs are ideal for different situations. Do some bridge designs hold more weight than others? Do they require more materials? What is the strongest bridge that can be built for the least amount of materials? Try your hand at building and testing a couple of bridges. You may be interested in creating your own bridge designs or modeling some existing designs. Or you can read more about the I-35W Mississippi River Bridge collapse, or other famous bridge collapses, and model that disaster.
For this civil engineering project, try making your bridges out of popsicle sticks or straws. The Science Buddies' The Effect of Bridge Design on Weight Bearing Capacity project idea has detailed information and tips on how to build popsicle stick and straw bridges.
Credits
Sandra Slutz, PhD, Science Buddies
- Elmer's® is a registered trademark of Elmer's Products, Inc.
- Popsicle® is a registered trademark of Good Humor-Breyers Ice Cream, which is a subsidiary of Unilever Supply Chain, Inc.
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Last edit date: 2013-02-16
Materials and Equipment 
Supplies for this project are available in one convenient kit from the Science Buddies Store
This is an engineering project, so the materials you use will depend on your engineering goals. Here are suggested materials, all of which come in the Science Buddies kit for this project:
- Graph paper, for drawing bridge schematics
- Popsicle® sticks (about 60–100 per bridge, depending on the design)
- Wire cutters, for cutting Popsicle sticks
- Elmer's® Carpenter's Wood Glue or Elmer's® Glue-All
- Cotton swabs, for applying wood glue (about 100)
- Binder clips, in both medium and small sizes, for clamping joints on Popsicle stick bridges (12 of each size per bridge; you will need more if you build more than one bridge at a time)
- Plastic straws, straight (about 20–30 per bridge, depending on the design)
- Clear tape, ½ inch width
- Gram balance for weighing bridges, such as the Fast Weigh MS-500-BLK Digital Pocket Scale, 500 by 0.1 G , available at
Amazon.com
- Masking tape
- Loading block with hook or eyebolt, for testing bridge strength
- Container for holding bridge load, such as a large bucket
- Rope, ¼ inch to ½ inch diameter (about 3 feet)
- Weights for testing bridge strength (can use metal weights, sand, or water in a container)
- Bathroom scale, for weighing how much weight it takes to break the bridge
The following equipment is optional:
- Camera for before and after photos, and/or
- Video camera for live movie of bridge testing,
- Tripod or helper for video recording.
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Frequently Asked Questions (FAQ)
If you are having trouble with this project, please read the FAQ below. You may find the answer to your question.
Q: I am trying to print the schematics from the website, but they are not printing at full size, or only half the schematic is printing. What can I do?
A: The schematics are made for 11 inch by 17 inch paper. If you are printing them on smaller paper, then the schematics will not print correctly. Depending on your printer, only part of the schematic may print, or the entire thing might be shrunk to fit on your printer's paper. Try printing the schematics on a printer that prints on 11 inch by 17 inch paper. You can find these at most copy centers. Or, check your printer's owner's manual to see if your printer can tile a larger page onto multiple, smaller pages.
Q: How long should I let the glue dry before unclamping the clamps on a Popsicle stick bridge?
A: Let the glue dry completely before removing the clamps. 8 hours of drying time is a good rule-of-thumb, but the glue may take shorter or longer to try, depending on the temperature and humidity of your workplace. When comparing bridge designs, make sure to let each bridge dry for the same amount of time.
Q: I am having a hard time finding two things that are the same height to lay my bridge across. Is it important than the supports the bridge rests on are the same height?
A: Yes, it is important that both sides supporting the bridge are the same height, otherwise the force of the load will not be symmetrically distributed across the bridge. If you are having problems finding two objects that are the same height, you can put some cardboard, books, or paper on top of the shorter object to make it as tall as the taller object.
Q: My bucket or loading container is all the way full, but the bridge has not broken. What should I do?
A: You built a strong bridge! You have a couple options. First, you could detach the bucket or loading container from the bridge and replace it with a larger bucket. Or, you could fill the bucket with a denser material. Sand, for example, is denser than water, so a bucket full of sand will weigh more than a bucket full of water, if the two buckets are the same size.
Q: How do I make this into a science project?
A: This science project (or engineering project, to be more precise) is very open-ended. Once you have built the two bridges whose designs come with the project, use the Engineering Design Project Guide [http://www.sciencebuddies.org/science-fair-projects/engineering-design-process-guide.shtml] to help you refine your goals. Think about what criteria you want your bridges to meet (how much weight to hold, a particular strength-to-weight ratio, how long the bridge can be, etc.) and then design a bridge to meet those criteria. Build and test that bridge, and use what you learn from that first bridge to improve the next one you build. Continue improving your bridge design until you meet your design criteria.
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