Physical Bridge

Rough Drawing

Fig. 1: Our plan for the physical bridge.

This drawing was not only the basis for our ModelSmart design, but the basis for our entire physical bridge. As you can see in Figure 1, we have dashes signifying each specific measurement we used for each section of our bridge. However, as we started building, we noticed flaws in our design that we had to come up with solutions for on the fly. For example, it would've been extremely complicated and unstable if we would've made our trusses go only halfway to the center and connect in the middle. If we had any error, that would result in breakage of the trusses and waste of precious materials. So, we decided to make our truss lengths 10.4 inches so we could have them span across the entire square of the truss. Additionally, we added a bar through the middle of the superstructure to enhance the stability of it. Since those sticks were so long, we figured that an extra connection would help with this.

We also planned our base on this drawing, as shown in the top right corner of Figure 1. However, we decided to add more to this base to make it more stable such as extra beams in the horizontal direction and sticks in the horizontal direction.

The process of drawing out our design taught us how plans can change very quickly- we must be adaptive to new ideas. Things that have been thought up in the planning process may not work in real life, and it's extremely important to be able to work around that.

Finally, before we could actually build our bridge, we had to keep in mind the constraints of materials and dimensions. Once we ran out of glue, we couldn't get anymore, which became a challenge especially when we wanted to add things to our design that weren't in the original plan. Additionally, we had to have our bridge be at least four feet long (and be three feet over a gap), have a one foot clearance (which is shown with the two X trusses that are each six inches tall in figure 1), and be at least five inches wide (with our superstructure, however, it had to be nine inches to fit the entire cart). This was reflected in our design.

Design Process

Fig. 2: Side view of our base structure before we added the extra support to it. As you can see, sticks are lined through the planks to minimize the stress in one area of the board.

Fig. 3: Front view of our base structure. As you can see, since we only had planks of three feet long and our design had to be four feet long, we alternated which side of the base had the small plank to reduce the chance of the bridge breaking because of a weak connection between planks.

Fig. 4: Extra support for the base that went under the base in figures 2 and 3. This was extremely important for our bridge because the trusses helped with distributing the stress of the force to other parts of the bridge.

Fig. 5: The under supports we added to the base of the bridge. Because of these horizontal supports (long ways and across) and extra sticks to stabilize the base, our base didn't actually break when the bridge failed. This design worked for us extremely well.

The base supports and understructure shown in figures 2-5 were the strongest part of our bridge. Since we added so many layers to the base along with the extra understructure, our base was able to take and distribute a lot of stress during our test. In the future, we would continue to use this design for our base with a few small alterations. We could add trusses to the understructure as well for extra strength or make the structure in figure 4 X trusses instead of triangle trusses. But overall, this design was great for our bridge.

The legs shown in figures 6-9 were the weakest part of our bridge. We didn't make these supports strong enough even with the addition of the planks and the vertical sticks. However, because we were out of glue, we couldn't do anything to remedy this issue. In the future, we should try to conserve glue and focus more on the legs of our structure. If we had stronger legs, our bridge would've been able to hold so many more bricks.

It was very interesting how the leg that was put together in sections broke instead of the leg that was put together piece by piece and objectively seemed like it would be less sturdy. However, after further evaluation, we realized that the sectioned structure wasn't evenly placed. One side structure was on top and one was on the side, causing for the bridge to fall.

Fig. 6: One of our unfinished legs.

Fig. 8: Front view of both of our legs.

Fig. 7: Top view of both of our legs. While one leg was built piece by piece, the other was built section by section. Because of this, our legs were uneven. To improve, we should communicate better as a group and make sure that we're on the same page about how each piece of the bridge is being built. That way, no inconsistencies will occur.

Fig. 9: Side view of both of our legs. The planks on these legs came from wanting to add extra support specifically to the legs of our bridge. Since our ModelSmart simulation stated that our legs had some of the greatest pressure points, we wanted to make sure they were as strong as possible. The planks added to their stability and resistance to the force of the bricks.

Fig. 10: The superstructure of our bridge. As you can see, this differs from the design we originally made on paper. However, after running the simulation in ModelSmart and online, we realized that this structure needed more support. This idea was great in theory. Where we went wrong, however, was how we put this middle bar on. Since it wasn't connected to the wood that would make our trusses have right triangles, the bar didn't provide as much support as it could've. In the future, we'll be sure to glue that down to maximize the functionality of our trusses.

The superstructure shown in figure 10 could've been more functional than it was, especially since it made it difficult for us to move the cart along the bridge. In the future, we will make sure this structure is stable and secure with glue before testing. We could also add extra wood planks to make sure that the structure doesn't bend inwards when more bricks are added.

Final Bridge

Fig. 11: Side view of our final bridge.

Fig. 13: Corner view of our final bridge.

Fig. 12: Front view of our final bridge.

bridge video 2.mov

Video 1: Our final bridge with all of our signatures!

We were extremely proud of our final bridge, especially after all of the work we had put into it. We chose this design because we thought it would be the most well rounded of designs. We wanted everything to be equally strong, especially when it came to high stress from the bricks. So, we made sure that we focused on the base of the bridge as much as we did the legs, superstructure, and understructure of the bridge. Because of this, our bridge was able to hold more bricks than most others.

Bridge Test

bridge video 1.mov

Video 2: Our bridge breaking after holding ten bricks (about 45 pounds)! This was extremely exciting especially since we worked so hard on this project.

BRIDGE VID.mov

Video 3: The slow motion version of our bridge video. This allows for us to get a closer look at what went wrong.

Error Analysis

After seeing our bridge fail, we noticed what went wrong and how we could improve our design for the future. First of all, before the bridge even fell, we realized that our superstructure was bending in and therefore making our bridge very narrow. This was because that structure wasn't as strong as it could've been, and a lot of stress from the bricks was causing this structure to bend. Because of this, when we were pulling the cart through the bridge, it would get caught on the superstructure and trusses from it would break. It also made it very hard for us to fit bricks onto the cart, which caused us to take way too long trying to orient our bricks on the bridge. This caused extra stress on the bridge. Additionally, as shown in videos 2 and 3, our bridge failed at the left leg, which couldn't hold the force of the base and the cart. This was just what the simulations predicted, which showed that even with extra support, we should've made our legs stronger. If we would've spent more time on our legs, it likely could've held the weight necessary to carry more than ten bricks.

Candid Pictures!

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