Introduction to Bridge Building

A look at the history and structuring of bridges

/brij/- a structure carrying a road, path, railroad, or canal across a river, ravine, road, railroad, or other obstacle.

Bridges were originally developed by nature— a tree falling down across a river, stones making a stepping-stone pathway across a shallow stream.

The first man-made bridges came from these natural bridges, and were called clapper bridges.

Ancient Rome

Ancient Romans refined and modernized bridge building by using two techniques. Almost all of their bridges were designed with

arches, which can support more weight than a flat bridge.

They also discovered a natural form of cement, allowing their bridges to be stronger and longer lasting.

Asia

Some builders used a cantilever design, which made it easier to build over wide rivers.

The Great Stone Bridge used an arch design, though not the same design as the Romans used.

Modern cantilever bridge made from steel

Modern Bridges

About 200 years ago, the first bridge made from cast-iron was built. From there, wrought iron was used, and then

steel. Many new bridge types were tested and

improved during this time, such as the truss and suspension bridge.

Basic Types of Bridges

Beam bridges, arch bridges, and suspension bridges

Beam Bridges

Beam bridges are flat across and are supported at the two ends. Depending on length, there might be supports in the middle.

The weight of the bridge, and the weight of what it carries, are downward forces on the bridge. The downward force is then spread evenly through the length of the bridge.

Arch Bridges

Arch bridges go across the river in an arched shape, rather than flat across.

This enables the downwards force on the bridge be pushed outwards, towards the two ends of the bridge.

Suspension Bridges

Suspension bridges droop down between two ends which hold it up. Modern suspension bridges have towers to help support cables.

The droop of the bridge causes the downwards pressure to go inwards.