Beam bridges are the simplest structural forms for bridge spans supported by an abutment or

pier Seaside pleasure pier in England.html" ;"title="Brighton, England">Brighton, England. The first seaside piers were built in England in the early 19th century. A pier is a raised structure that rises above a body of water and usually juts out ...

at each end. No moments are transferred throughout the support, hence their structural type is known as ''

simply supported Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and muscles' that create the form and shape of man-made structures. Structural engineers also must understand and cal ...

''. The simplest beam bridge could be a log (see

log bridge A log bridge is a timber bridge that uses logs that fall naturally or are intentionally felled or placed across streams. The first man-made bridges with significant span were probably intentionally felled trees. The use of emplaced logs is now ...

), a wood plank, or a stone slab (see

clapper bridge A clapper bridge is an ancient form of bridge found on the moors of the English West Country ( Bodmin Moor, Dartmoor and Exmoor) and in other upland areas of the United Kingdom including Snowdonia and Anglesey, Cumbria, Derbyshire, Yorkshire ...

) laid across a stream. Bridges designed for modern infrastructure will usually be constructed of steel or reinforced concrete, or a combination of both. The concrete elements may be reinforced, prestressed or post-tensioned. Such modern bridges include girder, plate girder, and box girder bridges, all types of beam bridges. Types of construction could include having many beams side by side with a deck across the top of them, to a main beam either side supporting a deck between them. The main beams could be I-beams,

truss A truss is an assembly of ''members'' such as beams, connected by ''nodes'', that creates a rigid structure. In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assembla ...

es, or box girders. They could be half-through, or braced across the top to create a through bridge. Passerelle ruisseau Moulin-Haut

Because no moments are transferred,

thrust Thrust is a reaction force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can al ...

(as from an

arch bridge An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side. A viaduct (a ...

) cannot be accommodated, leading to innovative designs, such as lenticular trusses and

bow string arch A tied-arch bridge is an arch bridge in which the outward horizontal forces of the arch(es) caused by tension at the arch ends to a foundation are countered by equal tension of its own gravity plus any element of the total deck structure such grea ...

es, which contain the

horizontal Horizontal may refer to: *Horizontal plane, in astronomy, geography, geometry and other sciences and contexts *Horizontal coordinate system, in astronomy *Horizontalism, in monetary circuit theory *Horizontalism, in sociology *Horizontal market, ...

forces within the superstructure. Beam bridges are not limited to a single

span Span may refer to: Science, technology and engineering * Span (unit), the width of a human hand * Span (engineering), a section between two intermediate supports * Wingspan, the distance between the wingtips of a bird or aircraft * Sorbitan es ...

. Some

viaduct A viaduct is a specific type of bridge that consists of a series of arches, piers or columns supporting a long elevated railway or road. Typically a viaduct connects two points of roughly equal elevation, allowing direct overpass across a wide va ...

s such as the

Feiyunjiang Bridge Feiyunjiang Bridge is a bridge in Rui'an, Zhejiang Zhejiang ( or , ; , also romanized as Chekiang) is an eastern, coastal province of the People's Republic of China. Its capital and largest city is Hangzhou, and other notable cities incl ...

in China have multiple simply supported spans supported by piers. This is opposed to viaducts using continuous spans over the piers. Beam bridges are often only used for relatively short distances because, unlike truss bridges, they have no built in supports. The only supports are provided by piers. The farther apart its supports, the weaker a beam bridge gets. As a result, beam bridges rarely span more than . This does not mean that beam bridges are not used to cross great distances; it only means that a series of beam bridges must be joined together, creating what is known as a continuous span.

References

{{Bridge footer Bridges by structural type