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A type of bridge girder.
The longitudinal members are connected only by angled cross-members, forming a series of inverted equilateral triangles along the length of the girder. The structure is statically determinate.
A variant of the Warren truss has additional vertical members within the triangles. These are used when the lengths of the upper horizontal members would otherwise become so long at to present a risk of buckling. The verticals do not carry a large proportion of the truss loads, they act mainly to stabilise the horizontal members against buckling.
See Wikipedia entry.
The truss was patented. Patent applied for on 15 August 1848, James Warren and Willoughby Theobald Monzani, and enrolled on 15 February 1849 (No. 12,242) and became known as the Warren truss. Its first major application on a railway was to carry the GNR main line over a branch of the Trent at Newark. The second important use of the Warren truss was in the Crumlin Viaduct.