2. . INTRODUCTIONINTRODUCTION PORTAL FRAMEPORTAL FRAME Portal
frames are the most commonly usedPortal frames are the most
commonly used structural forms for singlestructural forms for
single--storeystorey industrial structures. They are
constructedindustrial structures. They are constructed mainly using
hotmainly using hot--rolled sections, supportingrolled sections,
supporting the roofing and side cladding via coldthe roofing and
side cladding via cold--formedformed purlins and sheeting rails.
They may alsopurlins and sheeting rails. They may also be composed
of tapered stanchions and raftersbe composed of tapered stanchions
and rafters fabricated from plate elements. Portal frames
offabricated from plate elements. Portal frames of lattice members
made of angles or tubes arelattice members made of angles or tubes
are also common, especially in the case of longeralso common,
especially in the case of longer spans.spans. Generally, the
centreGenerally, the centre--toto--centre distancecentre distance
between frames is 6 to 7.5m, with eaves heightbetween frames is 6
to 7.5m, with eaves height ranging from 6ranging from 6 --15 m.15
m. Normally, larger spacing of frames is used in theNormally,
larger spacing of frames is used in the case of taller buildings,
from the point ofcase of taller buildings, from the point of
economy.economy. MomentMoment--resisting connections are to be
providedresisting connections are to be provided at the eaves and
crown to resist lateral andat the eaves and crown to resist lateral
and gravity loadings.gravity loadings. 11
4. . INTRODUCTIONINTRODUCTION PORTAL FRAMEPORTAL FRAME 33 The
stanchion bases may behave asThe stanchion bases may behave as
either pinned or fixed, depending uponeither pinned or fixed,
depending upon rotational restraint provided by therotational
restraint provided by the foundation and the connection
detailfoundation and the connection detail between the stanchion
and foundations.between the stanchion and foundations. Portal
frames can be used in timberPortal frames can be used in timber
based commercial and industrialbased commercial and industrial
building construction with clear spans ofbuilding construction with
clear spans of 15 to 30 metres.They provide large15 to 30
metres.They provide large clear spans and good height
clearanceclear spans and good height clearance for use in a range
of applications,for use in a range of applications,
including:including: warehouses and factories,warehouses and
factories, commercial buildings,commercial buildings,
churches,churches, sporting venuessporting venues rural sheds,
etcrural sheds, etc..
5. . INTRODUCTIONINTRODUCTION PORTAL FRAMEPORTAL FRAME Timber
portal frames are cost effective, easilyTimber portal frames are
cost effective, easily accommodate additional lighting, plumbing,
etcaccommodate additional lighting, plumbing, etc and can be
erected quickly. The overalland can be erected quickly. The overall
appearance is also aesthetically pleasing.appearance is also
aesthetically pleasing. Timber portal frames are particularly
suitable forTimber portal frames are particularly suitable for use
in high visual impact applications eguse in high visual impact
applications eg churches, halls, or potentially corrosivechurches,
halls, or potentially corrosive environments eg swimming pool
enclosures,environments eg swimming pool enclosures, buildings
housing chemical manufacturer andbuildings housing chemical
manufacturer and storage, tanneries, etc. Portal frames may
bestorage, tanneries, etc. Portal frames may be made from sawn
timber, Glulam, LVL andmade from sawn timber, Glulam, LVL and
plywood webbed beams. The connections carryplywood webbed beams.
The connections carry significant moments and must have
bothsignificant moments and must have both strength and stiffness
to be effective.Timberstrength and stiffness to be effective.Timber
portal framed buildings may be clad withportal framed buildings may
be clad with conventional metal, or fibre cement cladding,
asconventional metal, or fibre cement cladding, as is common for
warehouses and factories, oris common for warehouses and factories,
or with timber products such as plywood orwith timber products such
as plywood or weatherboards.For other commercialweatherboards.For
other commercial applications, cavity brick, brick veneer,
concreteapplications, cavity brick, brick veneer, concrete
tilttilt--up or concrete blockup or concrete block--work may be
requiredwork may be required for fire isolation or compliance with
local buildingfor fire isolation or compliance with local building
regulations.regulations. 44
6. . INTRODUCTIONINTRODUCTION PORTAL FRAMEPORTAL FRAME Because
of these very strong and rigid jointsBecause of these very strong
and rigid joints some of the bending moment in the rafters issome
of the bending moment in the rafters is transferred to the columns.
