Identify the Problem
Create a bridge that can withstand the most weight yet be as efficient as possible.
Generate ideas
Constraints
- Deck elevation – 12 Meters
- No pier, no arches, no cables
- Medium concrete
- Standard load
- Carbon Steel
- Solid Bar
- 140mm x 140mm
- Only use of Balsa wood and Elmers Glue
- Each person builds half the bridge
- There has to be room for the testing device to go through your bridge
- only two cars to get across to chose from
- only use manila paper for the road surface
Criteria
- Weight
- Cost
- Strength
- Complexity
- Flexibility
- Time to build
Research
- Before building a bridge, you need to survey the area to decide the type of bridge needed.
- Beam Bridge: Are built from horizontal beams that rest on two large pillars on either end of the bridge. Uses prestressed concrete with steel rods on the inside.
- Suspension Bridge: High towers with cables holding the bridge up.
- Bridges can be built being natural disaster resistant by being built ins segments. This allows the segments to move freely and prevent the bridge from snapping.
- Bridges cost about $84 per square foot.
- Bridges are built to give about 30 years of service.
- Truss Bridge: Are built out of triangular units. These help support the bridge. Common truss bridges are the: Warren, Pratt, Howe, and K-truss
- Deck Truss: The bridge has support underneath the road.
- Through Truss: The bridge has support above the road.
- West point bridge has 3 colors telling you information on your bridge.
- Blue: Shows how much tension is on a certain bar
- Red: Shows how much a bar is compressed
- Magenta: Tells you if a bar is too slender.
- The strongest bridges in West Point Bridge have the least amount of color possible. They show the most white instead of blue, red, and magenta.
- Triangles are the most stable shape.
- Most truss bridges in West Point Bridge have a lot of tension and compression in the middle of the bridge.
- Tension and Compression are two forces that act on bridges. Tension is the force that is "trying to pull the bridge apart." Compression is the force "trying to crush the bridge like a spring." With too much tension the bridge will be pulled apart. Too much compression, and the bridge will buckle.
- Two other forces are Torsion and Shear Loading. Torsion is what happens when wind twists the bridge. Shear loading is when a load that is too big or too heavy goes on a bridge and causes the bridge to break.
- Bridges can break because of Construction accidents, Manufacturing defects, and design defect. While building our bridge, slight imperfections could weaken the bridge causing it to not perform at its best. Also each piece of balsa wood is different, making them each have different strong and weak points. This could cause the bridge to not be as strong because of the different pieces holding it together. And finally, if our design is defective, then it may not perform nearly as well as expected. While West Point Bridge is a good indicator of how strong a bridge is, it can't tell us everything we need to know. So even if our bridge worked on West Point bridge, that doesn't mean it will succeed in real life.
- My groups bridge is a warren through truss with two layers. The extra layer is for more support since we noticed one layer of triangles shows too much red color of compression on the bars. We also added the top layer to lessen the intensity of the colors in the middle. And since one layer of triangles is flimsy, the second layer makes it less flimsy. Since triangles are the strongest shape, we designed our bridge with them in hope of building a strong bridge.
References
http://www.pbs.org/wgbh/buildingbig/bridge/basics.html
http://www.wired.com/2010/07/gallery-bay-bridge/all/
http://www.virginiadot.org/business/gasb34-structure.asp
http://www.msnbc.com/rachel-maddow-show/common-types-truss-bridges
http://science.howstuffworks.com/engineering/structural/10-reasons-why-bridges-collapse.htm#page=8
http://science.howstuffworks.com/engineering/civil/bridge2.htm
http://www.wired.com/2010/07/gallery-bay-bridge/all/
http://www.virginiadot.org/business/gasb34-structure.asp
http://www.msnbc.com/rachel-maddow-show/common-types-truss-bridges
http://science.howstuffworks.com/engineering/structural/10-reasons-why-bridges-collapse.htm#page=8
http://science.howstuffworks.com/engineering/civil/bridge2.htm
Matrix
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Possible Solutions
Bridge 1 and Bridge 2 are our best designs. They both had the most amount of points from the matrix.
Bridge 1 was the cheapest and the lightest. Also it was the least complex, which led to it being able to be built fast. However it was the weakest and bent a lot when the truck rolled over it in West Point Bridge.
Bridge 2 had the most points from the matrix. It didn't stand out in any specific categories except for Complexity and Time. It was our most cost efficient bridge because for the price it was our strongest design.
Bridge 2 was our best design although it wasn't the cheapest. We picked it because out of all of our bridges, it wasn't very complex and was one of the strongest bridges.
Bridge 1 was the cheapest and the lightest. Also it was the least complex, which led to it being able to be built fast. However it was the weakest and bent a lot when the truck rolled over it in West Point Bridge.
Bridge 2 had the most points from the matrix. It didn't stand out in any specific categories except for Complexity and Time. It was our most cost efficient bridge because for the price it was our strongest design.
Bridge 2 was our best design although it wasn't the cheapest. We picked it because out of all of our bridges, it wasn't very complex and was one of the strongest bridges.
Reflection
After choosing our best solution, Bridge 2, we will now start to construct it. We will build it out of balsa wood and Elmer's glue. We found it hard to build cheap successful bridges in West Point Bridge Designer. Most of the ones that worked would have too much red or blue in a specific place. It was also hard since we were used to be able to adjust the size of the bars, now we had to only use one size. However we were able to build eight successful bridges through a trial and error process. It was hard to make a cheap bridge that will sustain the same amount of weight as a more costly bridge. After building my part of the bridge, I noticed that the bridge had warped or changed shape, and that some straight pieces of balsa were now curved. I hope that this won't greatly affect my bridges performance.
Data Analyzation/Mathematical Model
After looking through the results of our bridge testing data, we noticed that there were relationships between certain characteristics of the bridges. The average weight of all the bridges was 17.4 grams, while the average cost of all the bridges in West Point Bridge was $442,839.95. A good portion of the bridges built were deck truss bridges. Those bridges tended to break on the support structure underneath. The through truss bridges tended to break on the road or the road support structure. We noticed that the bridge cost in West Point Bridge had little effect on how much it weighed in real life. Sometimes a bridge that costs more in West Point Bridge weighed less than a cheaper bridge. For example, a groups bridge weighed 21.5 grams, but costs $273,467.67. But a other groups project weighed 14.5 grams, but costs $446,618.52. Thats a 5 gram difference. This could have been like that because one group used more glue and paper, which added extra weight to the bridge. We noticed while we were testing that the side with the worse build quality broke first, then the other side broke shortly after. Sometimes the bridge would start to cave in instead of the the sides breaking.
What Would I Change
My bridge worked very well except for the road system and support. The road was torn off the main structure of the bridge. I think that we should make the road structure more strong and in a better place so the bridge will be able to last longer.