What does cardboard have in common with bicycles, kites, the Eiffel tower, and the Golden Gate Bridge? Triangles.
by Pearl Tesler • June 28, 2017
Dig a cardboard box out of the recycling, raise it up high, and bow deeply. You hold in your hands a miracle of engineering, one that rests firmly on the wide, strong foundation of geometry as applied to the weighty business of load-bearing: the triangle.
Triangle you say? Where in cubic void of this blessed Amazon Prime box is there a triangle?
Turn down one flap and look at the exposed cross section: Those wiggles we call corrugation are the structural descendent of a well-known architectural archetype, the truss.
No, no, not the undergarment. We’re talking bridges, rafters, roofs, and towers. In these structures, strength and stiffness are all, while weight is woe—and the secret to all three is triangles.
Here’s a simple experiment: Thread some string through four plastic drinking straws, and knot them together snugly. The resulting square can and does flex easily into a parallelogram, and even squash all the way flat. Now try again, but now thread only three straws together. The resulting triangle is rock solid—no flexing, no shape change.
Triangles also confer strength by distributing loads to minimize strain. As a heavy truck rolls across a truss bridge, the triangles of the truss redirects the downward force of the truck’s weight into tension and compression across the upper and lower layers of the span. Not only does this boost the bridge’s strength big-time, it simultaneously saves weight and materials cost.
Just like a truss bridge, the zigzags of cardboard that connect the two sides function to redistribute forces. Stiff and strong for its weight, corrugated cardboard isn’t the darling of the packaging industry for nothing.
So have a little respect for that box as you shove it into the recycling bin. And keep your eyes open for other triangles. In tools and toys, buildings and bridges, you’ll find them—wherever strength, weight, and stiffness matter.