The Titebond Bridge Rosa Bruno, Carmen Vigil, Kelsey Raley, Eric Elmer Executive Summary This project challenged us with the task of creating a bridge out of popsicles sticks and glue. The bridge had to be able to hold a minimum weight of 20 lbs and a maximum weight of 60 lbs. A bridge unable to support a 20 lbs minimum would put the lives of human beings in danger. On the other hand, a bridge that would support more than 60 lbs maximum would cost the taxpayers extreme amounts of money. These are two issues that our group has solved with the design process in bridge building. In order to build a successful bridge that anyone would feel safe traveling across with his or her newborn baby, we engaged in the design process with a game called Bridge Constructor. This gave our group of engineers the necessary background knowledge of functional bridge structures and ideal components of these structures, such as the use of triangles. We focused on not only making the bridge design safe, but economically affordable. We toyed around with multiple designs with background knowledge from Bridge Constructor. Our first design was over-engineered, following the motto: “When in doubt, make it stout.” This bridge structure held well over 60 lbs. Ultimately; following through with this design plan would protect bridge travelers, but would cost the already overburdened taxpayers more money than necessary. Putting in our own blood, sweat, and tears, we kept the consumer in mind as we went back to the drawing board. With the use of technology (photos and videos) we examined the superior structure points of our original bridge design. After pinpointing these points, popsicle sticks and glue were removed to reduce the risk for overspending on the budget for bridge materials.
Transcript
The Titebond BridgeRosa Bruno, Carmen Vigil, Kelsey Raley, Eric Elmer
Executive Summary
This project challenged us with the task of creating a bridge out of popsicles sticks and glue. The bridge had to be able to hold a minimum weight of 20 lbs and a maximum weight of 60 lbs. A bridge unable to support a 20 lbs minimum would put the lives of human beings in danger. On the other hand, a bridge that would support more than 60 lbs maximum would cost the taxpayers extreme amounts of money. These are two issues that our group has solved with the design process in bridge building.
In order to build a successful bridge that anyone would feel safe traveling across with his or her newborn baby, we engaged in the design process with a game called Bridge Constructor. This gave our group of engineers the necessary background knowledge of functional bridge structures and ideal components of these structures, such as the use of triangles. We focused on not only making the bridge design safe, but economically affordable.
We toyed around with multiple designs with background knowledge from Bridge Constructor. Our first design was over-engineered, following the motto: “When in doubt, make it stout.” This bridge structure held well over 60 lbs. Ultimately; following through with this design plan would protect bridge travelers, but would cost the already overburdened taxpayers more money than necessary. Putting in our own blood, sweat, and tears, we kept the consumer in mind as we went back to the drawing board. With the use of technology (photos and videos) we examined the superior structure points of our original bridge design. After pinpointing these points, popsicle sticks and glue were removed to reduce the risk for overspending on the budget for bridge materials.
As you will read about in the final report, the “Titebond Bridge” is the ultimate in strength to weight ratio design. This means the Titebond Bridge is on the cutting edge of innovative design as well as taking into consideration the cost to the consumer. There is no doubt that the Titebond Bridge is the bridge for you, your family, and your country.
The problem/task
Our task at hand was to create a bridge that could hold 20-60 pounds of weight. The requirements of our bridge were that it must be at least 12 inches long and 4 inches wide. However, the only materials allowed during our design process were popsicle sticks and wood glue. An added challenge for us to think about was the strength to weight ratio. Meaning how much weight our bridge could hold in relation to how much it weighs. Our goal was to create a bridge that held up to 60 pounds without the overuse of materials. However, if the bridge was able to hold over 60 pounds of weight that would indicate an overdesign in our bridge
construction. The real-life connection for this problem would be the consumer of the bridge (i.e.- taxpayers, government) would be paying for more bridge than what is actually required.
Final Design
Our final design consists of three equilateral triangles on each side, consisting of a triple stacked popsicle beam attaching the center points, which in the end create five triangles. The bottom consists of six X figures held together by a double layer of flat popsicles. The top has the same design, but only has four X’s due to there being less surface area. Triple popsicle beams extend the length of the bridge.
Engineering sketch of final design:
Photos of final design:
1. Bottom View2. Inside view3. Top view4. Side view
1. 2.
3. 4.
After testing this structure, we found that we successfully met the objective of holding at least 20 lbs of weight. Our bridge solidly held 30 lbs, but a joint unattached from the structure at 40 lbs. Although the cohesiveness of the structure was compromised due to the separation, the structure did not collapse and held the weight. This joint was connected only by wood glue.
None of the popsicles split, leaving the glue to be the weakest link in our structure. Had we been able to use another material to join the structures, the bridge would have held.
Narrative of Change
Our initial design consisted of pasting together popsicle sticks to create triangles. Based on our experience with the Bridge Constructor game we determined that triangles were the most reliable shape because of the balance between tension and compression. After constructing one side of three triangles and apply pressure to them, we decided that the lack of symmetry showed weakness. This led us back to the drawing board, where redesigned our triangle sides focusing on symmetry.
