Instructions to Build a spaghetti bridge

Building a spaghetti bridge is an educational experiment that demonstrates how bridges work. The steps here give you the basic information you need to design and build your own spaghetti bridge. If you participate in a spaghetti bridge building contest, the contest rules are likely to specify allowable materials, the size of your bridge and how it will be judged. Success is typically determined by how many times its own weight your bridge can hold without breaking. Thus, your goal is to build a lightweight bridge that can support a heavyweight load.

Instructions

Things You'll Need:

• Raw spaghetti (a bridge three feet long requires about two pounds of pasta)
• White glue or a hot glue gun
• Rubber bands
• Graph paper
• Cellophane (clear plastic wrap)

1. Step 1

Build supports for your bridge. Bundle several strands of pasta together in the shape of a tube. Apply glue to each strand as you go. Hold each bundle together with a rubber band until the glue dries.

2. Step 2

Build a deck for your bridge (also known as the roadbed--the part of the bridge upon which the load will be placed). Two possible designs are: 1) A round bundle of unglued spaghetti (the lack of glue allows the spaghetti to shift as needed under the weight of the load), or 2) Several layers of spaghetti, with each layer consisting of pieces of spaghetti glued side by side to the width of the deck, and the resulting layers glued one atop another to form a thick stack (try 10 layers for starters).

3. Step 3

Design the trusses (also referred to as the substructure and superstructure) of your bridge to scale on a piece of graph paper. This will serve as a template for the building of your bridge. The best designs consist of a series of triangles, which are stronger than squares.

4. Step 4

Cover the graph paper with a sheet of cellophane (clear plastic wrap). This allows you to see your template as your build your bridge, without getting glue on the graph paper.

5. Step 5

Cut the spaghetti to fit the template, lay it out on the template and then glue them together using white glue or a hot glue gun.

6. Step 6

Glue all the components of your bridge together (supports, deck, and trusses).

7. Step 7

Gradually add weight to your bridge in small increments to determine how much weight it can hold before it breaks.

Tips & Warnings

• Experiment with making trusses using various triangle-based constructions. Try forming trusses based on the shapes of the letters M, W, V, and inverted V.
• A triangle that points down is more stable than one that points up.
• Bridges must withstand the forces of both compression and tension. These forces are optimally balanced when the top and bottom of the truss are made up of more material than the center (usually triangular) portion, because the top and bottom are subject to the most compression and tension, respectively.
• Don't cook the spaghetti.

http://www.ehow.com/how_4557074_build-spaghetti-bridge.html

Point Of an Engineer View

We need model experiments to test different constructions before you build the real thing. This is how engineers work. You don't want to have your bridge collapse the first time someone walks on it. The main point is that the material that you use for testing in the small scale model behaves exactly like the stuff (in this case steel) in the real bridge.

And here the spaghetti comes in. Spaghetti in a model bridge is just as strong as the steel in the big one. If you want to understand more about testing the strength of scale models read here:

Scale, Size and Mass Let's say your model is 50 times smaller than a real bridge. Now don't forget: your model is not only 50 times shorter, but also 50 times less wide and 50 times less high! (You have seen the same problem with the Weigh a Dinosaur experiments.) Now suppose you want the real bridge to carry 20 trucks weighing 10,000 kg each. Your model must then be able to carry a load that weighs 50 x 50 x 50 = 125,000 times less! Ten trucks together weigh 200,000 kg. Divide this by 125,000 and you get 0.16 kg = 160 grammes. That's how much your model must at least support before it breaks. Use different numbers for your own model.

We will have lots of fun doing the experiments and the results really surprise you. After many tries, you'll find a construction that is many times stronger than the bars just tied together. Here is a description of the experiments.

Why not try them yourself?

Spaghetti Bridge Experiment

We want the make a clever construction that is stronger than a single piece of spaghetti (or, a steel bar in the real thing). First, we need to know how much load a single one can carry before it breaks, and then compare it with our construction.

