ARCH 245X–Spaghetti Bridge and Anthro Lab

November 12, 2010 § Leave a comment

Long time readers and SCI-TECH alums will recognize the pasta engineering to the left as the Spaghetti Bridge project, an introductory exercise we’ve used to start off our structures coursework in Iowa State’s M. Arch. program.  The last couple of weeks, Rob Whitehead and I have started a massively scaled-up version of the SCI-TECH structures sequence for our undergraduate program.

Our B. Arch. program is much larger–the class also includes second year interior design students–so we’ve had to scale things up from 16-20 students to, um, 120.  But we’ve decided to keep as much of the hands-on work as possible, and so far it seems to be proving itself even at the larger scale.

Spaghetti Bridge requires teams of 3-4 students to construct a structure that can span up and over a standard shoebox, and that can support a 200g weight at its midpoint for ten seconds.  We usually try to have students do as many iterations as possible–three has been ideal, but with time for weighing, testing, etc., we can only get two in during a 110-minute class.  Still, one of the points that gets made is that the iterative design process pays off–the second round involves bridges that are invariably lighter and more efficient than the first.

The winner–in fact the new all-time Spaghetti Bridge champion–is shown to the left.  Pedagogically this wasn’t the greatest outcome, since one of the things we try to stress is the usefulness of trusses in reducing weight of spanning elements (we put it in simpler terms than that).  The winning bridge relied on a bundled beam to span the box, but it used very lightweight tetrahedral supports that allowed it to carry the 200g weight with only about 18g of pasta, a “lunchable” amount, in the words of one SCI-TECH alum.  Students have to prepare a 4-5 page lab notebook after the class that describes their process and results, and these demonstrated that they did, in fact, pick up some basic principles of triangulation, depth, and stability.

The second lab in the sequence was one of Rob’s inventions, and it proved to be pretty brilliant.  Students were assigned to use their own bodies to demonstrate some basic structural types–columns, cantilevers, and simple beams.  How high, the assignment asked, can three people lift a 5-pound book?  Or how far can they extend themselves from a desktop?  Teams had to do these in advance of the lab, and prepare some summary images and text describing their efforts.  The entire class then voted on their favorites, and spent the rest of the lab time building concept models that embodied the principles at work in their anthropomorphic experiments.

The aspect of the lab that seemed to really work well was that students could feel the internal forces at work in their ‘structures.’  The student to the left, for instance, informed the class that his back and glutes were working quite hard to hold up his legs, but that he also felt it in his arms and shoulders.  Not surprising, we pointed out, given that a cantilever beam experiences tension on its top surface.  Likewise, the human Eiffel Tower below showed these students that stability works in multiple directions; the student on top said that she felt very confident that she wasn’t going to fall left to right, but she was quite nervous about falling to the front or to the back.

We’re waiting to get the lab notebooks back for this one, but already we’ve been able to use these images in lecture to talk about some basic equilibrium principles and structural types.  Beats doing free body diagrams and trig as an introduction to statics, we think, especially for designers who will likely never size a beam, but who will need to know the fundamental principles behind shapes, systems, and types.

More soon.  I should mention that this curriculum was developed in collaboration with Kevin Dong of Cal Poly SLO, and that several of the upcoming labs are directly borrowed from his outstanding work teaching structures to engineers and architects there.

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