There are five different basic types of bridges:

Beam Bridge

The "Beam Bridge" is a good design when trying to span a short gap that is also not very high. It is supported on either end by land or tall columns. If a beam bridge must be longer, support columns can be used to maintain support throughout the span. Materials used are usually concrete and steel.

Confederation Bridge between P.E.I. and New Brunswick is a Beam Bridge although it incorporates an arch between beams.

Truss Bridge

The "Truss Bridge" is similar to a beam bridge except much stronger. These bridges use a pattern of geometrical shapes (triangles) called trusses. These trusses are very rigid (they don't move when pushed) and, thus, make the bridge very STONG! Because of their strength, truss bridges are often used for railway bridges as they must be able to support the great mass and the vibrations of the trains.

Arch Bridge

The "Arch Bridge" is quite economical (cheap) to build. It can span a very deep chasm and maintain support throughout the span. The arch bridge is strong because no one point along the arch supports more mass than any other point - thus, the mass is spread out VERY evenly --> force spread out both downwards & outwards from the centre. Modern day arch bridges (they were used as far back as the Roman Empire!) use both steel and reinforced concrete as the basic materials. Arch bridges made of steel are constructed by joining curved beams of steel. The building process is interesting. Builders start adding the curved beams at either end of the span until they meet in the middle!

See a close-up of the arches of Confederation Bridge in Canada (although Confederation Bridge is really a "Beam" Bridge).

One of the most famous and widest steel arch bridges is the Sydney Harbour Bridge in Australia.

Cantilever Bridge

The "Cantilever Bridge" is constructed from two beams jutting out from either side of a riverbank or body of water (embankments). These two beams must be securely anchored into the embankments using concrete slabs called abutments. The two beams meet in the middle of the bridge. If the bridge needs to be longer, then a third beam is added between the first two and this third beam must be supported by a pair of columns or a centre pier. Look at the picture above.

The longest cantilever bridge in the world is in Quebec and it crosses the St. Lawrence River. It is called the Quebec Bridge. The main span of this bridge is as long as SIX football fields laid end-to-end!!

Suspension Bridge

The "Suspension Bridge" is the best kind of bridge to build when trying to span a very large body of water. The deck or roadway is supported easily by steel cables that curve from one tower to another tower. What Gives? Take a look at happens when a car drives across a suspension bridge . . .
The Launtau Link is the world's largest suspension bridge . . .

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Background image is Edmonton's LRT Bridge under construction