Warren truss

Warren truss illustrated – some of the diagonals are under compression and some under tension

A Warren truss or equilateral truss[1] is a type of engineering truss.

Wills Creek Bollman Bridge, a short Warren truss bridge of 1871

Origins

It was patented in 1848 by its designers James Warren and Willoughby Theobald Monzani.

Truss

The Warren truss consists of longitudinal members joined only by angled cross-members, forming alternately inverted equilateral triangle-shaped spaces along its length. This gives a pure truss: each individual strut, beam, or tie is only subject to tension or compression forces, there are no bending or torsional forces on them.

Loads on the diagonals alternate between compression and tension (approaching the centre), with no vertical elements, while elements near the centre must support both tension and compression in response to live loads. This configuration combines strength with economy of materials and can therefore be relatively light. The girders being of equal length, it is ideal for use in prefabricated modular bridges.

It is an improvement over the Neville truss which uses a spacing configuration of isosceles triangles.[2]

A variant of the Warren truss has additional vertical members within the triangles.[1] These are used when the lengths of the upper horizontal members would otherwise become so long at to present a risk of buckling[lower-roman 1] These verticals do not carry a large proportion of the truss loads, they act mostly to stabilise the horizontal members against buckling.

Bridges

Crumlin Viaduct,[3] 1857, an important early use of the Warren truss[4]
Chiba Urban Monorail, Japan

Architecture

The Warren truss is also a prominent structural feature in hundreds of hastily constructed aircraft hangars in WW2. In the early parts of the war, the British and Canadian government formed an agreement known as the British Commonwealth Air Training Plan which used newly constructed airbases in Canada to train aircrew needed to sustain emerging air forces. Dozens and hundreds of airfields, aprons, taxiways and ground installations were constructed all across Canada. Two characteristic features were, and indeed many still remain in service, are a triangle runway layout and hangars built from virgin British Columbia timbers with Warren truss configuration roofs.[5][6]

Aircraft

Museum model of the 1914 Zeppelin-Lindau Rs.I flying boat, with spanwise Warren-truss "inverted-pyramid" interplane struts
A preserved original Ansaldo SVA aircraft, showing the Warren truss-pattern spanwise interplane wing strut layout

Warren truss construction has also been used in airframe construction for aircraft since the 1920s, mostly for smaller aircraft fuselages, using chrome molybdenum alloy steel tubing, with popular aircraft such as the Piper J-3 Cub. Two of the earliest uses for the Warren truss in aircraft design was for both the 1914-era, Zeppelin-Lindau Rs.I biplane flying boat designed by Claudius Dornier, with four "inverted-pyramid" structures per side for its interplane struts, giving it Warren trusses running in both spanwise and chordwise directions—and by 1916–17, the interplane wing strut layout, as seen in a nose-on view, on the Italian World War I Ansaldo SVA series of fast reconnaissance biplanes, which were among the fastest aircraft of the First World War era. Warren truss construction is still used today for some homebuilt aircraft fuselage designs, that essentially use the same 1920s-era design philosophies in the 21st century.

References

  1. ↑ Column theory shows that the risk of buckling increases with length, not merely compressive load.
  1. 1 2 Frank Griggs, Jr. (July 2015). "The Warren Truss". Structure.
  2. ↑ "Warren Truss". Garrett's Bridges.
  3. ↑ Jones, Stephen K. (2009). Brunel in South Wales. III: Links with Leviathans. Stroud: The History Press. pp. 20–21. ISBN 9780752449128.
  4. ↑ de Maré, Eric (1975) [1954]. Bridges of Britain. Batsford. pp. 86–87. ISBN 0-7134-2925-9.
  5. ↑ "HistoricPlaces.ca - HistoricPlaces.ca".
  6. ↑ Rkelland (10 February 2016). "Hangar 14 and the British Commonwealth Air Training Plan".
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