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| 20110921 Bridge Breaking |
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We tested by placing the dowel halfway along the bridge so it runs across the center span. We used chain to hang the bucket off the dowel, and slowly add more and more sand to the bucket until the bridge breaks. The bucket is then weighed, and structural efficiency determined. Divide the load the bridge held by the weight of the bridge. The higher the load/weight ratio, the stronger the bridge! A good design spreads the force over a greater area, or moves the force from an area of weakness to an area of strength. Triangles are a strong shape that transfer the load from just one point to a much wider area. A bridge will buckle when the force of compression is greater than its ability to handle being shortened. A bridge will snap when the force of tension overcomes its ability to handle stretching.
