Beam bridge

{{Short description|Type of bridge}} {{Multiple issues| {{more citations needed|date=December 2019}} {{disputed|date=September 2018}} }} {{Use dmy dates|date=June 2017}}

{{Infobox bridge type |type_name = Beam bridge |image = SteamAcrossIowaRiver.JPG |image_title = Multispan plate girder bridge deck on concrete piers. |sibling_names = |descendent_names = Box girder bridge, plate girder bridge, trestle bridge, truss bridge{{citation needed|reason=please provide a reference which defines or lists siblings, descendants, and ancestors for bridge types. |date=January 2011}} |ancestor_names = Log bridge{{cn|date=April 2026}} |carries = Pedestrians, automobiles, trucks, light rail, heavy rail |span_range = Short |material = Timber, iron, steel, reinforced concrete, prestressed concrete |movable = No |design = Low |falsework = No unless cast-in-place reinforced concrete is used }} [[File:Drvenija most nizvodno 24022014377.jpg|thumb|Drvenija bridge, Sarajevo]] '''Beam bridges''' are the simplest structural forms for bridge spans supported by an abutment or pier at each end.<ref name=":0">{{cite web |url=https://www.historyofbridges.com/facts-about-bridges/beam-bridge/ |title=Beam Bridge Facts, History and Design |author= |website=History of bridges |access-date=2019-09-13 }}</ref> 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 wood plank, or a stone slab (see clapper bridge) 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 or prestressed. Such modern bridges include girder, plate girder, and box girder bridges, all of which are types of beam bridges.

Types of construction could include having many beams side by side with a deck across the top of them, or a main beam on either side supporting a deck between them. The main beams could be I-beams, trusses, or box girders. They could be half-through, or braced across the top to create a through bridge.

Since no moments are transferred, thrust (as from an arch bridge) cannot be accommodated, leading to innovative designs, such as lenticular trusses and bow string arches, which contain the horizontal forces within the superstructure.

Beam bridges are not limited to a single span. Some viaducts, such as the Feiyunjiang Bridge in China, have multiple supported spans held up by piers. This is in contrast to viaducts that use 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. Piers provide the only support. The further apart its supports, the weaker a beam bridge gets. As a result, beam bridges rarely span more than {{convert|250|ft|-1}}. This does not mean that beam bridges are not used to span great distances; it only means that a series of beam bridges must be joined, creating what is known as a continuous span.

== History == The beam bridges are amoung the earliest forms of bridges constructed by humans, originating as imitations of natural formations. Prehistoric people observed fallen trees spanning streams and replicated this approach in locations where it was practical. <ref name=":0" />

==References== {{Commons}} {{Reflist}}

Category:Beam bridges Category:Bridges by structural type Category:Civil engineering Category:Structural engineering