Arch Type

In this type of bridge, the weight is carried outward along two curving paths. The points where the arch reaches the ground keep the bridge up by resisting the outward thrust. The roadway is located on top of the arch.

Materials and Construction

Like beam bridges, arch bridges can be made of both steel and concrete.

Steel Arches

There are a few different methods used to construct steel arches. One design uses an arch structure with the trafficway passing through the arch. The trafficway rests on the part of the arch it passes through. Cables, suspended from the arch, pull the trafficway up so it does not sag.

That type of bridge is construced through this process:

  1. The anchors for the arch are constructed. The arch is started and is supported by temporary steel cables on either side securely anchored in rock. These cables will hold the arch until it is completed or very close to completion.
  2. Cranes are used to build the arch. They are placed on the exisiting fraction of the arch and lift the steel to its proper position, and then they erect it.
  3. When the arch is fully built, the temporary steel cables are disconnected and the cranes put the trafficway in place.
Another method used is one that is useful when the other type of steel arch bridge is not possible. It is built by building an arch (which is often supported by pillars until completed) and then building a traffic deck above the arch. The traffic deck is supported by pillars. It's almost like a beam-type bridge on top of a steel arch!

Concrete arches

Most concrete arch bridges are built in the same way. They consist of an arch which has pillars that support the road deck, which is held up by the arch. There also are concrete arch bridges on which the traffic 'rides' directly on top of the arch.
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