Final Post
Our original design was based around the concept of the equilateral triangle. The equilateral triangle, we felt, would be the strongest against both tension and compression forces. We took steps to create equilateral triangles of two sizes, one size for the upper structure and another for the lower tier. This design is common, thereby effective. We followed the train of thought from the beginning that this contest would be one won largely by craftsmanship, so we hypothesized that even with an ordinary design we would be able to create an effective bridge by creating very strong joints and connections. Following this philosophy, our equilateral triangles were cut so that they would fit tightly together. These joints were then secured by flat planks on each side, creating very strong individual pieces. We then got to the step of assembling the bridge itself. Our final bridge was extremely different from what we had originally designed. We noticed that layered road beds were being used, so we decided to do the same. Our bed was different however in that instead of having three solid layers of wood, we had the road itself, a layer of sticks, and then another layer of solid wood. We did this because the solid wood design does not have much room to move, and that lack of space in our opinion would result in inflexibility which would make the road bed weaker. We then connected the triangles to the bed, top and bottom. They were held in place by being glued directly to the bed, and also by having larger wood planks glued to both the planks used on the triangles and the road bed. This created an extremely strong joint which would keep the triangles in place to ensure that the bridge would have to break them in order to fail. We then connected the triangles even more through the addition of laminated 3 stick thick bars which we glued down the side of the triangles. We then connected across and over the roadbed by adding small sticks which we glued to the previously mentioned bars. This created a strong cage surrounding the triangles which would prevent them from simply breaking off. This completed our bridge. We thought that the main failures in the supporting structures of the bridge would not be a result of the wood breaking, but the glue breaking. This proved to be correct, as the glue bonds which held the cage to the triangles broke off of both the upper and lower triangles. The break was clean down the center of the roadbed, with the immediately surrounding triangles being broken off. Were we to repeat this experiment, we would have possibly created as thick a roadbed as possible with alternating layers of lengthwise sticks and solid wood. It would also have been interesting to test a suspension bridge using some string of twine. A third upper support system shaped like an arrow with its ends pushing against the “cliffs” also seemed to be very successful. This project taught about the nature of forces especially in regards to force as being a vector, where it is in a certain direction. The goal of making these bridges was to learn to redirect those forces so that they are spread out. Pressure was demonstrated in how out bridge began to sag towards the end of its life, and how the build up of pressure caused some entire triangles to eventually snap and go flying off. Torque was seen in our bridge in how the center was the weakest, the junction point, where the force could most easily snap through the roadbed (which it did).This also taught a cold lesson in logistics. Our bridge was very ugly and looked simple, but it held up much better than did the normal clean cut bridge which was not made with the characteristics of glue in mind.
