There are 4 major types of bridges, each with their own strengths and weaknesses when made out of spaghetti:

The Beam is the simplest type of bridge, and it basically a plank held up by two or more supports connected to the base of the bridge.

While this is clearly the easiest type of bridge to build, due to its simplicity, I don’t think it is the best design when made out of spaghetti. This is because it requires a strong, rigid ‘plank’ spanning the length of the bridge that can hold great loads. When made out of reinforced concrete and steel girders this is not a problem, it is for spaghetti, however, that breaks easily under compression. Because of this we decided to rule this bridge out of our design

The second major type of bridge is the Arch. This design has been around centuries, being used to made archways in castles etc. Because of its history it is known as a notoriously strong design that has stood the test of time. When a load is placed in the middle, it works by dissipating the weight onto adjacent blocks (in arches) down towards the base. This allows surprisingly large loads to be applied before it breaks, as it evenly spreads out he weight allowing each part of the bridge to work together and remain strong. The reason we decided to avoid an arch bridge is due to the curvature of the bottom side of the bridge.
 There were three possible ways to form this semi-circle out of pasta:
•	The first is by forming the pasta around a template, clamping it down and then gluing. While this would create a nice, round shape, it would require a lot of glue to hold the pasta in place as it all wants to straighten out. This was made especially difficult as the rules stated that only joins between pasta could be glued (which we read as the ends of two pieces) so we wouldn’t be able to glue down the length of the pastas to hold them together. As our final goal is to build a bridge that has the best load to mass ration, we decided not to build this bridge, as it would require vast quantities of glue that would decrease out load/mass ratio.
•	The second way to form the pasta into the semi-circle shape was to cook it, shape it, and then dry it out. We feared that dehydrating the pasta could cause it to become brittle, and as such would be a monumental fail when it came to testing the bridge.
•	The last way to create the bottom was to form it out of small increments of straight pasta to give the rounded affect. This would lead to many joins within the bridge, increasing the chance of failure of one of them.
Because of this we decided not to build this bridge

The cable-stayed bridge requires a strong, rigid anchor that supports the roadway. Because of this it is best suited for rivers where an anchor support spot is available to greatly increase the strength of the bridge. It is also suitable in small valleys, where supports can be places further into the valley. The supporting cables would be strong when made out of spaghetti, as it is surprisingly strong when under tension. The centre pillar could be made of multiple strands to increase strength and provide a rigid design. Because of this it would be great design…. If the bridge wasn’t high up on a desk so a support column could be dropped down onto the ground. Without this column a large amount of stress is placed onto each end of the bridge that is connected to desk, as the effective torque arm increases.  This would that when a load was placed in the centre, there would be little support, and it would collapse easily. Because of this we decided not to build a cable-stayed bridge.

The bridge we did decide to build was the truss bridge. This was due to the relative simplicity and strength of the design. All the parts of the bridge were made out of straight sections that could be easily fabricated out of spaghetti. Each part of it was also made out of large lengths of spaghetti. This minimized the amount of glue joins between strands, cutting down on the weight and the possibility of weak joins. The load bearing lengths could simply be made out of multiple strands of spaghetti to strengthen them. The bridge can be made to easily join our 40cm gap, by simply adding or taking away one of the square sections, or by simply altering their width/height. The bridge also allows for a simple roadway to be laid to comply to the rules of the investigation.