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A truss, or lattice structure, is a structural assembly of
smallinterconnected elements.
Trusses are formed by an interconnected assembly of
relativelysmall elements, which create a lattice arrangement. The
overall form,size and shape of the truss is as important as the
strength of theindividual components, and a wide variety of design
options isavailable.
A truss acts like a beam, with bending resisted by the couple
createdby forces in the top and bottom members.
When an I-shaped beam is subjected to simple bending it can
beseen that the bulk of resistance to bending moment is offered by
acouple consisting of the forces in the flanges multiplied by
thedistance between them. Accepting that little error is involved
inassuming that all resistance to bending is offered in this way,
themost efficient system will be one in which the flange forces
arereduced to a minimum to save material, and the distance
betweenincreased accordingly.
Structural principles
Shear forces are resisted by the internal members.This, however,
leaves the problem of accommodating shear forceswhich, in the case
of the I-beam, were absorbed by the web. Tocontinue to provide a
solid web would waste a lot of material. As analternative, discrete
members running diagonally, and sometimesvertically, are used to
carry the shear. The resulting system, giventhe generic name of a
truss, will carry loads over large spans withgreat economy.Trusses
are structurally efficient and particularly popular for longspan
roofs.
Trusses are highly efficient, able to span considerable
distance, andthey are visually light. The economy in use of
materials has led to theuse of truss systems in preference to beams
in a large number ofsituations, both in the vertical and horizontal
planes. They becamepopular solutions to the problem of roofing in
large clear areas suchas factories, workshops and railway stations.
In these situations theincreased structural depth inherent in truss
structures was not undulypunitive. In contrast, their use as floor
support systems washampered by their increased depth.
Long span truss roof
Trusses are typically used for spans of between 10 - 100m, with
aspan:depth ratio of between 10:1 and 15:1.
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Introduction
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