Industrial construction consist of the buildings including terrace factories or
workshops, detached factories, warehouse, factory canteens, markets, hawker
centers, sports halls, industrial training centers, etc.
These are characterized by large clear open spaces under light roof structures.
Steel has been used for framing skyscrapers and other commercial buildings for a
long time. The main reason for selection of steel is; the restrictive fire codes and
the requirement for long, clear spans.
Timber is being highly substituted by steel due to higher quality, easy availability
and competitive price of steel framing members compared to timber.
STRUCTURAL STEEL ARE DIVIDED INTO TWO MAIN
GROUPS ACCORDING TO THE MANUFACTURE
1) Hot rolled sections
2) Those obtained by cold rolling.
The former comprise of the heavier sections.
Steel components are used in 5 ways:
1) As beams and lintels for members which suffer bending stresses.
2) As columns which resist compression and bending stresses.
3) As ties where the stresses are tensile
4) In roof trusses and lattice girders where the forces are compressive and tensile, and
5) For reinforcement in reinforced concrete.
Steel framework consists of beams, channels, angles, etc. The fastenings between the
different parts of a frame is by means of bolts, rivets and welding used in 4 ways.
TRUSS FRAMES OR LATTICE GIRDERS are usually more economical in terms
of material required.
PORTAL FRAMES are cheaper to fabricate faster in construction and have
advantages in aesthetic, ease of maintenance and added headroom, unobstructed by
ties or bracing members.
STEEL PORTAL FRAMES
A portal frame is distinguished by the rigid connection of the rafters to the posts of the
frame so that under load moments are distributed through the rafter and the post. It consist
of (i) Grade 350 steel I-section columns and rafters, and (ii) the column foundations.
Short and medium span frames the apex or ridge, where the rafters connect, is generally
made as an on-site, rigid bolted connection for convenience in transporting half portal
Short-span portal frames may be fabricated off site as one frame. Medium-span portal
frames are generally fabricated in two halves for ease of transport and are assembled on
site with bolted connections of the rafters at the ridge, with high strength friction grip
Rafters & posts from same
Section of steel beam
Short-span portal frame
LONG SPAN STEEL PORTAL FRAMES
• They have the connection of the rafters to the posts at the knee, hunched to make the
connection deeper than the main rafter section for additional stiffness.
•In long span steel portal frames the posts and lowest length of the rafters, towards the
knee, may often be fabricated from cut and welded I-sections so that the post section and
part of the rafter is wider at the knee than at the base and ridge of the rafter.
•Portal frames with a span of up to 15m are defined as short span, frames with a span of
16m to 35m as medium span and frames with a span of 36m to 60m as long span.
COMPONENTS OF A PORTAL FRAME
1.Portal column consisting of two "C" section purlins bolted together
2.The joints have a 10mm MS steel plate sandwiched between the "C" sections
3.Portal rafter consisting of two "C" section purlins bolted together
4.Fly brace, flat galv. strap bolted to rafter and roof purlins. Stiffens the rafter
5.Knee brace consisting of two "C" section purlins bolted together
6."Z" section purlin bolted direct (no cleat)through the bottom flange to the portal rafter
7."C" section girt bolted direct (no cleat)through the flange to the portal column
The haunched connection of the rafters to the posts can be fabricated either by welding a
cut I-section to the underside of the rafter, as illustrated in given Fig, or by cutting and
bending the bottom flange of the rafter and welding in a steel gusset plate.
The junction of the rafters at the ridge is often stiffened by welding cut I-section to the
underside of the rafters at the bolted site connection
Steel portal frames may be fixed to or pinned to bases to foundations. For short span portal
frames, where there is comparatively little spread at the knee or haunch, a fixed base is often
used. It will be seen from that the steel base plate, which is welded through gusset plates to the
post of the portal frame, is set level on a bed of cement grout on the concrete pad foundation
and is secured by four holding-down bolts set or cast into the concrete foundation.
The frames are designed for the following loads:-
dead load wind load
THE IMPORTANCE OF PROPERLY DESIGNED JOINTS
If the joints at B, C and D are not rigid, they will “open up”, and the frame will be unstable
when subjected to loads (“pack of cards effect”)
Buckling of Rafters
The rafter of the portal frame is a slender structural element, and unless it is restrained it will
buckle when loaded.
In a braced roof this restraint is provided by the purlins acting together with a braced bay. The
purlins provide the restraining force for the rafters, and the braced bay acts as a “buttress”
which absorbs these purlin restraining forces.
