Earthquake Tower

Identify Problem

Design and build a small scale tower to be tested on an earthquake simulator for its strength or flexibility.

Constraints:

Made out of at most 14 1/8" balsa wood strips
Must be at least 18" tall
Must start at with at least 4" in width
Must have 5 floors, evenly spaced at 3.5" apart
Uses 5 weights (7 stacked washers each)
Joints must use wood glue or hot glue

Brainstorm

Research

In my research, I found that there are two different types of towers: rigid and flexible. Rigid towers are stronger and are built to not sway at all, just withstanding force through sheer strength. Flexible towers, on the other hand, are build with the intent to sway. This is usually done so that they absorb the shocks of earthquakes, which both reduces stress on the tower, and allows it to be built with less brittle materials, as the stronger materials tend to be more brittle.

I also found that a lot of towers will get thinner towards the top (like a pyramid), as this lowers the center of mass which, in turn, makes it more difficult to topple over. King Kong could easily knock over a skyscraper by applying force to the top of the tower, but he'd find it really difficult to knock over a pyramid for the same reason.

Sketch

The tower was intended to be quite flexible at the base, using 3D printed parts out of a rubber-like material (TPU), which would, in theory, absorb the shock of the tester at the bottom, allowing the top to just stay in place.

Design

The final design of the tower doesn't actually taper like a pyramid, as I initially intended. This is because when I tried to design the multiview of the tapered version, I realized that the vast majority of the weight wouldn't be in the trusswork, but the washers. Tapering is only effective because it uses less materials, and in turn, weight, at the top, but with the washers needing to be evenly spaced, it wasn't effective enough to justify the added difficulty of designing an angled multiview. I also designed a custom base for the tower so we could use TPU pilings (where you have vertical beams stuck deep into the ground) for added support.

Build

The major problem of the build was the TPU (flexible 3D printer filament). TPU is notoriously difficult to print with and degrades ridiculously fast. The filament I had was perfectly functional the last time I printed with it, but in the year it was left unused, it degraded so much to the point it was useless.

This made us have to rethink the base and we had the idea of using hot glue sticks for flexibility at higher frequencies, reinforced with balsa wood strips that were precut to intentionally break. This was done so that there was still some stability while the tower shook slower (as it would just fall over if it were just hot glue) but as it got faster, it wouldn't need as much support, so the wood would break off, leaving only the hot glue.

Test & Evaluate

Testing the tower consisted of putting the tower on a platform that shook it vigorously until it broke. The first parts to break were the artificial break points on the base but they didn't all break at the same time (shocking, I know) so it didn't have the same effect. Instead of allowing the bottom to wiggle freely and absorb all of the stress from the simulator, the tower just toppled over into a sad pile of broken wood.

Redesign

If I were to redo this project, I would use *new* TPU, ideally printed on a Bambu printer, for the highest quality and strength. I would also likely use a pentagonal design for the increased perimeter, adding more strength to the walls, as well as making it look nicer. Additionally, I would make the columns (vertical beams) inset, meaning instead of just being held on by glue, the floor would surround it, making the joint much less prone to breaking.

Conclusion

This project gave me insight on the major issues with designing towers, as well as the different parts of a skyscraper and the different designs. The biggest flaw with the project was that I didn't test the filament before needing to print, so I didn't have time to think of a better solution or even order new filament. In the future, I will make sure I have all of the materials before committing to an idea.

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