Our redesign consisted of equilateral triangular segments that were joined by small popsicle segments. We were diligent about how we glued our popsicle sticks together making sure that there was consistency in the pattern of layering and gluing of the sticks. This led us to our next task of creating the foundation of our bridge.
The X design came from our background knowledge of using the Bridge Constructor game. We noticed that when we set foundations for our bridges in the game, they were always in an X shape. In order to glue the x’s together we set a flat layer of popsicles between, similar to the wooden pallets seen in shipping warehouses or Home Depot. We duplicated our X design based off of these two pieces of background knowledge. When connecting the bottom pieces together, there was not enough surface area to connect the sides, so we added triple layered popsicles sticks to work as beams, providing surface area and extra support. We would then add a second layer of our X designed wooden pallets for more support. When connecting the 3 parts of our foundation, we found that the second X design layer did not fit. In response to this new challenge we decided to use extra triple layer popsicle beams to create triangle shapes.
The design for the top of the structure was also based on the Bridge Constructor game. It holds the same X wood pallet designs as the bottom of the structure. We thought it was important for our structure to have a top because the Bridge Constructor game showed us that the tension forces exhibited on the side and top bridge pieces reduced the amount of compression force on the bottom bridge pieces. In the Bridge Constructor game when we did not add any pieces to the side and/or top, the compression force exerted onto the bottom of the bridge was too much to support any vehicles. After adding the triangular pieces to the bridge sides and X design pieces to the top, forces exerted by the given load were distributed out almost evenly amongst the bridge pieces. Our group took this concept from the game and applied it to the “Titebond Bridge” we had been constructing with popsicle sticks. To improve upon the X design used in the game, we borrowed our idea for the bottom of the bridge structure by also using our X wood pallet designs for the top of the bridge. Our reasoning for using this design rather than just a simple X served as a solution to two of our challenges. Obviously, reinforce the bridge to support more weight. But also, the surface area created by the X wood pallet design allowed for a greater amount of space to create a joint between bridge pieces. This helped ensure that the
bridge strength would not be compromised by the integrity of the joints.
We tested our structure using increments of 10 lbs. There was no change in the structure until we placed 50 lbs of weight on it. We then heard small cracking sounds, but no popsicles or joints were broken. In the end, the initial structure held 65 lbs leaving us to conclude that it was over engineered.
We discussed which part of the bridge we felt were excessive in materials. We all agreed that the foundation was over designed. We took off the triple popsicles, leaving one layer of X wood pallet designs. We thought that the single layer of X pallets would do a good job of holding the weight and compression forces, yet weighed less as a structure than our initial design.
This design held its shape until 30 lbs when we noticed it began to sink in the middle of the bridge. Regardless of the shape change, all of the popsicles and joints were still in tact. We continued to add weight. The structure held through 30 lbs, but one joint detached at 40 lbs. At 40 lbs we had a joint compromised, which led to an overall bridge failure. None of the popsicles snapped, but the glue that held the joints did not hold.
Looking back on our design process, we did a lot of trial and error. Once we found that our design exceeded our expectation of holding 60 lbs, we thought of ways to optimize our design. By looking at what aspects of our structure were needed and not needed to support the weight of the bridge we modified by eliminating unnecessary components.
Lessons Learned and Wisdom for repeating
Many lessons were learned through the experience of building multiple components for our bridge. We determined that consistency was very important in order to build a reliable structure. Uneven surfaces, shapes, or glued joints could cause a weak area within our bridge. We had the opportunity to rebuild our initial tested design, taking into consideration the importance of consistency. If we could redesign again we would “test fit” the bridge segments as we went along in order to avoid gaps that required glue to fill them in. The filling of glue and lack of popsicles in certain areas may have made joints weaker. Our tested design had some uneven segments due to crooked popsicles that may have affect the even distribution of the weight. This may have stressed some joints more than others causing the break in the left joint that caused our design to fail.
In the broader aspect, if we were to create a real bridge we know that we would have created a blueprint and would not only be able to rely on trial and error. Looking back, it may have been beneficial to create a blueprint of our design manually or use a design software program to simulate the forces acting upon the bridge. It would have also helped us with accuracy by identifying consistent measurements needed to create a symmetrical and leveled bridge. The use of the software would have allowed us the same trial and error experience without wasting materials.As a team, everyone felt comfortable sharing their own ideas and also potential issues with the ideas of others. We worked democratically to make major decisions and compromised whenever possible. The final structure was an equally collaborative effort, in the sense that everyone’s ideas were used in some aspect. Openly communicating with a common goal in mind allowed us to work professionally and efficiently without the worry of hurt feelings. Our ability to compromise so well may have been a contributing factor in over-engineering. If we had challenged ideas more fully through testing, we might not have added so many unnecessary pieces.
