Editing Log bridge (section)

{{short description|Bridge that uses logs that fall naturally or are intentionally felled or placed across streams}}
<!-- this taxobox is for generic bridge types, not specific (except as an example). The ancestor, sibling, and descendant references should follow the current taxonomy at media:BridgeTaxonomy.jpg, see also Talk:Bridge -->
{{BridgeTypePix|
|type_name        = Log bridge
|image            = Passerelle sommaire sur l'Alzou en crue.jpg
|image_title      = Simple log bridge over the [[Alzou (Ouysse)|Alzou]] in France
|sibling_names     = [[Clapper bridge]]
|descendant_names = [[Beam bridge]]
|ancestor_names   = [[Step-stone bridge]]
|carries          = [[Pedestrian]]s, [[vehicle]]s (on multiple parallel logs)
|span_range       = Short
|material         = [[Logging|Logs]], dry set stonework footings, top may be flattened or boards added, topped with rammed earth for vehicles
|movable          = No
|design           = Low
|falsework        = No
|}}
A '''log bridge''' is a [[timber bridge]] that uses logs<ref>{{cite book | last=National Parks Conference| first= Department of the Interior| title=Proceedings of the National parks conference held at Berkeley, California March 11, 12, and 13, 1915| url=https://archive.org/details/proceedingsnati01confgoog| access-date=March 14, 2010| year=1915| publisher=[[United States Government Publishing Office|Government Printing Office]]| location=Washington| page=[https://archive.org/details/proceedingsnati01confgoog/page/n443 60]| quote=(A log bridge) is a bridge composed of log beams, the logs being in natural condition or hewn, which are thrown across two abutments, and over which traffic may pass.| ref=NPC}}</ref> that fall naturally or are intentionally felled or placed across streams. The first man-made [[bridge]]s with significant span were probably intentionally felled [[tree]]s.<ref>{{cite book |last1=Bennett| first1=David| editor1-first=M. J.| editor1-last=Ryall| editor2-first=G.A.R.| editor2-last=Parke| editor3-first=J.E.| editor3-last=Harding| title=The manual of bridge engineering| url=https://books.google.com/books?id=8PGk81gtCywC| format=Google books| access-date=March 14, 2010| year=2000| publisher=Thomas Telford| location=London| isbn=978-0-7277-2774-9| page=1| chapter=The history and development of bridges| chapter-url=https://books.google.com/books?id=8PGk81gtCywC&pg=PA1}}</ref> 

The use of emplaced logs is now sometimes used in temporary bridges used for [[logging]] roads, where a forest tract is to be harvested and the road then abandoned. Such log bridges have a severely limited lifetime<ref>[[#NPC|National Parks Conference 1915]], p. 59. "The chief objection to a log bridge ... is the shortness of its life."</ref> due to [[soil]] contact and subsequent rot and [[Xylophagy|wood-eating]] [[insect]] infestation. 

Longer lasting log bridges may be constructed by using treated logs and/or by providing well drained [[Foundation (engineering)|footings]]<ref>[[#NPC|National Parks Conference 1915]], p. 59. "If we can design the abutment so that no moisture can collect under the logs the life of the bridge is materially increased."</ref> of [[Rock (geology)|stone]] or [[concrete]] combined with regular maintenance to prevent soil infiltration. This care in construction can be seen in the French bridge illustrated below, which has well locked [[Masonry#Dry set masonry|dry set]] stone [[abutment]]s and a footpath leveled with boards.