While this system is effective in restraining the top flange of the rafter I-beam, the bottom
flange remains relatively unrestrained, and to achieve the requisite restraint, short lengths of
angle iron are connected at intervals between the bottom flange of the I-beam and the purlins
as shown. This simple and necessary anti-buckling feature is sometimes neglected in the design
of portal frames.
A building subjected to wind forces along its length will tend to collapse as shown a above,
while a building with a braced side bay as shown below will be stable, since the braced bay will
function as a “buttres” to resist the wind forces, and transfer them to the foundations.
The spacing of the purlins and sheeting rails depends on the type of roof and wall sheeting
used. The deeper the profile of sheeting the greater its safe span and the further apart the
purlins and sheeting rails may be fixed .
The section of purlins and sheeting rails depends on the most economic spacing of the
structural frames .
The greater the spacing of frames the greater will be the dead weight of sheeting and
imposed loads, and the deeper the section of purlin and rail necessary to support the weight
of the roof and wall covering.
Before 1960 most purlins and sheeting rails were of standard mild steel sections , angle
sections being common for closely spaced frames and channel sections for more widely
spaced frames .
Angle and channel sections :
Angle and channel sections were suited to the hook bolt fixings then used for corrugated
asbestos cement and steel sheeting .
Angle and channel section purlins and sheeting rails are fixed to short length of steel angle
cleat bolted to the top flange of rafters and to columns .
Portal frame GABLE END FRAMING
Portal frame base
Gable post fixed to pad
foundation and underside of portal
Steel angle joint purlin
cleat bolted to rafter of
CONNECTION TO PURLIN TO
Holes for fixing next length
PURLIN BRACES ANTI SAG BARS TO
WIND BRACING TO
STEEL TRUSS ROOF ON
Mild steel angle
STEEL SECTION PURLIN AND
WASHER PLATES AND
SHEETING RAILS TO SUPPORT
SHEET METAL AND ASBESTOS
A lattice girder is a girder where the flanges are
connected by a lattice web. This type of design has been
supplanted in modern construction
with welded or bolted plate girders, which use more
material but have lower fabrication costs. The lattice
girder was used prior to the development of larger
rolled steel plates.
The lattice girder, like any girder, primarily
THE ADVANTAGE OF THIS
SINGLE BAY FRAME :-
It is the economy in the use of materials
by the use of small section angle, tubular
or flat standard mild
steel sections for the trusses that can be
economically fabricated and quickly
THE DISADVANTAGES ARE
• very considerable volume of roof space
inside the triangular roof frames cannot be
used for any purpose other than housing
services such as lighting and heating,
•Where the activity enclosed by the
building requires heating, the roof space
has to be wastefully heated as well as the
useful space below.
SINGLE BAY SYMMETERICAL PITCH LATTICE STEEL ROOF
TWO BAY SYMMETERICAL PITCH LATTICE STEEL ROOF
A disadvantage of the multi-bay valley
beam form of construction is that there
is very limited depth alongside the valley
beam for the fall (slope) of rainwater
pipes from valley gutter outlets to
rainwater down pipes fixed to internal
columns. The shallow fall rain water
pipes that are run alongside valley
beams will require sealed joints and the
shallow fall pipe will more readily
become blocked than a straight down
pipe from valley outlets.
TWO BAY SYMMETERICAL PITCH LATTICE STEEL ROOF
The lattice girder supports
half of each truss with each
half cantilevered each side
of the truss, hence the name
'cantilever truss' roof. The
outline in section of the
column and the truss
each side of the lattice
girder resembles an
umbrella, hence the name
SYMMETRICAL PITCH LATTICE STEEL CANTILEVER
With increase in the span of a
triangular roof truss
the volume of unused roof
space and the roof framing
increases and it is, therefore, of
advantage to combine
several bays of the shed frame
construction to provide
cover with the least volume of
roof space and roof
To minimize the number of internal columns that would otherwise obstruct the
floor, the 'umbrella’ or cantilever roof was adopted. Lattice girders constructed
at mid span in each bay support the trusses and widely spaced internal columns
in turn support the lattice girders to provide maximum unobstructed floor space.
NORTH LIGHT TRUSS
To avoid sun glare and overheating in summer the
north light roof profile was introduced, a light
section steel roof truss asymmetrical in profile
with the steeply sloping roof fully glazed and
North light steel lattice truss construction
Roof lights in the slopes of symmetrical pitch
DISADVANTAGE roofs, which are generally set in east and west
facing slopes, may cause discomfort through
overheating in summer and disrupt
manufacturing activities by the glare from
sunlight. To avoid these possibilities the north
light roof is used. The north light roof has an
asymmetrical profile with the south facing
slope at 17° or more to horizontal and the
north facing slope at from 60° to vertical.
NORTH LIGHT TRUSS
Joinery details of