Week 2 - Bridges
This week we dealt with Civil Engineering, which is the discipline of designing and building physical environment, which includes many public works like roads, bridges, various buildings, and dams. For this specific project, we focused on bridges.
These are small sample bridges made out of index cards to show how adding more supports are able to help keep bridges held strong together.
The more triangles and shapes, the more nuts these bridges were able to hold. We could fit over 50 nuts on the last one, but after that the bridge could not physically hold this.
Using Bridge Designer, we were able to design a truss bridge under specific requirements for compression and strength. There was a lot of tweaking required for specific sizes in order to have members that were strong enough to support very heavy loads.
We noticed that by making members really thick, the amount of force they could support increased drastically. We made sure to remember this in our design.
These were the specific forces that each member faced: by increasing the size of the top and bottom members, we were able to get pretty strong members.
The requirements were:
Under .40 Compression
Under .45 Tension
We had some close compression and tension, but a majority of these were far under the requirement.
The final price of this bridge was near $320,000.
THE DESIGN
Using ModelSmart 3D, we made a quick prototype that could undergo simulations for our real bridge. There were many limitations and difficulties with this software, but we were able to figure out many of these issues.
Similar to last week, we had many issues with connecting to the virtual machine that hosted this software. As a result, we could not get very far in this specific development.
3D Model
Using an online CAD software, we designed a truss bridge that we would use as a reference for our real bridge. This model was 3D printed in class.
We also tried to make a model with simulations in ModelSmart3D, but like last week, our connection kept getting booted and we were unable to finish it. We decided to focus on the actual building since we had time for that.
This is the 3d printed version of our model. After deliberation on our final design, this would not be the only thing present: we would also add supports on the bottom (see below).
THE BUILDING
Our first course of action in the real build was to make the base strong. We did this by making it around 3 layers thick, which would make it stiff and less prone to bending. However, we accidentally measured it a bit short, so we ended up needing to add on a bit.
We put measurement lines whenever necessary in order to measure out how much we needed to cover, cut, or glue.
We decided to add a small support structure on the bottom just for added stability. In order to do this, we would need more room above the 1' clearance requirement, so we designed our legs to be 1.5 feet long to give that extra space.
We made legs using 25 sticks that were 1.5' long each. This allowed for the full clearance of 1 foot while still having 6 inches for support on the bottom. These 4 sticks would act as the 4 legs, which would be connected on the bottom for more stability throughout the structure.
*The tape was later removed after this image*
Half built, this was our bridge with everything below the base made.
We proceeded to add on the supports on the top.
This was our first prototype of the bridge with top trusses built.
With more time left (and more resources after trading), we decided to expand more on supports to help this bridge hold more.
Sal working on adding layers to the bottom of the base:
RESULTS
Our bridge collapsed on the fifth brick that was placed. We were one of the first groups that collapsed, so it was actually quite comical and fun to watch it go down.
As we saw other bridges being tested, we realized several things: we did try to make some materials as thick as possible, but there were many other groups that had thicker supports. If our supports were more grouped together and layered, our bridge would have been able to hold up better. At the same time, some of the specifications of our bridge did make it more prone to falling: it was much wider and taller than other bridges. These design choices definitely were not the best decisions, but they were what we had.
