There are many types of bridges including: Bridges are structures used to cross obstacles such as a body of water, a roadway or a low area of land. There are many types of bridges including: Beam, truss arch, suspension cable-stayed.

Bridges There are several types of bridges: Beam Truss Arch Suspension Cable-stayed

What type of bridge to build Determining the type of bridge to design, several factors must be considered such as: The length it will span The location and purpose Weather conditions - The load it will carry cost

Type of material They can be made of many materials, such as wood, steel, concrete, iron, stone, aluminum or a combination of more than one material. The type of material used depends on the type of bridge to be built and what the bridge will be used for. For example, wood can be a good material for a walk bridge but not for a very large highway bridge over a large body of water.

Vocabulary Bridges experience 3 major forces: Compression – a pushing force resulting in the load carried by the bridge and by the weight of the bridge itself. Tension – a pulling or stretching force that results from the compression. The greater the load, the greater the tension. Torsion – a special kind of tension force that results in the twisting of the roadway as a result of wind.

vocabulary Live load – the weight of anything that moves on the bridge and is not part of the actual bridge Dead load – the weight of the bridge itself Total load – the combination of the live and dead load.

Pushing on the top will stretch out the bottom

Torsion forces twisting the roadway

Beam Bridges A beam bridge is the most common type of bridge. It can be anything from a simple fallen tree across a stream to a very long bridge across a large body of water.

Characteristics of beam bridges The simplest type of bridge The ends of the bridge are supported by structures called abutments Usually used for short distances ( 250 ft or less) To extend the length, supports called piers must be used. The distance between 2 supports are called spans. Can be constructed of any material

Most railroad bridges are beam bridges.

More examples of beam bridges

Beam bridge

Truss Bridges Truss bridges are a form of beam bridge. However they have added support in the form of triangular shaped beams called trusses which are usually made of steel. The triangle shape provides more support because the force is split between the 2 sides of the triangle.

Examples of truss bridges

Compression/tension forces on beam and truss bridges Compression forces are on the top of the decking which is the roadway. This causes the bottom of the bridge to experience a stretching or tension force, with the center spot being the weakest.

Arch Bridges Arch bridges – one of the oldest types of bridges and were originally made of stone. The roadway can be found above or below the arch. The load of the bridge pushes down on the arch and the force pushes out against whatever is holding the arch in place.

This type of bridge has only compression forces acting on it.

Ancient stone arch bridge

Suspension bridges Suspension bridges are designed to have the decking suspended from cables. Two huge cables are strung over two towers and attached to the roadway by many smaller cables called suspenders . The ends of the huge cables are held in place at either end by concrete blocks called anchorages.

Compression and tension forces on suspension bridges

George Washington Bridge

Golden Gate Bridge

Brooklyn Bridge

Suspension bridges Used for long distances High above the water so ships can easily sail under them No piers to get in the way of ship traffic Cables are held tight by anchorages on land at either end. Decking must be reinforced by trusses to prevent torsion.

Trusses reinforcing the decking

Suspension bridges Made from steel and reinforced concrete ( concrete with steel inside) Tension forces on all cables Compression forces on towers and decking. Torsion forces on decking.

Cable-Stayed bridges A form of suspension bridge but does not use the two cables that identify the typical suspension bridge. Instead, individual cables are connected to each of two large towers, usually in a fan shape.

Characteristics of cable stayed bridges Ideal for shorter distances than suspension bridges where ship traffic occurs. Beautiful design Often have beam bridge sections on either end Cables hold up decking and are under tension Compression forces are on the decking and towers

Comparison between design of suspension and cable stayed bridges

Cable stayed bridges

Sunshine Skyway Bridge

Cable stayed bridges