Beam bridges are the simplest structural forms for

bridge span Span is the distance between two intermediate supports for a structure, e.g. a beam or a bridge. A span can be closed by a solid beam or by a rope. The first kind is used for bridges, the second one for power lines, overhead telecommunication line ...

s supported by an

abutment An abutment is the substructure at the ends of a bridge span or dam supporting its superstructure. Single-span bridges have abutments at each end which provide vertical and lateral support for the span, as well as acting as retaining walls ...

pier Seaside pleasure pier in Brighton, England. The first seaside piers were built in England in the early 19th century.">England.html" ;"title="Brighton, England">Brighton, England. The first seaside piers were built in England in the early 19th ...

at each end. No moments are transferred throughout the support, hence their structural type is known as '' simply supported''. 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 In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition, and the way in which it is formed. Rocks ...

slab Slab or SLAB may refer to: Physical materials * Concrete slab, a flat concrete plate used in construction * Stone slab, a flat stone used in construction * Slab (casting), a length of metal * Slab (geology), that portion of a tectonic plate tha ...

(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, La ...

) 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 Prestressed concrete is a form of concrete used in construction. It is substantially "prestressed" ( compressed) during production, in a manner that strengthens it against tensile forces which will exist when in service. Post-tensioned concreted i ...

or post-tensioned. Such modern bridges include

girder A girder () is a support beam used in construction. It is the main horizontal support of a structure which supports smaller beams. Girders often have an I-beam cross section composed of two load-bearing ''flanges'' separated by a stabilizing ...

plate girder A plate girder bridge is a bridge supported by two or more plate girders. Overview In a plate girder bridge, the plate girders are typically I-beams made up from separate structural steel plates (rather than rolled as a single cross-section), ...

, and box girder bridges, all types of beam bridges. Types of construction could include having many

beam Beam may refer to: Streams of particles or energy *Light beam, or beam of light, a directional projection of light energy **Laser beam *Particle beam, a stream of charged or neutral particles **Charged particle beam, a spatially localized grou ...

s 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-beam An I-beam, also known as H-beam (for universal column, UC), w-beam (for "wide flange"), universal beam (UB), rolled steel joist (RSJ), or double-T (especially in Polish, Bulgarian, Spanish, Italian and German), is a beam with an or -shape ...

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 assembl ...

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 described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that sys ...

(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 ...

) cannot be accommodated, leading to innovative designs, such as

lenticular 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 assembl ...

es and bow string arches, which contain the horizontal 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 ester ...

. Some viaducts such as the Feiyunjiang Bridge 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

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