Arch Bridges
An arch bridge is a semicircular structure. The design of the arch, the semicircle, naturally diverts the weight from the bridge deck to the ground.
Arch bridges are always under compression. The force of compression is pushed outward along the curve of the arch.
The shape of the arch naturally spreads the weight to the sides. There is little tension in an arch. The natural curve of the arch and its ability to spread the force reduces the effects of tension on the underside of the arch.
As with the beam bridge, when they get too big the weight overtakes the natural strength of the arch.
There are Roman, Baroque and Renaissance arches, all of which are architecturally different, yet structurally the same. Arches are fascinating in that they are a truly natural form of bridge.