Double Helix members at the CSIRO Lab in Perth learnt some very important spaghetti bridge making skills thanks to Engineers Australia. Now it's your turn to have a go!
Caution: Hot glue can burn! Younger readers should make sure they have adult supervision while using a hot glue gun. For extra protection wear cotton gloves – these can be purchased from a pharmacy. You can always use craft glue but this takes much longer to dry.
You will need
a pack of spaghetti
hot glue gun and glue sticks (or craft glue)
sand (or other weight to test your bridge)
dowel, metal rod or thick stick
2 tables or boxes
What to do
You will be building a bridge that:
weighs less than 250g
spans a gap of 500mm and is 600mm long
is less than 100mm wide
We'd recommend drawing a plan of your bridge on paper first. Use your imagination; the bridge can be any shape you like as long as it is the right weight, width and length. (Hint: triangles are a strong shape!)
Build your bridge out of spaghetti and glue. The glue can only be used on overlaps, intersections and joints.
Check it weighs less than 250g and record the actual weight.
Measure your bridge to make sure it is the correct length (at least 600mm) and width (less than 100mm).
Now it's testing time! Place the bridge between two tables or boxes 500 mm apart.
Place the dowel or metal rod halfway along the bridge so it runs across the centre of the bridge.
Use string to hang the bucket off the dowel or metal rod.
Slowly add more and more sand to the bucket until the bridge breaks.
Weigh the sand, dowel and bucket your bridge held. This is the load.
Divide the load by the weight of the bridge. This is your load/weight ratio. The higher the load/weight ratio, the stronger your bridge.
Taryn and Jasmine made a bridge weighing 75g that held 675g. This means the load/weight ratio was 9. The winning bridge at the Perth Double Helix event held 4kg of sand!
Why not compare a few designs you've made, or have a competition with your friends?
There are lots of things to think about when designing a bridge, even if it is just made out of spaghetti.
The two most important forces you have to consider are compression and tension. Compression is a force that will try to compress or shorten the thing it is acting on. Tension is a force that will try to lengthen or expand the thing it is acting on. These two forces act on all bridges, big or small, and a bridge needs to be able to handle these forces without buckling or snapping.
A bridge will buckle when the force of compression is greater than the bridge's ability to handle compression. A bridge will snap when the force of tension overcomes an object's ability to handle tension.
A good bridge design will attempt to spread the force over a greater area, or move the force from an area of weakness to an area of strength.
Triangles are a strong shape. Using triangles in your bridge can help you to create both a very rigid structure and one that transfers the load from just one point to a much wider area.
The way you connect your spaghetti is also important. Where parts come together there are stress concentrations that can destroy your bridge. You may wish to glue little triangles of parts of spaghetti around the joints to make what is called a ‘gusset plate'.
Bridges are a part of everyday life. They can help us get over obstacles like rivers, roads or valleys. The Sydney Harbour Bridge, for example, is a very famous Australian icon which helps Sydneysiders cross Sydney Harbour.
Bridges are designed and constructed by civil engineers. Civil engineers work on things built in or on the ground. As well as bridges, this can include railways, harbours, road systems, dams, tunnels, power projects, and more.
There are three main types of bridges; the beam bridge, the arch bridge and the suspension bridge.
The beam bridge is the most simple. It is a horizontal beam supported at both ends. Even a log that has fallen over a stream is a beam bridge. Although they are cheap and easy to construct, they are only good for short distances.
Arch bridges, like the Sydney Harbour Bridge, are better for longer distances. The weight is carried out and down to the ground along the two curving paths that make up the arch. They can withstand large compressive forces and are made of relatively simple materials.
Suspension bridges are good if you need great length and flexibility. They consist of a main deck supported by cables which lead to towers. The weight from the deck is trasferred to the cables, then to the towers and finally down to the ground. They are good at covering distances from 500 meters to 1 kilometre.