Week 3:

Civil Engineering

Bridge Design Kit

We started this week by creating a truss bridge made out of paper. We went through several directions by adding parts to the bridge. After each change that we made, we tested how many metal nuts the bridge could hold before breaking. This kit helped us understand engineering concepts and building skills that go into the design of bridges.

Activity 1:

note: The first design doesn't include the sides

The first part of this activity was to allow us to understand load. With just a cue card in between the wooden blocks, this bridge design allowed only 4 nuts until it collapsed. The cue card experienced bending stress due to the concentrated load of the nuts, so load increased, the bending moment exceeded the card's capacity, causing it to collapse.

Activity 2

The second part of this activity was to allow us to understand stress. With the previously used cue card, we added a structure on each side of the bridge . By adding the supports on each side of the bridge, it helped distribute the applied load more evenly. This reduced the concentration of stress on the middle section of the cue card, allowing the cue card to hold 7 nuts.

Activity 3

The final section of this activity was to deepen our understanding of stress, where we taped two strips as the top cross bars of the bridge. This connection between the two trusses and allows for even more distribution of force to withstand the load of the nuts. Our bridge was able to hold 11 nuts before falling.

Tinkercad

The next step was to roughly model the bridge in 3 dimensions. We accomplished this by making a model in Tinkercad, a Computer-Aided Design(CAD) software. This allowed us to see how the final bridge might look like, and also roughly identify a blueprint to follow when constructing the Balsa wood bridge. Even though we eventually used a different design, this step was very helpful in the design process.

Tinkercad Design Side View

Tinkercad Design Front View

3D printed

These designs are similar to our final bridge design, as we modified some elements in the building process. Designing in Tinkercad was fairly intuitive, as the tools were easy to navigate. That being said, these models were not very realistic or to scale; which limited their translation to our physical design.

Designing the Bridge

After building the design in Tinkercad, we started drawing up the design plan for our wooden bridge. We took into mind the requirements of the structure, as well as the properties of the Balsa wood planks and sticks. Taking all of this into mind, we did the measurements and began preparing the materials. We would later realize how important this step was.

Bases

These are the bases of our bridge. On the inside of the basses is a blank that goes diagonally in the box that we made for our base. Since the bases is only 3 inches in width and length, it would cause our bridge to wobble since the board of the bridge was 9 inches.

Building the bridge

In this picture, the board of our bridge is supported by trusses on each side. We decided to use a Howe's truss because it was cheap and didn't require that much materials to build. However after building both sides, we realised that we should have doubled up the wood we used, so we had to individually glue more sticks on which was a very tedious process.

IMG_1176.mov

Final Product

The final product of our bridge was able to withstand a total of 3 bricks. The wobbling was definitely an issue, however so was the thickness of the trusses which caused the side to break. We should have used more materials since we had a lot leftover, but in the end, it was a very interesting experience.

6Research Paper

Group 6 Week 3 Research Paper

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