As you might imagine, bridge construction can be a complex operation; there are many possible building methods involved in the production of a bridge. As you drive across one of these impressive feats of engineering, you may find yourself wondering how exactly they are built.

Like any other large-scale construction project, a multitude of factors must be considered before the method of construction can be decided upon.

The following are some elements that must be considered before an appropriate construction method is settled upon:

• The obstacles the bridge will cross and encounter.
• The soil makeup.
• The scale of the bridge.
• How easily the site can be accessed.
• The local weather.
• The costs of local material and labour.
• The deadline of the project.

Types of Bridge

The three basic types of bridge include:

1. Beam
2. Arch
3. Suspension

Beam Bridges

These bridges are usually made from steel truss or concrete units; a self-supporting beam will transmit loads through its vertical supports. Here, simple beam or cantilever methods are used in construction.

Arch Bridges

The stability of these structures, usually made with concrete arches, enables them to carry greater loads than bridges supported by beams. The load-bearing arches are in a state of compression which provides the bridge with its strength.

Suspension Bridges

These bridges use vertical towers that are secured by cables suspended from a central deck. Cables are usually secured through anchorage tunnels.

A suspension bridge

Now that we know the basic types of bridge let’s take a more in-depth look at construction methods.

The Segmental Method

This is a popular method of construction as it helps create a structure of both an aesthetically pleasing and cost-effective nature. The versatility of this method means that it is used across the world and can be utilised for many different bridge types.

Segmental bridges are made in short sections; small pieces are built separately and then joined together in their final positions to form the full structure.

Segmental bridges are constructed with two different methods; precast and cast-in-place construction.

Precast Construction

The use of precast concrete refers to a method where the bridge sections are built at a secondary location and then transported to their final positions in the structure.

Cast-in-Place Construction

This refers to when a bridge is fully constructed in its final location. It is built in the ‘place’ where it is intended.

A concrete bridge

The Cantilever Method

As previously mentioned, beam bridges make use of this construction method. The cantilever method uses ‘cantilevers’; these are beams that are supported by only one end. Cantilevers provide lots of space below a beam because there is no need for extra supporting columns.

It is a method used for reaching over large spans; two cantilevers extend from opposite sides of a crossing to meet in the middle where a central truss bridge is often located.

This kind of bridge can also be used with either precast or cast-in-place methods.

A bridge with cantilevers

Caissons and Cofferdams

A caisson is part of the method used in bridge construction when part of the bridge is being built in an area submerged by water. They are box-like structures built around areas where underwater bridge piers or foundations need to be constructed.

Cofferdams are a similar concept but are temporary structures that are removed after the bridge work is completed. Caissons stay in place as part of the final structure.

Here, we have selected just a few bridges and construction methods to discuss, but we’ve barely scratched the surface!

If you require expertise in structural engineering or surveying, then Martin Perry Associates can help. With extensive experience as building surveyors in Cornwall and across the South West, we are equipped to advise you on your next project. For more information, please don’t hesitate to get in touch today.