2. TRUSS
Trusses are triangular frame works in which the members are subjected to essentially axial forces
due to externally applied load.
Trusses are frequently used to span long lengths in the place of solid web girders and such
trusses are also referred to as lattice girders.
Steel members subjected to axial forces are generally more efficient than members in flexure
since the cross section is nearly uniformly stressed.
Trusses are used in roofs of single storey industrial buildings, long span floors and roofs of
multistory buildings, to resist gravity loads . Trusses are also used in multi-storey buildings and
walls and horizontal planes of industrial buildings to resist lateral loads and give lateral stability .
Trusses are used in long span bridges to carry gravity loads and lateral loads.
3. TERMS USED IN THE ROOF TRUSSES
TOP CHORD - The uppermost line of members that extend from one
support to the other through the apex is called top chord. The top
chord is also known as the upper chord of the roof truss.
BOTTOM CHORD - The lowermost line of members of truss extending
from one support to the other is called bottom chord. The bottom
chord is also known as lower chord of the root truss.
SPAN - The distance between the supporting end joints of a truss is
called its span. When supported on walls, the distance between the
centre of bearings would be considered as span. When framed into
columns the distance between the column faces may be regarded as
the span.
RISE - The rise of a roof truss is the vertical distance measured from the
apex to the line joining supports.
PITCH - The ratio of the rise to the span is called the pitch of a roof
truss. A pitch of 114 is most common and economical. The pitches 113
and 115 and corresponding to an angle of inclination of 30' are also
commonly employed.
Other terms – Panel, Rafter, Eaves, Purlins, Ridge, Sag tie, Slope, Bay, Sub
purlin, Sheathing , Spacing of purlins etc.
5. PRATT TRUSS
PRATT TRUSS
• Span range – 20 to 100 m
• Use – it can be used in bridges, railways , and where as long span needed.
• The material in the frame structure is structural steel.
• The main beams along the bridge have square box profiles with height 200
mm and thickness 16 mm. This also includes the outermost diagonal
members.
• The diagonal and vertical members have a rectangular box section 200x100
mm, with 12.5 mm thickness. The large dimension is in the transverse
direction of the bridge.
• • The transverse horizontal members at the top of the truss (struts) are
made from solid rectangular sections with dimension 100x25 mm.
• The transverse horizontal members supporting the roadway (floor beams)
are standard HEA100 profiles.
HEA
Height
H
Width
W
Thickness
tw
100 96 100 5
6. WARREN TRUSS
PRATT TRUSS
• Span range – 20 to 100 m
• This type of truss is also used for the horizontal truss of gantry/crane
girders.
• In this type of truss, diagonal members are alternatively in tension and in
compression.
• The material in the frame structure is structural steel.
• The Warren truss has equal length compression and tension web member.
• Warren truss contains a series of isosceles triangles or equilateral triangles.
To increase the span length of the truss bridge, verticals are added for
Warren Truss. Pratt truss is characterized by having its diagonal members
(except the end diagonals) slanted down towards the middle of the bridge
span.
7. FINK TRUSS
FINK TRUSS
• Span range – 10 to 15 m
• TRUSS HAVE HEIGHT 3M.
• This type of truss is more commonly used for the roof of houses.
• The material in the frame structure is structural steel.
• Blue – compression
• Red – tension
8. NORTH LIGHT TRUSS
FINK TRUSS
• Span range – 10 to 15 m
• TRUSS HAVE HEIGHT 3M.
• North light trusses are traditionally used for short spans in industrial
workshop-type buildings. They allow maximum benefit to be gained from
natural lighting .
• The material in the frame structure is structural steel.
• Blue – compression
• Red – tension
