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G r a c e H e n r y
M i d h u n a S u r e s h
• Developed during second world
war, but now the most
common form of enclosure for
spans of 20 to 60 m.
• Driven by the need to achieve
low-cost building envelope.
• They are usually made from steel,
but can also be made from
concrete or timber.
Portal frames can be defined as two-
dimensional rigid frames that have the
basic characteristics of A rigid joint
between column and beam.
The main objective of this form of design is
to reduce bending moment in the beam,
which allows the frame to act as one
Portal Frames are
generally used for single
storey construction which
require a large unobstructed
floor space i.e.,
They are very efficient for
enclosing large volumes,
therefore they are often used
storage, retail and
commercial applications as
well as for agricultural
TYPES OF PORTAL FRAME
Pitched roof symmetric portal frame
Generally fabricated from UKB sections with a
substantial eaves haunch section, which may be cut
from a rolled section or fabricated from plate. 25 to
35 m are the most efficient spans
Portal frame with internal mezzanine
Floor Office accommodation is often provided
within a portal frame structure using a partial
width mezzanine floor.
Crane portal frame with column brackets
Where a travelling crane of relatively low capacity (up
to say 20 tonnes) is required, brackets can be fixed to
the columns to support the crane rails
Pitched Roof Symmetric
Portal Frame With Internal Mezzanine Floor
Waters Meeting Health Centre, Bolton
Tied portal frame
In a tied portal frame the horizontal movement of
the eaves and the bending moments in the
columns and rafters are reduced.
Mono-pitch portal frame
It is a simple variation of the pitched roof
portal frame, and tends to be used for
smaller buildings (up to 15 m span).
Propped portal frame
Where the span of a portal frame is large and
there is no requirement to provide a clear span,
a propped portal frame can be used to reduce
the rafter size and also the horizontal shear at
Mansard portal frame
A mansard portal frame may be used
where a large clear height at mid-span
is required but the eaves height of the
building has to be minimised.
Curved rafter portal frame
Portal frames may be constructed
using curved rafters, mainly for
Cellular beam portal frame
Rafters may be fabricated from cellular
beams for aesthetic reasons or when
providing long spans.
• The portal structure is designed in such a way that it has no
• A portal frame building comprises a series of transverse
frames braced longitudinally.
• The primary steelwork consists of columns and pitched rafters.
• The light gauge secondary steelwork consists of side rails for walls
and purlins for the roof.
• The roof and wall cladding separate the enclosed space from the
external environment as well as providing thermal and acoustic
FIRST PORTAL FRAME IN
At the EXPOSITION
UNIVERSELLE in Paris 1878,
the engineer HENRI DE DION
progressed the science of
vaulting with the first portal frame
of lattice girders where the forces
were transmitted directly to the
foundations without tie bars. This
Galarie des Machines had a
span of 35m and its pitched roof
shape was a forerunner of many
sheds to follow.
• A high percentage of roofs are
covered with composite profile metal
sheets with a coloured external skin.
• These composite sheets have
approximately 50mm of insulation
sandwiched between two thin metal
sheets or aluminium sheets.
• Galvanised steel purlins span between
the steel rafters.
INTERNAL VIEW OF A PORTAL
• Clear unobstructed floor area is
• With single storey buildings
natural lighting is gained by
placing clear sheets in roof
layout. These sheets will run
from eaves to ridge at suitable
BASE JOINT FOR PORTAL
• The legs or stanchions of the portal
frame need connecting at the bottom
to a foundation.
• Here we can see the base joint
connection in place.
RIDGE JOINT FOR
Shown here is a ridge
joint or apex joint.
It is Important that this
joint is strong hence
the use of wedge
shaped pieces called
gusset pieces to
increase the bolt area.
KNEE JOINT FOR
Again the knee joint must be strong to support the roof
loads and prevent bending.
Gusset pieces will be used to increase strength, give
greater bolt area and prevent deflection under load.
D I A G O N A L
B R A C I N G F O R
P O R TA L F R A M E
With all types
of frameworks we
must think on
movement. To help
diagonal bracing will
CLADDING RAILS FOR
• This slide shows the
cladding rails for attaching
the external metal cladding
• These rails can be fixed
horizontal or vertical
depending on the way the
cladding panels are fixed.
TIE CABLES FOR
• These wire and tubular ties
are used to prevent
sagging of the cladding
rails which can add
considerable force unto the
joints of the external
• Here we see the finish of
the external cladding
panels with the lower level
• The blockwork behind
creates a protective wall or
Speed and ease of erection
Building can be quickly closed in and made water tight.
Framework prefabricated in a workshop and not affected by
Site works such as drainage, roads etc can be carried out until
framework is ready for erection.
No weather hold up during erecting the framework.
Connected together in factories by welding and site connections
should be bolted.
• Cost effectiveness
• Saves time
• Capable taking loads
Although steel is incombustible it has a poor
resistance to fire as it bends easily when hot.
Subject to corrosion
Foundation –in situ
• From left