Science Fair Project Encyclopedia
The Bailey bridge is a portable pre-fabricated truss bridge, designed for use by military engineering units to bridge up to 60 m (200 foot) gaps. It requires no special tools or heavy equipment for construction, the bridge elements are small enough to be carried in trucks, and the bridge is strong enough to carry tanks. It is considered one of the great examples of military engineering.
Donald Bailey was a civil servant in the British War Office who tinkered with model bridges as a hobby. He presented one such model to his chiefs, who saw some merit in the design and had construction started at a slow rate. A number of bridges were available by 1944 for D-Day, when production was ramped up. The US also licensed the design and started rapid construction for their own use. Bailey was later knighted for his invention, which continues to be widely produced and used today.
The original design however, violated a patent on the Hamilton-Callender bridge . The designer of that bridge, A. M. Hamilton successfully applied to the Royal Commission for Awards to Inventors . The Bailey bridge had however several advantages over Hamilton's design.
A large part of what made Bailey bridges as successful and unique as they were is the modular design, and the fact that it could be assembled with minimal aid from heavy machinery. Most, if not all, previous designs for military bridges required cranes to lift up the preassembled bridge and lower it into place. The Bailey's parts were made of standard steel alloys, and were simple enough that parts made at a number of different factories could be completely interchangeable. And each individual part could be carried by a small number of men, enabling army engineers to move more easily and more quickly than before, in paving the way for their comrades advancing behind them. Finally, the modular design allowed engineers to build each bridge to be as long and as strong as they needed it, doubling up on the supportive side panels, or on the roadbed sections.
The basic bridge consists of three main parts. The "floor" of the bridge consists of a number of 19 foot wide transoms that run across the bridge, with 10 foot long stringers running between them on the bottom, forming a square. The bridge's strength is provided by the panels on the sides, which are 10 foot long cross-braced rectangles. These are placed standing upright above the stringers, and clamps run from the stringers to the panels to hold them together. Ribands are placed on top of the completed structural frame, and wood is placed on top of the ribands to provide a roadbed. Later in the war, these wooden panels were replaced by steel, which was more resistant to the damage wrought by tank treads.
Each unit constructed in this fashion creates a single 10 foot long section of bridge, with a 12 foot wide 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 several panels (and transoms) can be bolted on either side of the bridge, up to three. Another solution is to stack the panels vertically. With three panels across and two high, the Bailey Bridge can support tanks over a 200 foot span with no additional supports in the middle.
An astonishing feature of the Bailey bridge is its ability to be "launched" from one side of a gap. In this system the frontmost portion of the bridge is angled up with wedges into 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, 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.
Stories of Bailey bridges being built and erected during the Second World War are legendary. In one instance a bridge was pushed over the Saar River while under artillery and tank fire. When the enemy was finally cleared out the panels had holes in them and would not carry the weight of a tank. Replacing the panels would require the bridge to be "broken" in the middle. Instead they simply bolted an entirely new set of panels onto the bridge on top of the original set, a technique that later became a standard feature.
The Bailey provided an excellent solution to the problem of German and Italian armies destroying bridges as they retreated. By the end of the war, the US Fifth and British Eight armies built over 3,000 Baileys in Sicily and Italy alone, totaling over 55 miles of bridge, at an average length of 100 feet. One Bailey, built to replace the Sangro River bridge in Italy, spanned 1,126 feet.
- McLaughlin, Mike (May 2005). "The practical and portable British Bailey Bridge helped Allied troops remain on the march." Military Heritage Presents: WWII History, pp. 10-15, 76.
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