Project 2, Team A1

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Synopsis of bridge scores

  • α squad score:
  • Ω squad score: = 2.082528 * 10 -6
  • Current best team score: 2.0567 * 10 -6

Team members

Yewande Alade (α squad)

Helleh Balch (α squad)

Katherine Bertaut (Ω squad)

Shiv Bhandari (Ω squad)

Report

Final Design

A1 bridge.jpg

The main goal of this bridge design project was to create the lightest structure possible that could support the most weight, using the displacement analysis of COSMOSXpress.

We looked at using triangles because they distribute weight fairly evenly and are very rigid. Both the α squad and Ω squad had independently developed bridges using triangles, so the only reconciling we had to do between the two designs was the size and orientation of the holes. As the α squad had some weak points in their design that did not exist in the Ω squad, we started with a design that was closer to the Ω squad’s design. We also incorporated an important idea of the α squad--cutting out material from the base of the bridge.

We tried many different orientations and sizes for the triangles, however not all of the changes that we made turned out to be improvements.

We used fillet function to round the corners of the triangles as we noticed that stress was collecting at the corners. Even though this increased our surface area slightly, we were pleased to notice that the better stress distribution it afforded decreased the deflection enough to give us an overall lower score.

The circles included in our final design were created because we had not used as many openings as we were allowed to have. We put them near the base because the stress analysis indicated that there was little stress in the area. We determined their size by trial and error, looking for a size that was small enough to not adversely affect the displacement score but large enough to reduce the surface area of the bridge.


Ω Design

A1 omega1.jpg
A1 omega2.jpg

The Ω group originally worked on a design that used many parallelograms, as is shown at left, to distribute the weight towards the sides of the bridge. We worked on this design for quite a while, trying to perfect the design, running COSMOSXpress each time to see if the changes improved or hurt the total score. We then decided to see how a bridge that looked more like a standard truss bridge would work, and discovered with experimentation that it had a much higher score. From there we worked on the design slightly more. At the very end we started to round some of the corners, however we ran out of time before finishing (and also had a final surface area slightly over the maximum allowable value due to the rounding).


α Design

Image:A1BR.zip

When initially given the task to build a bridge, our group immediately thought to incorporate triangles. It the world of engineering it is widely regarded as the most structurally sound of all the geometric shapes. We cut a variety of "equilateral" triangles into our template. Initially, we left the edges of these triangles pointed, but then we found that these regions attracted a lot of stress. We then rounded (filleted) these edges to spread stress more even throughout the structure. We also thought that the amount of material at the bases of the "bridge" were not very important to the strength of the structure. It was this impression (as incorrect as it was) that made us cut out circular shapes at the bases. We thought that this would make the structure lighter (decreasing surface area), while having a minimal effect on the "bridge's" sturdiness. It was after our project was completed that we came to the realization that the bases were actually the most important part of structure and were the the regions where all the stress applied to the bridge collected.

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