Beam bridges are the simplest structural forms for bridge spans 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 that provide vertical and lateral support for the span, as well as acting as retaining walls ...

pier A pier is a raised structure that rises above a body of water and usually juts out from its shore, typically supported by piling, piles or column, pillars, and provides above-water access to offshore areas. Frequent pier uses include fishing, b ...

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 (see clapper bridge) laid across a stream. Bridges designed for modern

infrastructure Infrastructure is the set of facilities and systems that serve a country, city, or other area, and encompasses the services and facilities necessary for its economy, households and firms to function. Infrastructure is composed of public and pri ...

will usually be constructed of

steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...

reinforced concrete Reinforced concrete, also called ferroconcrete or ferro-concrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having higher tensile strength or ...

, or a combination of both. The concrete elements may be reinforced or

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 is ...

. Such modern bridges include

girder A girder () is a Beam (structure), 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 sta ...

, 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-beam An I-beam is any of various structural members with an - (serif capital letter 'I') or H-shaped cross section (geometry), cross-section. Technical terms for similar items include H-beam, I-profile, universal column (UC), w-beam (for "wide flang ...

truss A truss is an assembly of ''members'' such as Beam (structure), 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 ...

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

Since 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 ...

(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 structural load, loads partially into a horizontal thrust restrained by the abutments at either si ...

) cannot be accommodated, leading to innovative designs, such as lenticular trusses and bow string arches, which contain the horizontal forces within the

superstructure A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships. Aboard ships and large boats On water craft, the superstruct ...

. Beam bridges are not limited to a single span. 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 ...

s such as the Feiyunjiang Bridge in China have multiple simply supported spans held up 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 further 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