This document provides information on trusses and roof trusses. It defines trusses as rigid structures made of two-force members arranged in triangular frameworks. Common applications include rooftops and bridges. Pitched roof trusses are most common, with a sloped top chord to facilitate drainage. Analysis involves regarding members as pinned joints transferring only axial forces. Common types include Pratt, Howe, Fink, and Mansard trusses, suited to different spans. Roof trusses provide economic construction and easier assembly than conventional roofs.

1. Trusses Introduction
 Trusses are rigid structures made
up of two-force members, which
are objects with exactly two
forces/connections.
 Trusses are commonly found in
the frame of a roof and the sides
of a bridge.
 Trusses are triangular frame
works, consisting of axially
loaded members
 They are more efficient in
resisting external loads as the
cross section of all the members
are nearly uniformly stressed
 They are Extensively used for
Larger Spans

2. Pitched Roof Trusses
Most common types
of roof trusses.
Top chord is provided
with a slope in order to
facilitate natural
drainage of rainwater
and clearance of
dust/snow
accumulation.
The typical span to maximum depth ratios of pitched roof
trusses are in the range of 4 to 8M, the larger ratio being
economical in longer spans.

3. Applications
Trusses are used in
o Roofs of Single Story Industrial Buildings.
o Long Span Floors and Roofs Of Multistory Buildings, to resist gravity
loads.
o Trusses are also used in Walls and Horizontal Planes of Industrial
Buildings to resist Lateral Loads and to provide Lateral Stability.

4. Analysis of Trusses
o Truss members are regarded as being pinned joints.
o They are assumed to be joined together so as to transfer only the axial
forces and not moments and shears from one member to the adjacent
members
o The loads are assumed to be acting only at the nodes of the trusses.
o The trusses may be provided over
• a single span, simply supported over the two end supports, in which
case they are usually statically determinate.
• Such trusses can be analyzed manually by
– method of joints
– method of sections.
• Computer programs are also available for the analysis of trusses.

5. Parts of a Truss
A truss is composed of:
 Joints
 Members
 External forces (reaction forces and applied forces).

6. A two force member is a body that has forces (and only forces, no
moments) acting on it in only two locations. In order to have a two force
member in static equilibrium, the net force at each location must be equal,
opposite, and collinear. This will result in all two force members being in either
tension or compression.

7. Components of Roof Truss

8. Roof Truss Advantages
 Roof trusses can save on-site costs.
 Less labor requirement .
 Faster shell completion time.
 Greater flexibility in locating plumbing, duct work, and electrical wiring
 Floor plan freedom in locating interior partitions often without additional support required
 Fewer pieces to handle and reduced installation time
 Reduced HVAC, plumbing, and electrical subcontractor time on job
 No column pads to pour, no steel beams and posts to place
 Job site material pilferage and cutting waste reduced
Roof Truss Disadvantages
 Roof trusses have a series of supporting members that limit the use of attic space.
 Large trusses require a crane

9. Types of Roof Trusses

10. Types of Roof Truss
o Pitched roof trusses o Parallel chord trusses
o Trapezoidal trusses

11. o The typical span to maximum depth ratios of pitched roof trusses are
in the range of 4 to 8m, the larger ratio being economical in longer
spans.
o These trusses have a greater depth at the mid-span. Due to this even
though the overall bending effect is larger at mid-span, the chord
member and web member stresses are smaller closer to the mid-
span and larger closer to the supports.
o Most common types of roof
trusses
o Top chord is provided with a
slope in order to facilitate
natural drainage of rainwater
and clearance of dust/snow
dust/snow accumulation.
Pitched Roof Trusses

12. Pratt Truss (6-30m)
o In Pratt trusses web members are arranged in such a way that under
gravity load the longer diagonal members are under tension and the
shorter vertical members experience compression.
o This allows for efficient design, since the short members are under
compression.
o However, the wind uplift may cause reversal of stresses in these
members and nullify this benefit.

13. The converse of the Pratt is the Howe truss . This is commonly used in
light roofing so that the longer diagonals experience tension under
reversal of stresses due to wind load.
Howe Truss (6-10m)

14. o Fink trusses are used for longer spans having high pitch roof.
o The web members in such truss are subdivided divided to obtain
shorter members
Fink Trusses(up to 10m)

15. o Fan trusses are used when the rafter members of the roof trusses
have to be subdivided into odd number of panels
Fan Trusses (10-15m)

16. Mansard Trusses(20-30m)
o Mansard trusses are variation of fink trusses, which have shorter
leading diagonals even in very long span trusses, unlike the fink and
fan type trusses.
o The Mansard trusses can be used in the span ranges of 12 m to 30
m.

17. When to use a roof truss:
Roof trusses are characterised by an economic use of construction materials (timber, steel).
Composed of individual lightweight pieces, a truss can also provide considerable advantage in
transport and assembly as compared to conventional roof structures. On the other hand, trusses are
more labour-intensive and require connection devices. However, if a greater number of identical
trusses can be manufactured, then considerable economies of scale can be achieved.The structural
height of a truss is usually larger than the height of similar structures using solid beams. For roofs,
however, this is usually no disadvantage as roofs must often - depending on roof cover material used
- be higher at the ridge and lower at the eaves to facilitate roof drainage and ensure water tightness.
While the use of steel for roof structures almost invariably calls for a truss, it is with timber structures
where the truss has strong competitors. These are the purlin and the rafter roofs.

19. Materials for Roofing

20. Fastenings for Sheeting

21. Side lap Corrugated
Sheet
Flat Cum Corrugated
Sheets