Great moments in engineering: The flying buttress

Find out about fantastical feats of fearless architecture, and how the buttress supports the arch.

For a while, the most impressive home people could boast was a nicely painted cave. After that, huts were de rigueur, since they required structures to be built. Since then, humankind has been getting fancy. One of its early fancy inventions is the arch. An arch is a precisely balanced series of blocks, pushed into a bow.

Or, more precisely, pushing each other into a bow.


Great moments in engineering: The flying buttress

The top of the arch stays in place because the sides put enough pressure inwards that the top stone can't shove them aside and consummate its life-long love of gravity. The sides keep from toppling inwards because the top keeps a steady push out on them. It's a constant stalemate. The stalemate in enforced by heavy pillars or walls at the base of the arch. These provided the base which allowed the sides of the arch to push inwards, keeping the top from falling in.

The work of these pillars is mitigated by several factors. A long smooth arch, like the curve of a chain when it hangs down between two poles, is easier to keep up than steep one. In a shallow arch, each of the blocks is pushing inward. In a sharp one, the bottom block push up, providing little support, the top one pushed directly down.

Great moments in engineering: The flying buttress

Slightly sloping outer walls on the pillars are also a stabilizing factor. Not only do they add bulk, which resists the outward push of the arch, but they exert an inward push of their own. The combination makes the arch more secure.

All of this stability was stripped away as the Gothic style of architecture swept in. Walls went higher, arches got sharper, and all of it got thinner. Especially the windows. Suddenly, instead of solid Romanesque bows supported by thick walls, people were building sharp curves kept up by glass.

Great moments in engineering: The flying buttress

Enter the flying buttress. One of the most dangerous-looking things in architecture – a giant stone pillar supporting a giant stone beam that pushes into a building, is the best way to keep those paper-thin walls up and the arches on top of them reaching for the sky. The flying buttress provides the push inwards that the wall itself is too insubstantial to do.

Via History for Kids, Ignoring Friction, Buttresses, and The Naked Scientist.