A catenary arch is a remarkable thing -- just think of the grandeur of the Gateway Arch in St. Louis, the tallest man-made monument in the United States. And it all started with observations from scientists and engineers of centuries past who wondered why a chain or cable always makes the same curve when it hangs -- the word catenary itself means "chain" in Latin.
The scientist Robert Hooke made the connection in the late 17th century between the curve of a hanging chain and a strong arch that essentially was the same curve inverted. "As hangs the flexible line, so but inverted will stand the rigid arch," he wrote.
The weight, or thrust of force, of the pieces of a catenary arch are directed almost entirely downward, so the arch can support itself without the need of surrounding walls or buttresses.
Fascinated by this structure, I made a model using wooden building blocks cut from an ordinary pine lumber that can support its own weight and an additional load. I can even sit on the model if I remain very steady, but I don't recommend it as it is rather uncomfortable!
This photo shows the arch holding up a weight of about 9 pounds, approximately 8 times the combined weight of all the blocks. I demonstrated the model at the Maker Faire Detroit in 2011 at the Henry Ford Museum in Dearborn.
For photos and tips on how to build this model, go here.