How Arches Work! (with Diagrams!): Structures 2-2

Arches are the opposite of cables. Arches work in compression while cables work in tension. Arches are rigid while cables are flexible.

And, for the same loads, the shape of the thrustline within an arch is the same, just inverted, from the shape of a cable.

So we can look at thrustlines within arches. They tell us a lot about the behavior of the compression force within the arch. If the thrustline stays within the arch then there are no concerns (here, we’re assuming the arch is made of rigid blocks that can’t carry tension between them). But, if the load is to the side we see how there can be a problem as the thrustline leaves the arch itself.

We then go through a range of other loads on an arch and how the internal thrustline changes. Each time, we compare the thrustline to the corresponding shape of a cable.

We finish with the concept of arch bridges and that of a tied arch putting tension into the deck so the end supports can be vertical-only.

Don’t forget to like and subscribe!