Building a spaghetti bridge is an educational experiment that demonstrates how bridges work. 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.
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.
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).
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.
Cover the graph paper with a sheet of clear cling film. This allows you to see your template as your build your bridge, without getting glue on the graph paper.
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. Make sure the students are careful with the hot glue.
Glue all the components of your bridge together (supports, deck, and trusses).
Gradually add weight to your bridge in small increments to determine how much weight it can hold before it breaks.
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 centre (usually triangular) portion, because the top and bottom are subject to the most compression and tension, respectively.
Don't cook the spaghetti. Be careful with the hot glue.