This means that thetransferred to the columns. This means that the
size of the rafters can be reduced or the spansize of the rafters
can be reduced or the span can be increased for the same size
rafters.can be increased for the same size rafters. This makes
portal frames a very efficientThis makes portal frames a very
efficient construction technique to use for wide spanconstruction
technique to use for wide span buildings.buildings. Portal frame
construction is therefore typicallyPortal frame construction is
therefore typically seen inseen in warehouseswarehouses,,
barnsbarns and other placesand other places where large, open
spaces are required at lowwhere large, open spaces are required at
low cost and a pitched roof is acceptable. claddingcost and a
pitched roof is acceptable. cladding with cavity masonry work to
the bottom 2m of thewith cavity masonry work to the bottom 2m of
the wall to provide security and impact resistance.wall to provide
security and impact resistance. The lightweight cladding would be
carried onThe lightweight cladding would be carried on sheeting
rails spanning between the columns ofsheeting rails spanning
between the columns of the portal frames.the portal frames. 55
7. . PORTAL FRAMEPORTAL FRAME Portal frames are made in a
variety of shapesPortal frames are made in a variety of shapes and
sizes. There are generally 3 types of portaland sizes. There are
generally 3 types of portal frames :frames :-- Steel portal
frameSteel portal frame Timber portal frameTimber portal frame
Concrete portal frameConcrete portal frame They are usually made
from steel, but canThey are usually made from steel, but can also
be made from concrete or timber. The portalalso be made from
concrete or timber. The portal structure is designed in such a way
that it has nostructure is designed in such a way that it has no
intermediate columns, as a result large openintermediate columns,
as a result large open areas can easily be created within the
structure.areas can easily be created within the structure. Portal
Frames are generally used for singlePortal Frames are generally
used for single storey construction which require a largestorey
construction which require a large unobstructed floor
space.unobstructed floor space. 66 TYPES OF PORTAL FRAMETYPES OF
PORTAL FRAME
8. . STEEL PORTAL FRAMESTEEL PORTAL FRAME PORTAL FRAMEPORTAL
FRAME The early use of the rigid portal frame coincidedThe early
use of the rigid portal frame coincided with the introduction of a
wide range of a coldwith the introduction of a wide range of a cold
formed, profiled steel sheets for roofing, whichformed, profiled
steel sheets for roofing, which could be fixed at a low pitch and
be weathercould be fixed at a low pitch and be weather tight.
Longtight. Long--span portal frames may have a pinspan portal
frames may have a pin-- joint connection at the ridge to allow
somejoint connection at the ridge to allow some flexure between the
rafters of the frame whichflexure between the rafters of the frame
which are pinare pin--jointed to foundation bases to allowjointed
to foundation bases to allow flexure of posts due to spread under
load.flexure of posts due to spread under load. For economy in the
use of a standard section,For economy in the use of a standard
section, short and mediumshort and medium--span steel portal frame
s arespan steel portal frame s are oftn fabricated from one
mildoftn fabricated from one mild--steel Isteel I--section
forsection for both rafters and posts, with the rafters welded
toboth rafters and posts, with the rafters welded to the posts
without any increase in depth at thethe posts without any increase
in depth at the knee.knee. ShortShort--span portal frames may be
fabricated offspan portal frames may be fabricated off site as one
frame. Mediumsite as one frame. Medium--spanspan portal
framesportal frames are generally fabricated in two halves for ease
ofare generally fabricated in two halves for ease of transport and
are assembled on site with boltedtransport and are assembled on
site with bolted connections of the rafters at the ridge, with
highconnections of the rafters at the ridge, with high strength
friction gripstrength friction grip.. 77
9. . STEEL PORTAL FRAMESTEEL PORTAL FRAME PORTAL FRAMEPORTAL
FRAME AdvantagesAdvantages Speed and ease of erectionSpeed and ease
of erection Building can be quickly closed in and madeBuilding can
be quickly closed in and made water tight.water tight. Framework
prefabricated in a workshop and notFramework prefabricated in a
workshop and not affected by weather.affected by weather. Site
works such as drainage, roads etc can beSite works such as
drainage, roads etc can be carried out until framework is ready for
erection.carried out until framework is ready for erection. No
weather hold up during erecting theNo weather hold up during
erecting the framework.framework. Connected together in factories
by welding andConnected together in factories by welding and site
connections should be bolted.site connections should be bolted.
