The Bridge Project:
Each group was tasked with creating a bridge that spans an 18-inch gap using only 200 popsicle sticks and Elmer's glue. Each group could not place glue on over 50% percent of each stick.
The Trusses
With our bridge, we decided to incorporate triangular trusses on the sides of the main structure of the bridge. As triangles are one of the strongest shapes in engineering, they help evenly distribute the weight to all parts of the bridge. As the main load is placed the middle of the brigde, the trusses help distribute the load to the rest of the bridge, and help carry a larger amount of weight.
Most Important Aspects
One of the most important aspects to this bridge are the main structures of overlapping sets of three popsicle sticks. These are the main supports that the trusses are built off of. They are structured vertically instead of horizontally to prevented bending and inevitable snapping, and grouped in sets of three to provide more support. Without these, or if there were less sticks in the support, the bridge would hold a very small amount of weight.
How Did the Forces Interactact with our Bridge?
The forces of the bridge did interact with our bridge by causing compression and tension in certain areas. The top section of our bridge that mainly supported the weight was under a lot of compression. The weight pressed down on the top of the bridge, causing the main support to compress. In addition to this, the trusses were also under a lot of compression, as the load presses down against the main span of the bridge, pressing down against the trusses. The bottom of the bridge is under a lot of tension, as the main load pressing on the bridge causes it to slightly bend, pulling appart the bottom section of the bridge.
Main Flaws
The Major flaw that this bridge had were the popsicle sticks holding together the main two sides were not supported enough. There were only sets of one popsicle sticks holding the main structure of the bridge together, and they easily snapped. In addition to this, they were not glued as well as they could have been, and the glue did not hold that much weight.
Why Did our Bridge Break?
Our bridge broke because of the popsicle sticks that were placed to hold together the main trusses and sides together were not supported enough, and easily snapped and popped off. Since there was only one layer of popsicle sticks, and no other sticks on top to hold them together, they easily broke. In addition to this, the glue was not strong enough to keep these sticks in place. The bridge broke because one of the popsicle sticks holding together the sides popped off, so the main structure wasn't supported.
The Trusses
On the second bridge, the method to improve was to make sturdier and more secure trusses. To do this, we used our original truss design but added a second truss layer. This way the bridge would be more secure and the weight would have two layers of trusses to travel trough instead of one.
Most Important Aspect
The design of the bridge was built so that there would be multiple sticks supporting the main frame of the bridge. The bridge had three sticks running parallel with each other. This let the forces of the bridge go through various platforms instead of one, and it also was designed so horizontal sticks could be between the layers to increase the durability of the sides.
How Did the Forces Interact with our Bridge?
On the second bridge the improved connection on the top and bottom plus the stronger trusses made it so the bridge didn't bend at all. With this said the forces barely affected the bridge except for the section where the platform was held. This area saw heavy tension and was the only part of the bridge that snapped.
What was the weakest aspect of our Bridge?
This time the bridge was better built so the issue of weak areas wasn't an issue like last time. This time the main issue was that our group ran out of sticks, which we needed to se to secure the area holding the weight platform. Evidently this area was the only area to break at 151 pounds.
How did our Bridge Break?
Our second bridge broke because the support platform that held the anchor for the weights was not strong enough and it snapped. If we had moved the two sides of the bridge closer together so that the sides could be the supports for the block that held the weights our bridge could have held much more. After testing all parts of the bridge other than the support platform remained in tact showing that our bridge would still have been able to hold more.
Conclusion
After watching both of our bridges, and watching other group's bridges as well, we learned that a good bridge has a good main support, and a truss system. Our second bridge succeeded due to its support and connection, which was where our first bridge failed. In addition to this, our second bridge had a more secure truss system, and succeeded more than our first bridge. Trusses more evenly distribute the weight across all parts of the bridge, and helped the weight not press more against one individual part. In addition to this, we learned that a good bridge has a strong, secure place to hold the weight. Our second bridge broke because the part that was in place to hold the weight was not strong enough, and snapped.