Bridge Kit

Since none of us had really ever worked with civil engineering and bridge building before, we wanted to start with a simple bridge to extend our knowledge. Using the BridgeKit, we were able to see what it looked like when a paper bridge had different amounts of support from joints and members. This helped us immensely when thinking about our design for the physical bridge because we realized that trusses make bridges so much stronger, especially as superstructures. This was one of the reasons we incliuded a superstructure in our physical bridge.

Step 1:

Create a paper bridge by placing a piece of paper between two blocks of wood four inches apart. Add bolts to the piece of paper until it bends into the space between the blocks.

Number of bolts: 3

This test proved exactly why support is necessary for bridges. Because there was nowhere for the force of the load to spread out and lessen in each joint and member, the force downward took the bridge with it, as shown in Figure 1.

Fig. 1: Our paper bridge using only a single piece of paper. As you can see, it could only hold a small number of bolts before it bent completely to the ground. This is because it didn't have any support to keep it from bending.

Fig. 2: Our paper bridge with one truss on each side of the paper bridge. As you can see, this bridge could hold a much larger load due to the support the trusses gave the bridge. This was extremely interesting, and it gave us much insight into how our bridge could be stronger using the support of trusses.

Step 2:

Number of bolts: 10

The only change we made to this bridge was the two trusses on either side of the paper. However, it proved to have a major effect on how many bolts the bridge could hold. The trusses allow for us to counter the normal force of gravity exerted over the bridge. Instead of the entire force of gravity of the load going straight down, the force was distributed in two separate areas in the form of trusses, as shown in Figure 2. This can also be explained in terms of stress. Instead of the stress of the bridge, which would steadily increase as the force from the greater mass/number of bolts increased and the area stayed the same (force/area=stress), being only limited to the singular piece of paper, the stress is distributed to other parts of the bridge, decreasing stress in one area of the bridge. This allowed for the bridge to hold a larger load than the bridge in Step 1.

Step 3:

Create a bridge by taping four one-half inch by three inch strips of paper to create two arches and connect them to the piece of paper. Place the piece of paper between two blocks of wood four inches apart. Next, tape one one-half inch by three inch corner strip to each edge of the bridge connecting the bottom of the trusses to the strips. Then, tape two strips of the same length to the top, connecting the corners and the trusses. Add bolts to the piece of paper until it bends into the space between the blocks.

Number of bolts: 19

This bridge held more bolts than the previous because of the addition of right angles to our trusses. The combination of right and equilateral triangles for our trusses made for an overall stronger bridge due to even more force allowed to be distributed as well as more points where the force can be distributed, as shown in Video 1. This lessens the stress because of this, allowing for a larger load to be put on the bridge without it collapsing. This was also something we pocked for our physical bridge- we wanted to create as many points as possible for the stress to go so our bridge wouldn't collapse and the force of gravity would be minimized. However, we felt like we could get even more bolts onto the bridge without it collapsing, which is what happened in Step 4.

a great bridge vid.mov

Video 1: Our paper bridge with one truss on each side along with extra supports coming from the corner and top members. This helped with the support of the bridge, but not as much as we would've hoped.

Fig. 3: Our paper bridge with one truss on each side along with strips of paper connecting the trusses in the corners and between trusses (across the bridge and along it).

Fig. 4: Our paper bridge from a different angle.

Step 4:

Create a bridge by taping four one-half inch by three inch strips of paper to create two arches and connect them to the piece of paper. Next, tape one one-half inch by three inch corner strip to each edge of the bridge connecting the bottom of the trusses to the strips. Then, tape two strips of the same length to the top, connecting the corners and the trusses. Finally, cut two one-half by two and a half inch strips and attach them from corner to corner in the opposite direction. Add bolts to the piece of paper until it bends into the space between the blocks.

Number of bolts: 34

The load in this structure is almost double of what the previous bridge structure could hold due to the horizontal support beams that were added between the two trusses on either side of the bridge. Due to these added beams, the stress in this structure was distributed evenly among the base and both trusses on either side of the base. This meant that the bridge could hold more weight than before, and the beams also prevented the side trusses from falling down to the side. The flow of forces flows from all the directions from the center and travels up the trusses. When it reaches the trusses it gets equally divided into the vertical and horizontal members which distributes the stress in a way that allows for the bridge to hold a much larger load. After doing this test, we realized just how important trusses would be for the structural integrity of our bridge. So, when we started designing, we kept the things we learned from these tests in mind.

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