Editing Pontoon bridge (section)

==Design==
[[File:The longest pontoon bridge in the world, spanning Russellville and Dardanelle, Arkansas. - NARA - 516537.tif|thumb|[[Dardanelle pontoon bridge|Pontoon bridge]] between [[Russellville, Arkansas|Russellville]] and [[Dardanelle, Arkansas|Dardanelle]], [[Arkansas]], US, at the time reportedly the longest pontoon bridge in the world.<ref>{{cite web |title=The longest pontoon bridge in the world, spanning Russellville and Dardanelle, Arkansas. |url=https://catalog.archives.gov/id/516537 |website=National Archive catalog |publisher=U.S. National Archives and Records Administration |access-date=2 March 2023}}</ref> (Photo {{circa|1913–1926}})]]
[[File:Bergsøysundbrua.jpg|thumb|The [[Bergsøysund Bridge]] uses concrete pontoons]]
When designing a pontoon bridge, the [[civil engineer]] must take into consideration [[Archimedes' principle]]: Each pontoon can support a load equal to the mass of the water that it [[displacement (fluid)|displaces]]. This [[structural load|load]] includes the mass of the bridge and the pontoon itself. If the maximum load of a bridge section is exceeded, one or more pontoons become submerged. Flexible connections have to allow for one section of the bridge to be weighted down more heavily than the other parts. The roadway across the pontoons should be relatively light, so as not to limit the carrying capacity of the pontoons.<ref>{{cite web |url=http://physics.weber.edu/carroll/archimedes/principle.htm |title=Archimedes' Principle |access-date=2015-10-22 |archive-date=2007-08-08 |archive-url=https://web.archive.org/web/20070808132323/http://physics.weber.edu/carroll/Archimedes/principle.htm |url-status=live }}</ref>

The connection of the bridge to shore requires the design of approaches<ref>{{cite web|url=http://science.howstuffworks.com/engineering/structural/floating-bridge3.htm|title=Making the Critical Connections|date=13 September 2011|access-date=22 October 2015|archive-date=22 November 2015|archive-url=https://web.archive.org/web/20151122032130/http://science.howstuffworks.com/engineering/structural/floating-bridge3.htm|url-status=live}}</ref> that are not too steep, protect the bank from erosion and provide for movements of the bridge during (tidal) changes of the water level.

Floating bridges were historically constructed using wood. Pontoons were formed by simply lashing several barrels together, by rafts of timbers, or by using boats. Each bridge section consisted of one or more pontoons, which were maneuvered into position and then anchored underwater or on land. The pontoons were linked together using wooden [[stringer (aircraft)|stringer]]s called ''balks''. The balks were covered by a series of cross planks called ''chesses'' to form the road surface,<ref>{{cite book |last=de Tousard |first=Louis |title=American Artillerist's Companion: Or Elements of Artillery. Treating of All ... |page=424}}</ref> and the chesses were secured with side [[guard rail]]s.

A floating bridge can be built in a series of sections, starting from an anchored point on the shore. Modern pontoon bridges usually use pre-fabricated floating structures.<ref>{{cite web |url=http://www.fs.fed.us/t-d/pubs/pdfpubs/pdf02232812/pdf02232812dpi72.pdf |title=Floating Trail Bridges and Docks |access-date=2015-10-22 |archive-date=2017-05-19 |archive-url=https://web.archive.org/web/20170519061550/https://www.fs.fed.us/t-d/pubs/pdfpubs/pdf02232812/pdf02232812dpi72.pdf |url-status=live }}</ref>

Most pontoon bridges are designed for temporary use, but bridges across water bodies with a constant water level can remain in place much longer. [[Hobart Bridge]], a long pontoon bridge built 1943 in [[Hobart]], [[Tasmania]] was only replaced after 21 years.<ref>{{cite web|url=http://www.abc.net.au/news/2015-05-05/hobart-floating-bridge-declared-national-heritage-marker/6446520|title=Historic Hobart floating bridge declared National Engineering Heritage Landmark|website=[[Australian Broadcasting Corporation]]|date=5 May 2015|access-date=2015-10-22|archive-date=2015-10-31|archive-url=https://web.archive.org/web/20151031175405/http://www.abc.net.au/news/2015-05-05/hobart-floating-bridge-declared-national-heritage-marker/6446520|url-status=live}}</ref> The fourth [[Galata Bridge]] that spans the [[Golden Horn]] in [[Istanbul]], [[Turkey]] was built in 1912 and operated for 80 years.

Provisional and lightweight pontoon bridges are easily damaged. The bridge can be dislodged or inundated when the load limit of the bridge is exceeded. The bridge can be induced to sway or [[oscillate]] in a hazardous manner from the swell, from a storm, a flood or a fast moving load. Ice or floating objects ([[flotsam]]) can accumulate on the pontoons, increasing the drag from river current and potentially damaging the bridge. See below for floating pontoon failures and disasters.