We test the spaghetti pieces like this. Rest the piece on two supports and tie a weight to its centre (see picture). Have several weights ready with various masses, for example 10, 20, 50, 100, 250, 500 grammes etc., whatever you can find. Start with 10 g and with each next step increase the load by adding another weight. At each step measure how much the spaghetti bar has bent. The photos and the film make it clear how this is done. Put your measurements down in a table.

Carry on adding mass until the piece breaks. Now you know how strong one spaghetti piece is. If you want to do a really good job measure a few more pieces of spaghetti, to see if some are stronger or weaker than others. Make a note of the load that an average piece can support, for instance 12.7 grammes.

Experiment also with the distance between the supports. If they are too far apart the piece will bend and slip off before it breaks. But you will find that out soon enough.

If you set the supports closer you will find that the spaghetti can carry heavier loads. Make several tests with the supports, say, 15, 12, 9 and 6 cm apart. You will need these later when you compare the strength of your construction with the strengths of the single pieces.

Make some final tests with a bundle of spaghetti, e.g. five or ten. Find out that together they are indeed five or ten times stronger than a single one. Check also what happens if you glue them together. Are they now stronger or weaker?

Constructions

Let's have a look at real steel constructions, for instance railway bridges or crane arms. You will see they all are somehow put together as series of triangles.

Try out different constructions by glueing together a few spaghetti. The best way to do this is to use a glue gun (see photo). This is an electric gun, which melts bars of plastic. When you apply it, the hot glue cools quickly and immediately binds two pieces together. No waiting.

Now find out why triangles are such clever things to build bridges and cranes with.

First, cut a number of spaghetti exactly the same length. You will need lots and lots of them. So, start making 50 pieces 5 cm long and 25 pieces 7 cm long. Or, if you plan to make a bigger bridge, 10 and 14 cm, respectively.

Glue four 5-cm long pieces together to make a square. Make another square, now with a 7-cm long piece connecting opposite corners. Test both constructions by squeezing them in the direction of the arrows. You see that the square built of two triangles is much stronger. It doesn't even make much difference whether you press in the direction of the red or the green arrows.

Now for the real thing. If you connect a number of triangles you can make a beam that is strong and light at the same time. Like this:

Let's try out different constructions. There are different ways to make a bridge from a series of connected triangles. Here you see several examples, which we called, M-, W-, V- and inverted-V-constructions:

A W-construction.

A V-construction.

An inverted-V-construction.

For our bridge we also need something to walk on, a bridge deck. We tested a bundle of 10 whole spaghetti pieces and also 10 pieces glued together.

The bundle bends and the pieces start breaking one after the other.

The ten that weren’t glued rearranged themselves and formed a round bundle that could carry a load of 400 grams. Yet, the spaghetti glued together were only able to carry a load of 300 grams. Probably the outer 2 spaghetti pieces carried the heaviest part of the load and collapsed relatively fast. The load was so great that the spaghetti started to bend:

We found out that the best construction was the “M-construction”. This beam could carry the heaviest load of all our constructions: up to 400 grams! The construction took 17 spaghetti pieces. Now, 17 times the strength of one spaghetti would only be able to carry 160 grams of load. So, our construction is 2.5 times stronger than just the pieces it was made of! This was much better than we had expected.

We wanted to test a model of a bridge that you can walk on. So we created a simple bridge with two “M-constructions” with decks on top and at the bottom each of 10 bars glued together. For this bridge we used 28 whole spaghetti bars that separately would be able to carry around 0.64 kg. Some testing with the construction gave us 2.75 kg for the maximum load. This was more that the 2 x 0.64 = 1.30 kg we had expected.

The bridge that Arie and Marc finally tested.

Here you can see a film of one of the tests we did:

Click the picture to play the movie!

Now it is up to you! We are sure that you can create a bridge that can carry an even heavier load. Try making it lighter yet stronger than our bridge. You can start a contest with your friends or class mates.

