The Arch Bridge

An arch bridge is a semicircular structure with abutments on each end. The design of the arch, the semicircle, naturally diverts the weight from the bridge deck to the abutments.

Compression
Arch bridges are always under compression. The force of compression is pushed outward along the curve of the arch toward the abutments.

Tension
The tension in an arch is negligible. The natural curve of the arch and its ability to dissipate the force outward greatly reduces the effects of tension on the underside of the arch. The greater the degree of curvature (the larger the semicircle of the arch), however, the greater the effects of tension on the underside.

As we just mentioned, the shape of the arch itself is all that is needed to effectively dissipate the weight from the center of the deck to the abutments. As with the beam bridge, the limits of size will eventually overtake the natural strength of the arch.

Types of Arch Bridges

Dissipation

Arch types are few -- after all, an arch is an arch. The only real subcategories come in the form of cosmetic design. There are, for example, Roman, Baroque and Renaissance arches, all of which are architecturally different but structurally the same.

Arches are fascinating in that they are a truly natural form of bridge. It is the shape of the structure that gives it its strength. An arch bridge doesn't need additional supports or cables. In fact, an arch made of stone doesn't even need mortar. Ancient Romans built arch bridges (and aqueducts) that are still standing, and structurally sound, today. These bridges and aqueducts are real testaments to the natural effectiveness of an arch as a bridge structure.