1. Arch bridges
Arch bridges cannot bend, that is why they are made from many different types of materials such as masonry materials eg. Stone, brick etc.
Arch bridges have been around for many years and were first developed in the roman era.

2. Keystone in arch bridges.
The picture on the right shows what an arch bridge consists of. The stones join up in a semi circle and meet in the centre where the keystone sits. This keystone gives the main structure and support for the bridge.
The parapet is the second part of the bridges structure which gives extra support for the vehicles crossing.

3. Beam bridges
Beam bridges are very similar to arch bridges but consist of one long span of material Eg. reinforced concrete beam. When arch bridges were being developed, materials of this kind were not available.
Most of the beam bridges have pillars to support the weight and can be seen on motorway cross over to basic small stream bridges.

4. Cantilever bridges
The cantilever bridge is also similar to the beam bridge but is usually made from strengthened steel to support heavy vehicles such as trains.
They are able to reach longer distances and are in the shape of triangles which gives the extra support to the complex structure.

5. Suspension bridges The suspension bridge is mainly used for crossing
long distances in one
span.
The towers support the
main cables that are
attached to hanger cables
which are fixed to the
beam of the bridge. This
gives the ultimate support.

6. How it works.
The towers are attached into earth and the main cable is tied from the top of the towers to the end of the bridge.
The hanger cables are fixed to the main part of the bridge to give the extra support.