Some tips:

• 

  It makes a difference: apex up ur down!
  a triangle with the apex down is more stable than one with the apex on top (figure)

• you can use sheets of lasagne for the bridge deck

• 

  An arc bridge. Make your own bridge design and test its strength.
  try different designs (see figure). Some may be stronger than the straight beam structure. Use your imagination.

Thanks to Arie van Scheepen and Marc Luitjens

Copernicus : http://www.journal-for-young-scientists.net

Teacher Guide Patterning

The purpose of this exercise is to design and build a structure, which is capable of supporting a mass of at least 5 kg. or 11 pounds in the center of a span of 15 inches with the maximum width of roadway of 4.0 inches. The bridge design should achieve the highest efficiency possible.

The material that is to be used is #9 spaghetti (thin), which is to be supplied by the teacher. The structure must be three-dimensional and capable of fitting in the testing jig provided. Maximum points for the fabrication portion of the grade will be awarded for the lightest structure that will support the load. Bridges failing will be graded on the bridge’s structural efficiency (E). E=Max load supported/mass of the bridge.

Students will work in groups of no more than three and all in the group will receive the same grade (unless the group evaluates a member differently.) It is expected that the work will be shared equally.

In addition to the fabrication of the structure, each person will submit a one to two page report that will include all design drawings and calculations.

Students will also research bridge designs on the Internet and find one that fits their needs for the contest.

A bridge building program will also be used to construct and evaluate compression and tension members of the bridge design. The bridge building program will help students with efficiency evaluations.

Research:

Students can use books, magazines, and the library, to research bridge designs. The Internet will be used to find a web site that explains and demonstrates bridge styles and construction.

The students should include this information in printed form and attach to their report.

Bridge Building Program:

Student will make a drawing of the style of bridge they have selected.

The program will show compression and tension members and how strong they are.

A cost analysis and efficiency rating will be used to help students design and build their spaghetti bride.

Auto CAD Drawings:

A 3-D inventor drawing of each individual member, assembly, balloon drawing and presentation file, of the whole bridge.

The front elevation and side elevation of the 3-D drawing will be printed out and used as a pattern for the spaghetti bridge. The spaghetti can be cut exactly to the right size by laying it down on the drawing and cutting it.

Details about construction of the bridge:

Only spaghetti may be used for construction of the bridge. Any adhesive may be used to join the ends of the spaghetti. Longitudinal gluing may not be allowed.

No part of the bridge may extend more than ¾” below the support elevation.

The bridge length must be 15 long.

A hole must be provided in the center of the bridge to allow for the threaded rod. It is suggested that this area be strengthened to accommodate the point load.

The jig will be weighed and included in the weight on the bride. The bridge cannot weigh more that 100 grams.

Width of the bridge is 2.5 to 4.0 inches

No height requirement of total ht.

Max roadway thickness 1 inch.

Testing Procedures:

The bridge will be centered on the supports.

A bucket will be attached to the center support and the load will be applied. The student will add sand to the bucket until failure occurs. Maximum time for loading will be 5 minutes.

The weight of the filled bucket will be massed and used in the efficiency formula.

Failure of the bridge is defined as the inability of the bridge to carry additional load without breakage or sagging more that 1 cm below support elevation.

The Report:

The reports must have an introduction explaining the project.

It should have a procedure or step by step process how the bridge was constructed, materials used, and technique for construction.

It should include all calculations, formulas used, and math work.

All drawings, which included 3D and Bridge building program.

A graph of your efficiency rating.

Evaluation results and improvements made to design.

Conclusion explaining things learned during the whole process.

Bibliography page.

Title page.

Grading:

Research information (10 points) Individual

Accuracy Bridge/drawings (15 points) Individual

3-D Drawing Inventor (50 points) Individual

Building Program Drawing (20 points) Individual

Efficiency graph (10 points) Individual

Efficiency rating (50 points) Team

Report (35 points) Individual

Team Grades each persons work (10 points) Individual

Total points possible (200 points)

Time line (approx):

Research (1 day)

Bridge Building Program (4 days)

3-D Drawing (2 days)

Construction of Bridge (5 days)

Report (on own time)

Graphs and other (1 day)

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