It is a piece of infrastructure used to overcome an obstacle, whether artificial or natural, so as to ensure the continuity of a communication route. That is a general definition of a bridge, a construction that has always been fundamental for human society: after all, the greatest civilizations of the past were all built beside rivers, from the Nile to the Euphrates, and of course the Tiber, too. And the oldest bridges in the world that are still in use today include the Milvio bridge in Rome, over the Tiber. But before that bridge there were, of course, many others, built of wood before they were built of stone. And one of the main ways to distinguish between different types of bridge is, in fact, the material used: wood, stone, brick, concrete, steel or composite materials. Another way of classifying bridges would be by how they are used: so there are road bridges, for motor vehicles; pedestrian bridges for pedestrians; railway bridges for trains; and finally pipe bridges, simply for supporting pipelines.
Let’s take a look at the different types of bridge based on the obstacle they overcome, and after that, based on the type of structure.
Different types of bridges based on the obstacle they overcome
Bridges can be constructed to overcome a great variety of obstacles: indeed, based on the reason for the construction, the name of these structures changes.
The bridge: a bridge is literally a structure constructed to span a water course, whether it is a river or a mountain stream.
The viaduct: in contrast to a simple bridge, a viaduct is built to span morphological obstacles of various kinds, such as narrow valleys or gorges.
Overpass or flyover: here, the obstacle to overcome is not a natural one, but an artificial one; more specifically, if the bridge serves to pass over a road, it is called a flyover.
Overhead bridges: these may be roads or railways that are elevated in order to pass over parts of urban areas.
Types of bridge based on the structure
Let’s take a look now at the different types of bridge based on the structure, or rather their static scheme.
Girder bridges
This is currently the most common type of bridge. These bridges have girders supported horizontally on vertical piers. There are different types of girder bridge, however, such as the supported girder bridge or the continuous girder bridge; the latter makes it possible to construct larger spans, since a girder resting on several piers can automatically count on a counterweight. One famous example of a girder bridge is the Europa Brücke, between the Brenner and Innsbruck: built in 1963, it has 6 spans, the longest being 198 metres, while its tallest pier is 146.5 metres high.
Arch bridges
We no longer talk about piers so much as arches. By exploiting the mechanism of compression of construction materials, it makes it possible to achieve great results without using special materials, and thus the arch static scheme was extremely widespread in ancient times. This type of bridge is built using a centring so that the ashlar masonry, whether dry or with mortar, can be put in place until the last stone piece is positioned. There are round-arch bridges, such as the Roman bridges, or the more efficient segmental-arch bridges, such as the Rialto Bridge in Venice. We should add that in modern times arch bridges have been built of metal or reinforced concrete.
Rigid frame bridges
Rigid frame bridges are very distinctive structures, which exploit the typical characteristics of girder bridges and arch bridges depending on the situation. These structures are particularly suitable for prefabrication.
Cable-stayed bridges
This type of bridge is immediately recognizable through the use of stays, or inclined cables that have the task of supporting and stabilising the bridge. A commonly used alternative to suspension bridges, the subject of the next paragraph, cable-stayed bridges make it possible to cover large distances. Everything is based on the stays, in fact, these inclined cables that are anchored at one end of the pier so as to directly support the girder. The first examples of cable-stayed bridges date back to the 17th century, although the popularity and widespread use of this design has increased significantly over recent decades. Some examples of cable-stayed bridges are the Calatrava bridges in Reggio Emilia on the A1 Motorway or, looking further afield, the Russky Bridge in Vladivostok, that has held the world record among cable-stayed bridges since 2012 for the longest clear span, with a central span of 1,104 metres.
Suspension bridges
Suspension bridges also have cables, usually supported by towers located at the two ends of the bridge, or else by piers. With these bridges, however, the concept is quite different from cable-stayed bridges: the suspension bridge can be seen as an upside down arch bridge. Everything is held together by large parallel steel cables that support the lower deck, through vertical suspender hangers, also made of steel. The typical suspension bridge has three spans: one large central span and two side spans; as regards the side spans, the cables can be anchored at the ends of the girder or directly into the ground, with appropriately located structures. In the past, the suspension bridge was only used as a pedestrian route, whereas nowadays it is one of the alternatives most frequently considered for large-span road and railway crossings.
Mobile bridges
Mobile bridges are distinguished not so much by their static scheme as by the existence of the mobile part itself, which is constructed to allow navigation to continue in the water below. There are many widely-varying types of mobile bridge. The most basic examples are bridges that can be dismantled, for use during emergencies by civil engineers or armies; then there are bascule bridges, which are bridges equipped with a hinged span that can be folded or tilted up, and a counterweight; drawbridges, where a span can be raised using cables; and finally lift bridges and swing bridges.
