How Do Stone Arches Stay Up

When you get to the top, you place the most important stone, which is called the keystone. It’s the center stone of the arch that holds the structure together. The keystone, when placed correctly, locks the other stones in position. Then, you remove the wood support and the arch remains standing.

How does an arch support itself?

Arches are compressive structures, that is, there are no tensile stresses. They are self-supporting, stabilised by the force of gravity acting on their weight to hold them in compression. This makes them very stable and efficient, capable of larger spans, and supporting greater loads than horizontal beams.

How does an arch not fall?

As the rise, i. e. height, of the arch decreases the outward thrust increases. In order to preserve arch action and prevent collapse of the arch, the thrust must be restrained, either by internal ties or external bracing, such as abutments.