For this project, we were told to create a sturdy bridge out of paper and paper clips. It needed to span a 40cm wide “river”, and also had to be able to hold a load. The aim was to build the strongest bridge, holding the heaviest load.
We were given 7 A4 sheets and 7 regular paper clips, and the bridge couldn’t touch the “water”. As well as this, it could not be fixed at either end by anything.
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We worked through many different ideas before coming up with our bridge design. These concepts included two thick rolls of paper fastened by paper clips, a triangular prism, and a corrugated ‘zig-zag’ structure. The difficult part was estimating the strength of the paper due to how thin and relatively weak it was compared to other materials, such as wood or metal.
After a degree of trial and error, we decided to go ahead with the triangular prism. This consisted of 3 sets of 2 sheets, two pointing downwards and one pointing upwards. We were first folded in half and then folded again into thirds. This created a strong triangular structure as the folded paper did not bend as easily. then when the three sets were folded, we attached them together with the paper clips at each side to stop them unraveling and also used another paper clip to hold it together in the middle. We then found this wasn’t long enough, so we decided to extend the length to 50cm.
Now for the test – would the bridge be strong enough to hold a heavy load without collapsing? A cardboard sheet was supplied as the base for the weight, and a paper cup was placed on top which popcorn kernels would be poured into. The load had to be in the centre of the bridge to ensure a consistent result between teams, and when the bridge started to sag, we would take the cup off and record our result with a weighing scales.
The Results…
In the first attempt, we started to pour the kernels in, and it was going well until the bridge started to fold itself outwards, causing the whole structure to start to collapse. While the triangular structure was strong, the problem was it had weaknesses at the ends where the paper ended at the peaks of the prisms. This meant it would start to lose shape when a load was applied. We weren’t sure what to do here as we didn’t have enough paper clips to secure it at every point. However, we came up with a solution using our 7th sheet – To hold the two outer prisms together on the top of the bridge, we cut a trousers-shaped piece of paper from the 7th sheet and slotted it in between them, which reinforced it further. Then we made a second attempt, which was much more successful. We filled our first cup and added a second one. The bridge gave way just as the second cup was filled, giving us a load of 644g.
Conclusions
For the remaining three attempts, we tried variations of our triangular prism shape, as we were confident that was it was a strong structure. We experimented by attaching the paper clips at different parts and also we discovered that folding the paper so that the open ends were in different directions lead to a much stronger structure as there were no open ends in the middle. However, despite some improvements in the structure, we learned that ultimately, while the shape was theoretically strong and consistent, we found it difficult to develop this idea with paper.We learned that although paper can be a very strong material when folded, it has inherent weaknesses and also becomes weaker the more it is manipulated. After playing around with different designs, the paper progressively became weaker and weaker, and was less able to hold a sustained load with every attempt. We had to use fresh sheets of paper several times,
We learned that an awareness of the material is important when designing different structures as each material responds differently to certain shapes and stresses. Paper was quite a strong material, and could potentially hold a load of several kilograms, but our shape was not the best for the material because of its properties. Although we didn’t get as high a result as we would have liked, we came out of the project having learned a lot about materials and how they work better for certain designs than others.
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