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Design of Steel Roof Truss- G. S. DeshmukhDesign of Steel
Structures
Design of Steel Roof Truss
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INTRODUCTIONTrusses are triangular frame works in which the
members are subjected to essentially axial forces due to external
load.
External load and the members lie in the same plane.
In case of space trusses members are oriented in three
dimensions and also the loads may act in any direction.*Design of
Steel Roof Truss
Design of Steel Roof Truss
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Lattice GirdersDesign of Steel Roof Truss*lattice girders are
the trusses which frequently used to span long lengths in the place
of solid web girders.
Design of Steel Roof Truss
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Design of Steel Roof Truss*Steel members subjected to axial
forces are generally more efficient than members in flexure since
the cross section is nearly uniformly stressed.Trusses are
extensively used, especially to large span structures.
Design of Steel Roof Truss
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USESDesign of Steel Roof Truss*Trusses are used in Roofs of
single storey industrial buildingsLong span floors and roofs of
multistory buildings, to resist gravity loads [Figs. (a) and
(b)].
Design of Steel Roof Truss
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Design of Steel Roof Truss*Walls of multi-storey buildings and
horizontal planes of industrial buildings to resist lateral loads
and give lateral stability [Figs. (c) and (d)].
long span bridges to carry gravity loads and lateral loads [Fig.
(e)].
Design of Steel Roof Truss
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LOADS ACTING ON TRUSSDesign of Steel Roof Truss*Dead load- 1)
Dead load of claddings 2) Dead load of purlins3) Self weight of the
trusses 4) weight of bracingsLive load As per IS:875-1987
(Reaffirmed 1992).Wind loadEarthquake load As per IS:1893-1985.
Design of Steel Roof Truss
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ANALYSIS OF TRUSSESDesign of Steel Roof Truss*The loads are
assumed to be acting only at the nodes of the trusses.
They are usually statically determinate.
Can be analysed manually by the method of joints or by the
method of sections.
Design of Steel Roof Truss
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CONFIGURATION OF TRUSSESDesign of Steel Roof Truss*Pitched Roof
TrussParallel Chord TrussTrapezoidal Truss
Design of Steel Roof Truss
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TRUSS MEMBERSDesign of Steel Roof Truss*The members of trusses
are made of either rolled steel sections or built-up sections
depending upon the span length, intensity of loading.
Design of Steel Roof Truss
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DESIGN OF TRUSSESDesign of Steel Roof Truss*The design standard
(IS: 800) imposes restrictions on the maximum slenderness ratio,
(l/r), as given below:
Member typeMax l/r limit
Members under compression under loads other than wind/
earthquake load180Tension members undergoing stress reversal due to
loads other than wind loador seismic forces180Members normally
under tension but may have to resist compression underwind
load250Compression flange of a beam against lateral torsional
buckling300Members designed only for tension even though they may
experiencestress reversal350Members always under tension (unless
pre-tensioned to avoid sag)400
Design of Steel Roof Truss
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Design of Steel Roof Truss*These limits are imposed to ensure
the following:Too slender a member is avoided which may be damaged
during transportation and erection.
Members do not sag excessively under self-weight during service
causing excessive deflection in truss.
Compression members do not sag greater than 1/1000th of their
length, which is beyond the imperfection limit assumed in the
compressive strength calculation.
It is a common practice to specify a minimum angle size of 50 X
50 X 6 in the case of roof trusses.
Design of Steel Roof Truss
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Design of Steel Roof Truss*
Design of Steel Roof Truss
