OVERVIEW

The Romans were the first to use arches as major structural elements, employing them, mainly in semicircular form, in bridge and aqueduct construction and for roof supports, particularly the barrel vault. Their choice of the semicircular shape was due to the ease with which such an arch could be set out. Generally these arches, as we shall see, carried mainly compressive loads and were therefore constructed from stone blocks, or voussoirs, where the joints were either dry or used weak mortar.

During the Middle Ages, Gothic arches, distinguished by their pointed apex, were used to a large extent in the construction of the great European cathedrals. The horizontal thrust developed at the supports, or springings, and caused by the tendency of an arch to flatten under load was frequently resisted by flying buttresses. This type of arch was also used extensively in the 19th century.

In the 18th century masonry arches were used to support bridges over the large number of canals that were built in that period. Many of these bridges survive to the present day and carry loads unimagined by their designers.

Today arches are usually made of steel or of reinforced or prestressed concrete and can support both tensile as well as compressive loads. They are used to support bridge decks and roofs and vary in span from a few metres in a roof support system to several hundred metres in bridges. A fine example of a steel arch bridge is the Sydney...