Editing Bailey bridge (section)

== Design ==
[[File:Bailey_bridge_element,_Ranville_01_09.jpg|right|thumb|upright=1.4|The transoms, side-panels and stringers of a Bailey bridge section at the [[Memorial Pegasus]] museum in [[Ranville]], Calvados, France, can all be clearly seen]]{{More citations needed section|date=November 2018}}[[File:The_British_Army_in_Italy_1943_NA7082.jpg|right|thumb|upright=1.4|[[Royal Engineers]] construct a Bailey bridge in Italy, September 1943. Wood planks are being laid over the stringers to construct the roadbed]]
The success of the Bailey bridge was due to the simplicity of the fabrication and assembly of its modular components, combined with the ability to erect and deploy sections with a minimum of assistance from [[heavy equipment]]. Many previous designs for military bridges required [[Crane (machine)|cranes]] to lift the pre-assembled bridge and lower it into place. The Bailey parts were made of standard [[steel]] [[alloy]]s, and were simple enough that parts made at a number of different factories were interchangeable. Each individual part could be carried by a small number of men, enabling army engineers to move more easily and quickly, in preparing the way for troops and [[materiel]] advancing behind them. The modular design allowed engineers to build each bridge to be as long and as strong as needed, doubling or tripling the supportive side panels, or on the roadbed sections.<ref>{{cite web |url=http://www.mabeybridge.com/modular-bridging/history-of-the-bailey-bridge/ |title=The Story of the Bailey Bridge |work=Mabey Bridge |publisher=Mabey Bridge Ltd. |archive-url=https://web.archive.org/web/20151031050012/http://www.mabeybridge.com/modular-bridging/history-of-the-bailey-bridge/ |access-date=3 October 2015|archive-date=2015-10-31 }}</ref>

The basic bridge consists of three main parts. The bridge's strength is provided by the panels on the sides. The panels are {{convert|10|ft|m|-long|adj=mid}}, {{convert|5|ft|m|-high|adj=mid}}, cross-braced rectangles that each weigh {{convert|570|lb|kg}}, and can be lifted by four men. The panel was constructed of welded steel. The top and bottom chord of each panel had interlocking male and female lugs into which engineers could insert panel connecting pins.<ref name="thinkdefence">{{cite web |url=http://www.thinkdefence.co.uk/2012/01/uk-military-bridging-equipment-the-bailey-bridge/ |title=UK Military Bridging – Equipment (The Bailey Bridge) |work=Think Defence |date=8 January 2012 |publisher=ThinkDefence |access-date=28 March 2015}}</ref>

The floor of the bridge consists of a number of {{convert|19|ft|m|-wide|adj=mid}} [[Transom (architecture)|transoms]] that run across the bridge, with {{convert|10|ft|m|-long|adj=mid}} stringers running between them, and over the top of the transoms, forming a square.<ref name="launching">{{cite journal |date=7 October 1943 |title=Launching the Bailey Bridge |url=http://www.lonesentry.com/articles/ttt07/bailey-bridge.html |journal=Tactical and Technical Trends |issue=35 |access-date=2011-09-11}}</ref> Transoms rest on the lower chord of the panels, and clamps hold them together. Stringers are placed atop the completed structural frame, and [[wood plank]]ing (chesses) are placed atop the stringers to provide a roadbed. Ribands bolt the planking to the stringers. Later in the war, the wooden planking was covered by steel plates, which were more resistant to damage from [[tank track]]s.

Each unit constructed in this fashion creates a single {{convert|10|ft|m|-long|adj=mid}} section of bridge, with a {{convert|12|ft|m|-wide|adj=mid}} roadbed. After one section is complete it is typically pushed forward over rollers on the bridgehead, and another section built behind it. The two are then connected together with pins pounded into holes in the corners of the panels.

For added strength up to three panels (and transoms) can be bolted on either side of the bridge. Another solution is to stack the panels vertically. With three panels across and two high, the Bailey Bridge can support tanks over a {{convert|200|ft|m|[[Span (architecture)|span]]|adj=mid}}. Footways can be installed on the outside of the side-panels. The side-panels form an effective barrier between foot and vehicle traffic, allowing pedestrians to safely use the bridge.<ref name="warillustrated" />

A useful feature of the Bailey bridge is its ability to be launched from one side of a gap, without a need for any equipment or personnel on the far bank.<ref name="launching" /> In this system the front-most portion of the bridge is angled up with short "launch-links" to form a "launching nose" and most of the bridge is left without the roadbed and ribands. The bridge is placed on rollers and simply pushed across the gap, using manpower or a truck or tracked vehicle, at which point the roller is removed (with the help of jacks) and the ribands and roadbed installed, along with any additional panels and transoms that might be needed.

During WWII, Bailey bridge parts were made by companies with little experience of this kind of engineering. Although the parts were simple, they had to be precisely manufactured to fit correctly, so they were assembled into a test jig at each factory to verify this. To do this efficiently, newly manufactured parts would be continuously added to the test bridge, while at the same time the far end of the test bridge was continuously dismantled and the parts dispatched to the end-users.<ref name="warillustrated" />