2. Portal frames are made in a variety of shapes and sizes. They
are usually made from steel, but can also be made from
concrete or timber. The portal structure is designed in such a
way that it has no intermediate columns, as a result large
open areas can easily be created within the structure.
Portal Frames are generally used for single storey
construction which require a large unobstructed floor space
ie
Factories
Shopping Centres
Warehouses
3. Internal view of a portal framed
warehouse
From this slide you can see the internal
outline of the portal frame.
At this stage the floor is not in place.
Also note the clear unobstructed floor area
available.
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 intervals.
4. Advantages and disadvantages of steel
Portal Frames
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Advantages
Speed and ease of erection
Building can be quickly closed in and made water tight.
Framework prefabricated in a workshop and not affected by weather.
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.
Disadvantages
Although steel is incombustible it has a poor resistance to fire as it
bends easily when hot.
Subject to corrosion
5. Portal Frame
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. Coated
steel is lowest in cost but limited in life
due to the durability of the finish.
Aluminium develops its own
protective film. Profile sheets are
quick to erect, dismantle and repair.
Galvanised steel purlins span
between the steel rafters.
Wall panels
6. Base joint for Portal Frame
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.
7. Ridge joint for Portal Frame
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 strengthen and increase the bolt
area.
8. Knee joint for Portal Frame
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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.
9. Diagonal bracing for Portal
Frame
With all types of frameworks we must think on stability ie
movement. To help strengthen the framework and prevent
movement diagonal bracing will be used.
10. Cladding rails for Portal Frame
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This slide shows the
cladding rails for
attaching the external
metal cladding panels
to.
These rails can be
fixed horizontal or
vertical depending on
the way the cladding
panels are fixed.
11. Tie cables for Portal Frame
• 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 cladding.
12. External wall detail
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Here we see the finish
of the external
cladding panels with
the lower level facing
brickwork.
The blockwork behind
creates a protective
wall or firewall.
