For my Urban Planning course, we were assigned to build a functional bridge using Popsicle sticks, test our bridge against increasing loads, and analyze the results of the tests. In this unit we learned about the law of sines and cosines, vectors, and Newton's laws of motion. The purpose of this action project was to build a functional truss bridge that can sustain dynamic loads. I’m proud of the work I put into the bridge. I learned about the different types of bridges, such as the truss bridge and suspension bridge.
We were inspired by the Pratt Truss bridge design, which is a subcategory of a truss bridge. “A truss bridge is a bridge whose load-bearing superstructure is composed of a truss, a structure of connected elements forming triangular units” (WIKIPEDIA). The connected elements may experience stress from tension (the pulling force exerted by each end of a string/rod/cable etc) or/and compression (the pushing forces to different points on a structure or material).
The Standard Pratt Truss design uses right triangles, specifically with 90-45-45 degree angles. The Pratt Truss bridge is similar to the bridge below (90-45-45 degree angles):
After finding out that every group would be using equal amounts of materials to build a bridge, my teammate and I researched specific bridge designs already in use and common problems associated with bridges. Then, we drafted an accurate and well-thought-out plan before we started building our bridge. We decided to build a Pratt bridge because it had the most triangles. Triangles are the strongest geometrical shape because they spread the weight load to each of the sides. We started by putting the triangular truss system sides of the bridge together, then attaching the triangular truss system beam across so that we had the base. It was difficult to glue all the pieces together and the drying period was extremely long. We used clamps to hold the different pieces and glued them together. Our last step was attaching a few more Popsicle sticks across the trusses to add stability.
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| GN, Tension and compression diagram 2015. |
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| TC, Bridge 2015. |
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| TC, The blueprint of the Bridge 2015. |
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| TC, Bridge 2015. |
All of our Popsicle sticks were 4.5 inches long, and all of our triangles were 90-45-45 degree angles. “A Pratt truss is a simple truss structure with vertical compression (pushing together) members and diagonal tension (pulling apart) members” (The Balsawood Bridge). Our scale is 1 inch on the drawing = 3.5 inches in real life. The length of the blueprint bridge is 4 inches across (3.5 X 4 = 14 inches in real life). Our bridge was 5 inches tall and 4.5 inches wide.
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