Log bridge

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Log bridge
Footpath bridge in the French Alps near Vallorcine
Footpath bridge in the French Alps near Vallorcine
Ancestor Step-stone bridge
Related Clapper bridge
Descendant Beam bridge
Carries Pedestrians, vehicles (on multiple parallel logs)
Span range Short
Material Logs, dry set stonework footings, top may be flattened or boards added, topped with rammed earth for vehicles
Movable No
Design effort Low
Falsework required No

A log bridge is a bridge that uses logs[1] that fall naturally or are intentionally felled or placed across streams. The first manmade bridges with significant span were probably intentionally felled trees.[2] 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[3] due to soil contact and subsequent rot and wood-eating insect infestation. Longer lasting log bridges may be constructed by using treated logs and/or by providing well drained footings[4] of stone or concrete combined with regular maintenance to prevent soil infiltration. This care in construction can be seen in the bridge illustrated, which has well locked dry set stone abutments and a footpath leveled with boards.

Complex Tibetan log bridge, approximately 50 km southeast from Tingri Shekar.

References[edit]

  1. ^ National Parks Conference, Department of the Interior (1915). Proceedings of the National parks conference held at Berkeley, California March 11, 12, and 13, 1915. Washington: Government Printing Office. p. 60. Retrieved March 14, 2010. "(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." 
  2. ^ Bennett, David (2000). "The history and development of bridges". In Ryall, M. J.; Parke, G.A.R.; Harding, J.E. The manual of bridge engineering (Google books). London: Thomas Telford. p. 1. ISBN 978-0-7277-2774-9. Retrieved March 14, 2010. 
  3. ^ National Parks Conference 1915, p. 59. "The chief objection to a log bridge ... is the shortness of its life."
  4. ^ 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."