Beam Bridges

A bridge can be defined as a structure which is built to span any physical object like rivers, roads etc. and provide a passage. Common types of bridges are Beam bridges, Suspension Bridges, Cantilever Bridges, Truss Bridges, Arch Bridges and Cable stayed Bridges.

Design of a bridge depends on various factors like its intended function, type of location at which the bridge is constructed and financial resources.



Quick Facts about Beam Bridges: –

  • A beam bridge is the oldest and simplest bridge design.
  • Beam bridges are level structures with supports on each end and sometimes additional supports (called piers) in the middle.
  • Various kinds of material can be used to build a beam bridge, like wooden planks, stone slabs or steel.
  • The Lake Ponchartrain Causewayis the world’s longest bridge. It is also a beam bridge.
  • A beam bridge is also known as a girder bridge. These bridgesare the least expensive ones to build.
A footbridge using beams
A footbridge using beams

Have you ever crossed a small stream or creek on a plank of wood or a fallen tree? If you have, you’ve used a beam bridge! The beam bridge is the oldest and simplest design and is also the cheapest style of bridge to build.

They are usually placed over highways, waterways, or other gaps in the landscape to allow people, traffic, and even animals cross safely. In the pictures below, you can see some examples of different beam bridges.

Footbridge over a small stream
Footbridge over a small stream

So what do all of these bridges have in common? What do you notice about how their structures are similar? Beam bridges are supported by a strong pillar at each end. In the footbridge pictured above, the beams are not very noticeable, but they are the structures that connect the bridge to the ground on either end.

The next picture shows another type of beam bridge that has an arc in the bottom. Do you notice how the surface of the bridge is a flat surface? That is a common feature in a beam bridge structure.

The third picture above shows a common design for a railway beam bridge, while the final image shows the longest beam bridge in the world. The Lake Ponchartrain Causeway is located in New Orleans, Louisiana in the United States, and it is nearly 24 miles long (38 kilometers).

Beam bridge that crosses the River Weaver.
Beam bridge that crosses the River Weaver.

As it was said above, beam bridges are not only one of the cheapest bridge designs, it is also one of the simplest. The two pillars located at each end are the main support structures and are used in beam bridges to disperse the weight of traffic and the weight of the beam itself.

If the bridge is fairly long, more supports may be needed in the middle. These are called “piers.” Most modern beam bridges are not made up of wood or logs, but with reinforced concrete and steel so they are strong and rigid.

Railway bridge in Finland.
Railway bridge in Finland.

There are three main types of beams that are used in the construction of beam bridges: – trusses (with the support beam over the top like the railway bridge above), box girders (like the beam bridge over the River Weaver pictured above), or I-beams (as seen in the Lake Ponchartrain Causeway).

Beam bridges are not always in the single span. Multiple piers can be used to support multiple spans. A beam bridge should never extend more than 250 feet without additional support structures in the middle section. If there is a need to build a longer bridge, then it will result in a series of bridges joined together.

Generally, beam bridges are not used for long distances because the increased distance between support structures can weaken overall bridge stability.