Real-World Stress Test

Our smashable structure For this assignment, our Building Materials and Construction class split into small groups and built structures large enough to hold an 8 x 8 x 14 inch box, out of any materials, joined any way except welding or soldering, with no member thicker than half an inch. They also had to have flat tops, because on the due date, we stress-tested them by loading them down with bricks — or people — until they collapsed under the load. They were scored according to how much weight they carried versus how much they weighed, with the most efficient structure winning.

Top view of structure
The "box of crosses" structure is clearer when seen from above

Adriana Garcia and I went through several designs until we settled on our competitor, which as seen above was a set of crosses lashed into a box shape. The interesting thing about this design is the way that it adapts to the load put on it. Though the dowels transfer some load to the ground as compression, the remaining force becomes a moment of rotation, spreading the arms of the cross. When the arms spread enough to tighten the lashing, the tension of the cable counteracts the rotation, and the structure stops changing shape. It was built of 1/2″ hardwood dowel, 1/16″ steel cable, screws, washers, and epoxy. Lots of epoxy. Steel cable is extremely slippery and treacherous, and unlike the fishing line we’d built the concept model with, would not stay wrapped tightly to the wood if left to its own devices.

Loading the structure with bricks
Adriana loading it with bricks

We also had to analyze how our structure would fail. I had expected the cable or glue to snap, but was wrong. Adriana accurately predicted that uneven loading or sheer strain would snap the wood around the screws where it was weak, and that then the structure would rotate and collapse. Our structure was middle of the pack for both the weight it took — about 480 lb — and for its effiency rating. The winning structures were all boxes built out of lots of simple X frame trusses. We had considered such a design, but decided against it. As well as being less original, it would have been expensive and difficult to build: we did not have a table saw, so instead of slicing a sheet of plywood into strips, we would have had to use expensive but weak softwood square dowel; neither did we have an accurate means of making angled cuts, so our trusses might not have fitted together accurately and thus not transferred force well.1

Structure finally smashes
It smashes to flinders!

Maybe some time I’ll build another iteration, one that lacks the flaws of the old — I’m sure it’ll have exciting new flaws of its own — out of dowel or pipe and rope. Definitely not from steel cable. You see, the concept model showed a lot of promise. It weighed at most half an ounce and held up almost 50 lb of bricks, a ratio of over 1000 versus one of 400-ish for the competition model. I’d like to see what it can do if I do a better job of building it.

  1. On that note, I don’t understand why Algonquin doesn’t give the Interior Design program any shop space, or access to the shops the college already has. Neither do they give us any space where we can make a mess cutting, glueing, etc. without getting complaints. This really isn’t fair in a program where most projects involve cutting and gluing, and many are much easier and better done with basic wood- and metal-working tools. Why doesn’t any of our tuition go towards providing us with them?