# Arch Bridges

## What is the basic structure of the bridge and what makes it unique?

An arch bridge is a bridge that is built with an arch base or a bridge fitted with an arch on top, such as the Sydney Harbour Bridge. It is unique because it`s the only bridge that utilizes an arch and it often contains a keystone ( which is shaped like an upside down trapezium) and because the force pushing on the bridge can`t keep pushing down it has to spread out to the abutments( the abutments are the bottom piece of the arch supporting the bridge. This is why arch bridges are often very hard to collaspe.

## When and where was it first used?

It was first used over 2000 years ago by the Ancient Greeks but was very popular in the Roman Empire. Almost 2000 arch bridges each year were constructed in the Roman Empire.

## Give a famous example of this type of bridge and explain why this type of bridge was chosen for that particular place.

A famous example of the arch bridge is Stari Most, a bridge located in Bosnia( a country located in Central Europe). It connects two cities together and was chosen for this particular place because the two cities are separated by a narrow river so since an arch bridge can be built in any different sizes it`s the perfect bridge for this location.

## What materials is it commonly made out of?

Before the Industrial Revolution( in the middle 19th century) most arch bridges were constructed by stone. Nowadays, many arch bridges are built by steel and hard metals. Stone Arch Bridges are the most common arch bridges, having at least 65,000 stone arch bridges worldwide.( There are approximately 14,000 steel arch bridges.)

## Are there any limitations with this particular bridge design?

There are a few limitations to this design. The main problem is calculating the very exact measurements required to successfully construct this shape. Nowadays, many arch bridges are constructed with the help of technology and computers. Imagine how the Romans and Greeks were able to build an arch bridge without machinery! They would of have to use mathematics to find the exact angle and measurements of this shape. Well, the Romans built many arch bridges all over their empire. But in the amount of time it took them to make a single arch was approximately a month! Also, the wider the arch the weaker it is, since the abutments would be far away from each other and the middle would have nothing underneath it to support it, meaning that it would be easier to build a bunch of small arches instead, like the bridge in the picture below.