Steel Roof Trusses 2

-Asst Prof.
Farha Shermin
-Asst Prof. Prabhat K Rao
-Asst Prof. Shruti Mutalikdesai
-Asst Prof. Kuladeep Kumar
STEEL ROOF TRUSSES

Lecture 2
Building Construction IV
What are Steel roof trusses?
A truss is essentially a triangulated system

of straight interconnected structural
elements
Steel roof trusses are trusses commonly
fabricated from angle sections and plates.
Channel sections and T-Sections can also
be used.
The main reasons for using trusses are:
Long span
Lightweight
Controlled deflection
Opportunity to support considerable

loads.
Advantages
Sections are readily available in the required dimension, ensures minimum

wastage of material.
Light in weight and can be fabricated in any shape.
Stronger and more rigid in comparison to timber. The members are equally
strong in tension as well as compression.
Types of trusses
PITCHED ROOF TRUSSES

-Most common types of roof trusses are pitched roof trusses wherein the top chord is
provided with a slope in order to facilitate natural drainage of rainwater and clearance
of dust/snow accumulation.
-These trusses have a greater depth at the mid-span.
PARELLEL ROOF TRUSSES

-The parallel chord trusses are used to support North Light roof trusses in industrial
buildings as well as in intermediate span bridges. Parallel chord trusses are also used as
pre-fabricated floor joists, beams and girders in multi-storey buildings.
-The advantage of parallel chord trusses is that they use webs of the same lengths and
thus reduce fabrication costs for very long spans.
TRAPEZOIDAL TRUSSES
-In case of very long span length pitched roof, trusses having trapezoidal configuration,
with depth at the ends are used.
Types of trusses
PITCHED ROOF TRUSSES
PARELLEL ROOF TRUSSES
TRAPEZOIDAL TRUSSES
Various types of Pitched Roof Trusses
Kingpost Truss
Queen post Truss
North Light Truss
Butterfly Truss
Bow-string Truss
Portal Frames
Space frames
King post Truss
The king post truss is used for
simple roof trusses and short-span
bridges.
It is the simplest form of truss in
that it is constructed of the fewest
number of truss members
(individual lengths of wood or
metal).
The truss consists of two diagonal
members that meet at the apex of
the truss, one horizontal beam that
serves to tie the bottom end of
the diagonals together, and the
king post which connects the apex
to the horizontal beam below.
King post Truss
Queen post Truss
Northlight Truss
When the floor span exceeds 15m, it is generally more economical to change
from a simple truss arrangement to one employing wide span lattice girders
which support trusses at right angles.
In order to light up the space satisfactorily, roof lighting has to replace or
supplement, side lighting provision must also be made for ventilation from the
roof.
One of the oldest and economical methods of covering large areas is the
North Light.
This roof consists of a series of trusses fixed to girders. The short vertical side
of the truss is glazed so that when the roof is used in the Northern Hemisphere,
the glazed portion faces North for the best light.
It can be used for spans from 20-30m.
Used for industrial buildings, drawing rooms etc.
Northlight Truss
Butterfly Truss
Bow-String Truss
Portal frames
A continuous rigid frame with a restrained joint between the column and
beam.
A portal frame consists of vertical member called Columns and top member
which may be horizontal, curved or pitched.
Rigidly connected
They are used in the construction of large sheds, bridges and viaducts.
The base of portal frame may be hinged or fixed.
The portal frames have high stability against lateral forces
A portal frame is a statically indeterminate structure.
In the case of buildings, the portal frames are generally spaced at intervals of
3 to 4m
Portal frames are simple in construction, where limited number of trades and skills
are required to construct.
It has a very large spanning comabititly where it can span 15-45m column free.
It can constructed quickly and easily through its basic shape.
Portal frames
Types of Portal Frames
There are three types of portal frames these are rigid bases and
2 Pin and 3 Pin portals.
Rigid Bases
There are lower bending momnets in frame which means the
frame can be lighter and have a heavier footing.
The maxium bending moment is at the apex knee and base of the
frame.
Pinned Based (2 Pinned & 3 Pinned)

These are ralely used anymore as the rigid bases are the
perfered option.
It has a simplified footing where the bending moments are
transmitted vertically to the ground.
This option is more suittable for poor foundations then ridged
bases.
Portal frames
Portal frames
Space frames
Space frames
A spaceframe is a long spanning three

dimensional spatial structure based on the rigidity
of triangle and composed of linear elements
subject only to axial tension and compression
Simplest spatial unit Tetahedran

