The Blog

Nov 25

Detailed list of materials-

Materials below are all foam board, the materials did have some cut outs for joints but required the measurements to allow these cut out to be made

Six 801×51 millimetres (main legs)

Two 441×51 millimetres (top beam)

Two 180×51 millimetres (top strut)

Two 250×51 millimetres (top-middle strut)

Two 330×51 millimetres (middle-bottom strut)

Two 400×51 millimetres (bottom strut)

Three 800×51 millimetres (middle beam)

Three 200×51 millimetres (supporting struts)

 

List of structural components-

Diagonal legs (outside legs)/weight bearing & span gap/high importance

Diagonal legs (middle leg)/weight bearing & span gap/low importance

Top beam structure (rectangle structure)/resisting buckling/medium importance

Weight platform and support structure/weight support/high importance

Cross struts (on legs)/support leg structure & direction/medium importance

 

While working on the bridge it was clear we needed to find a solution which could be strong but also minimalistic. This meant making a good weight bearing structure with as little materials as possible. Our bridge paced third in the ranking compared to the other bridges within the class, but out of the top three bridges we used the least materials.

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Although the bridge held a reasonable load of 4.4 kilograms there were some obvious problems with the structure. One of the blatant problems was that the centre leg of the bridge wasn’t able to reach the side platforms at all, on either side. This makes the leg completely useless and a waste of material. This section of the bridge needed to be removed and redesign and then re-cut with more consideration on the measurement of the leg and the angle it requires to be at.

imageThe next problem with the structure was that the outer legs that were angle outwards were only just able to reach the side platforms, but it required a weight to be on the bridge. Although the bridge held 4.4 kilograms it required a kilogram to reach each side only allowing 3.4 kilograms to be added. The angle of the outer legs needs to be considered highly, not just how high the legs are elevated but also how much they span away from the centre of the structure.

Besides the initial problems with the design and manufacture of the project it held well, until the legs began to buckle mainly where the joints were. Once the structure began to buckle it only took a very small addition in weight to make it fully collapse. The material used was quite durable up to a point.imageimage There are a number of ways that his problem could be resolved such as: making the legs twice a thick, using twice as many legs but have two exactly side by side. The amount of legs can also be increased, a reasonable amount would be five although any amount can be used but it would affect the width the bridge would need to be and would require a lot more material. Another possible way to increase the legs would be to add legs at the first or second strut; this would mean they wouldn’t be the full length like other legs thereby using less material. If the width of the legs was made greater up to ten millimetres thicker this would make their strength greater. The length of the legs can also be decreased, the shorter the leg the stronger it will be, but this mean horizontal beams and struts would need to be stronger. imageThere is also the possibility of using some of the other material which wasn’t present within our project such as the string or tape. The string can be used as a structural component to stop the bridge going to either side and/or the tape can be used to strengthen joints. There was also the problem of the legs having the joint and the struts not. This either needs to be the other way around or both need joints. If both have joints then the other piece will strengthen the joint. If only the struts have joint this will make the legs much stronger but will cause the struts to be a lot weaker. Another way to strengthen struts and legs is to have a structural component that runs the length of the bridge and not just the width. This will make the bridge more rigid and if a component is placed on both sides of the legs it will make them three times as thick.

Our bridge was one of the highest; this meant that gravity would have a larger effect on the strain. There are two possible solutions for this: either makes the entire bridge lower, this would mean redesigning every section of the bridge or the weight can be lowered and would only mean an addition would be required to replace the current weight platform.image

The legs didn’t have enough support along the bottom of them. Although there were struts the bottom of the legs was where the weight affected the bridge most as it was where the contact points were. The physics of the bridge needed to be considered more. It is logical that the contact points would be more strained and so the design needed to reflect this but didn’t. The struts spacing needs to vary to reflect this physics and practicality of the structure. Adding more struts to the lower section of the legs would be reasonable, possibly even in contact with the surface to increase the contact point thereby spreading the load more.

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The friction between the legs and struts seemed to work well but this method made the legs weaker. The struts purpose was to give the impression of shorter legs as shorter components are stronger. The struts were also required though to make sure that the legs wouldn’t just keep spreading outwards and cause the bridge to keep lowering. By moving the struts underneath this would mean the weight of the struts wouldn’t act through the legs so much but would still stop the legs going outwards. The only problem is that the friction may not be great enough to hold the struts up; this will mean joints need to be as tight as possible.

 

Overall the major downfall of the bridge was the lack of consideration given to the physics of the design, this meant areas of the bridge were weaker than others and even caused issues during manufacturing of the bridge.

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