Architecture with polymers

My goal with this project was to find the most efficient way to use thin polymer tubes to build a bridge. I wanted to find what number and structure of straws held the heaviest load in relation to its own weight.

Link to infographic: https://infograph.venngage.com/view/add7959e-db8a-4f51-b5ec-3ab612324511

Materials:

Plastic Straws

Duct tape

Weights

Kitchen Scale

Hypothesis:

Bridges where the straws are inside of one another will have greater strength and efficiency because of the tension created when the straws located inside will try to unfold and push outward of the straws holding them.

PROCEDURE

Fold straws the lengthwise so that they remain the same length and you can insert them into non-folded straws.
Insert your folded straws into regular straws.
Repeat until you have two straws with one straw inside each, two straws with two straws inside each, and two straws with three straws inside each. Make sure to still have some hollow straws for later.
Tape two individual hollow straws together one inch apart at each end to prevent the limiting factor from being the straws sliding off of our surfaces.
Place the straws on two separate elevated surfaces so that one inch on each end is on the surface and the rest is elevated in the air.
Place weight on the center of the straws, progressively increase the weight until the straws fold from the weight and note how heavy the weight was when the bridge collapsed.
Repeat this for the pairs of double, triple, and quadruple straws.
Call this part 1. Save your data.
Tape 2 hollow straws together at the ends, and repeat this once.
Tape the ends of both pairs together so that they are one inch apart.
Repeat the last 2 steps with 3 straws together and 4 straws together.
Place the straws on two separate elevated surfaces so that one inch on each end is on the surface and the rest is elevated in the air.
Place weight on the center of the straws, progressively increase the weight until the straws fold from the weight and note how heavy the weight was when the bridge collapsed.
Repeat this for every set of straws.
Call this part 2 and save your data.

Results:

X Axis - Total weight of straws on bridge

Green Y Axis - Maximum weight in grams held by bridge

Purple Y Axis - How many times the bridge can hold its own weight (efficiency)

Part One (Straws inside straws)

Part 1:

These bridges became stronger with each straw added into the first straw. Each pair of straws added to the bridges resulted in the bridges being able to hold up to 500 grams more. The more straws led to more weight, maxing out at 1440g for 4 straws.

However, the ratio of mass of the bridge to mass of it's maximum load decreased, meaning efficiency decreased by our criteria. From single straw to quadruple straw, the max load of the bridge drops from 500x its bodyweight to 450x. Three straws showed the worst efficiency, being able to hold only 375 times it's own weight. The line of the best fit (purple line) shows a shallow decrease in weight to max load ratio as you increase straws with this method. One straw proved to be the most efficient.

Part Two (Straws next to each other)

Part 2:

These bridges are different from those from part 1 because here we are putting straws together, not inside of each other. This resulted in different results in terms of strength and efficiency. These bridges seemed increase their max load by 700 grams by adding one pair of straws. More straws led to superior strength gain, maxing out at 1720g for 4 straws

Unlike part 1, the ratio of mass of the bridge to mass of it's maximum load increased as we added straws. More straws led to a more efficient bridge. From single to quadruple straws, the ratio of mass to mass of max load increased by 50. The line of best fit (purple line) shows a slow yet certain increase in efficiency. 4 straws in part 2 led to the highest efficiency out of all tests in this experiment, being able to hold 550x its body weight.

This test did have an odd outlier. The two straws here was weaker in terms of max load than the single straws. No other test was weaker than the straws. I think this may have been more of a balance issue and strictly a strength issue. I taped the straws together so that they would be on top of one another, so when it experienced weight they slid off and folded more easily.

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