Before we look at BATS in more detail we need a good way to classify entire bridges not just with respect to form but much more generally.
One good way is PMF - Purposes, Materials and Form.
Then we can also list bridges by many other interesting attributes such as geographical location, date of opening and span length etc.
The overall purposes P of a bridge are technical and social.
A necessary technical purpose is to carry traffic and people safely.
The social purposes and their consequences may be varied and complex - including financial and economic, aesthetic and cultural factors.
Financial purposes may include the economic regeneration of an area.
Bridges cost money to build and maintain but they also may have a direct impact on the economy of a region as new routes open up.
The financial purpose will usually be expressed as a business case.
Aesthetic purposes may include marking a significant event such as an anniversary or major exhibition.
Bridges may be ugly or eye catching. Some may even be classed be classed as public art - click here or on the Header Bridges as art for more.
Some bridges become so symbolic and iconic as major links between important parts of a city or region that they
form an important part of the whole culture of that area.
P largely determines how the bridge will be used and strongly influences its form, the materials it will be made from and how it will be erected.
For example, a bridge over navigable water must allow ships to pass - so some bridges may have to lift or swing - see Peros Lifting Bridge
in Bristol docks in the top right picture.
Transporter bridges, such as at Newport, Wales (shown right second down) carry traffic in a gondola.
Footbridges, highway bridges and railway bridges carry pedestrians, road traffic and trains.
However different structural solutions may be required for different terrain such as spanning over rivers, railways, roads or deep valleys.
The list of M for materials from which bridges are made is quite short.
It includes timber, masonry, concrete, iron, steel and more recently aluminium and plastics, but little else.
Of course since bridges sit on the ground bridge engineers must study the behaviour of engineering soils and rock
Bridge materials have to be strong enough for the job they will be asked to do, be readily available and not too expensive.
Combinations of material are used. For example, because concrete is strong when squashed but weak when pulled, steel bars are used to reinforce it.
The choice of F for the form of a bridge is one of the most critical decisions that a bridge builder has to make and that is why it tends to be
used to classify bridge types. This is where, as we shall see, BATS play their part.
First and foremost the structure must be able to stand firm whatever happens and so unsurprisingly that is a major preoccupation.
Whatever the natural or man made hazards, the bridge must be safe.
High winds, heavy rain, earthquakes and tidal waves, very heavy lorries and trucks and even terrorist attacks have to be resisted.
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Peros Lifting Bridge, Bristol Docks, England
Newport Tranporter Bridge, Wales
Clevedon Pier, England
Snowy Creek Bridge, New Zealand
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