Four Joints and six structural members
Space frames
Space frames
Space frames
Space frames
Space frames
Space frames
Roofing
Aluminium Roofing
Asbestos Cement Roofing
GI sheet Roofing
Aluminium Roofing Sheet
Aluminium roofing sheets are extremely light and have a high strength-to-
weight ratio.
Corrosion : It is corrosion-resistant in almost any kind of environment. Even in
highly corrosive industrial environments, it is resistant to fumes and vapours
of organic compounds and to chemicals like ammonia, carbon dioxide and
acids such as hydrochloric acid, nitric acid and sulphuric acid. Such corrosion
resistance gives the metal a long life and keeps it looking good throughout
its life.
Aesthetics : The shine and brightness of aluminium livens its surroundings, and,
because it doesn't stain, discolour or rot, it keeps its brightness and shine for
a long time. Aluminium corrugated sheets can take a variety of finishes,
colours and textures, which protect them and further enhance their
appearance.
Transportation : Can be easily dismantled, transported and re-assembled in
a new location.
Though the metal is a good conductor of heat, its high reflectivity for radiant
heat and light (75 to 80 per cent when new, 60 per cent after several
years) keeps the interiors of aluminium building from five to eight degrees
Celsius cooler in summer, while its low emission rate cuts heat loss in winter.
Maintenance : It is easy to maintain and wash.
Circular Corrugated Roofing Sheet 0.30
1.22 mm
Easy to install and dismantle, these sheets are light in
weight. The corrugated pattern on these sheets make these
even more applicable for different roofing purposes in
industrial as well as residential sectors.
Industrial troughed sheets 0.40 1.63mm

Manufactured using high grade aluminium, these sheets are
characterized by applaud able features like durability, high
strength and corrosion resistance. The advanced machines
used by us for the fabrication of this range ensure sooth
surface and fine finish of these roofing sheets.
Pre Painted Aluminium Roofing Sheet

Designed with corrugated patterns, these sheets are made
using pre-painted aluminium. Such value-added attributes
of these sheets have increased their demand in markets.
Asbestos Cement Roofing
AC sheets are mabe of

Asbestos, Fibre(15%) and
Portland Cement.
They are used in Industrial
Buildings, Cinemas, Sheds
and residential areas
because they are cheap,
durable, fire resistant and
vermin resistant.
Construction with AC sheets
is faster compared to the
tiling.
Laying of sheets
GI Sheet Roofing
G.I Sheet are basically stronger than AC sheet.
The corrugations impart additional strength to the GI sheet.
Made with Iron sheets which are galvanised with zinc to protect them them from rusting
action of water and wet weather.
These sheets are fixed in a manner similar to the AC sheets.
End lap should not be less than 15 cm and side lap varies from 1.5 to 2 corrugations.
The holes are either drilled or punched in the sheet crowns.
The sheets are secured to purlins by means of GI hook bolts, screws and nails etc. with
curved washers.
GI Sheet Roofing
Galvanization (or galvanisation) is the process of applying a protective zinc coating to steel or iron, in
order to prevent rusting.
1. Lowest first cost. Galvanizing is lower in first cost than many other commonly specified protective
coatings for steel.
2. Less maintenance/Lowest long term cost. Even in cases where the initial cost of galvanizing is higher
than alternative coatings, galvanizing is almost invariably cheapest in the long term (because it lasts
longer and needs less maintenance).
3. Long life. The life expectancy of galvanized coatings on typical structural members is far in excess of
50 years in most rural environments, and 20 to 25 years plus, even in severe urban and coastal
exposure.
4. Toughest coating. A galvanized coating has a unique metallurgical structure which gives outstanding
resistance to mechanical damage in transport, erection and service.
5. Ease of inspection. Galvanized coatings are assessed readily by eye, and simple non-destructive
thickness testing methods can be used. The galvanizing process is such that if coatings appear sound
and continuous, they are sound and continuous.
6. Faster erection time. As galvanized Iron sheet members are received they are ready for use. No time
is lost on-site in surface preparation, painting and inspection. When assembly of the structure is
complete, it is immediately ready for use, or for the next construction stage.
7. A full protective coating can be applied in minutes; The galvanizing process is not dependent on
weather conditions.

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-Asst Prof.

STEEL ROOF TRUSSES

A truss is essentially a triangulated system

Opportunity to support considerable

Sections are readily available in the required dimension, ensures minimum

PITCHED ROOF TRUSSES

PARELLEL ROOF TRUSSES

PITCHED ROOF TRUSSES

PARELLEL ROOF TRUSSES

Pinned Based (2 Pinned & 3 Pinned)

A spaceframe is a long spanning three

Simplest spatial unit Tetahedran

Industrial troughed sheets 0.40 1.63mm

Pre Painted Aluminium Roofing Sheet

AC sheets are mabe of

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