Bridges

As its name suggests, the main supporting structure in an arch bridge is one or more curved elements. The dead and live forces that act on the arch bridge are transmitted along the curved line of the arch into abutments at either end. These abutments are sunk deep into the earth, into bedrock if at all possible. They are, therefore, essentially immovable and able to withstand very large forces exerted on the bridge itself. This structure is so stable that piers are generally unnecessary in an arch bridge.

The deck of an arch bridge can be placed anywhere with relationship to the arch: on top of it, beneath it, or somewhere within the arch. The deck is attached to the arch by vertical posts (ribs and columns) if the deck is above the arch, by ropes or cables (suspendors) if the deck is below the arch, and by some combination of the two if the deck is somewhere within the arch.

Most arch bridges today are made either of steel or of reinforced concrete. The longest existing steel arch bridge is the New River Gorge Bridge in Fayetteville, West Virginia, built in 1977. It is 1,700 ft (518 m) long. The longest reinforced concrete bridge is the Jesse H. Jones Memorial Bridge at the Houston Ship Channel, Texas, with a length of 1,500 ft (455 m).