DisadvantagesDisadvantages Although steel is incombustible it has a
poorAlthough steel is incombustible it has a poor resistance to
fire as it bends easily when hot.resistance to fire as it bends
easily when hot. Subject to corrosionSubject to corrosion 88
10. . PREPRE--CAST REINFORCED CONCRETE FRAMECAST REINFORCED
CONCRETE FRAME PORTAL FRAMEPORTAL FRAME For several years following
the end ofFor several years following the end of the second world
war(1945) there was athe second world war(1945) there was a
considerable shortage of structural steelconsiderable shortage of
structural steel in this country and it was then that thein this
country and it was then that the reinforced concrete portal frames
camereinforced concrete portal frames came into common use for
agricultural,into common use for agricultural, storage, factory,
and other singlestorage, factory, and other single-- storeyed
buildings.storeyed buildings. a limited range of standard, prea
limited range of standard, pre--castcast reinforced concrete portal
frames wasreinforced concrete portal frames was supplied for the
economic benefit ofsupplied for the economic benefit of repitetive
casting in standard mouldsrepitetive casting in standard moulds and
close control of mixing, placing andand close control of mixing,
placing and compaction of concrete that is possiblecompaction of
concrete that is possible in factory conditions.in factory
conditions. 99
11. . TYPES OF CONCRETE PORTAL FRAMETYPES OF CONCRETE PORTAL
FRAME PORTAL FRAMEPORTAL FRAME Symmetrical pitch
reinforcedSymmetrical pitch reinforced concrete portal frame
constructionconcrete portal frame construction This the most
structurally efficient and mostThis the most structurally efficient
and most commonly used type of concrete portal frame.commonly used
type of concrete portal frame. it has been used for factories,
warehouses,it has been used for factories, warehouses, barns, sheds
and singlebarns, sheds and single--storey places ofstorey places of
assembly.the slope of the rafters and spacing ofassembly.the slope
of the rafters and spacing of purlins and sheeting rails is usually
arranged topurlins and sheeting rails is usually arranged to suit
fibre cement or profiled steel sheeting.suit fibre cement or
profiled steel sheeting. North light preNorth light pre--cast
reinforcedcast reinforced concrete portal frame
constructionconcrete portal frame construction The most economical
span for this profile ofThe most economical span for this profile
of frame is up to about 9.0 to minimise the volumeframe is up to
about 9.0 to minimise the volume of roof space inside the frames
and to avoid theof roof space inside the frames and to avoid the
large sections of frame that would be necessarylarge sections of
frame that would be necessary with greater spans. The southwith
greater spans. The south--facing slope isfacing slope is pitched at
22 degrees and the northpitched at 22 degrees and the north--facing
slopefacing slope at 60 degrees to the horizontal.at 60 degrees to
the horizontal. 1010
12. . PREPRE--CASTREINFORCED CONCRETE FRAMECASTREINFORCED
CONCRETE FRAME PORTAL FRAMEPORTAL FRAME AdvantagesAdvantages There
was a ready supply of a limited range ofThere was a ready supply of
a limited range of standard frames that could rapidly bestandard
frames that could rapidly be transported, erected, and finished at
antransported, erected, and finished at an economic cost.economic
cost. they require no maintainance during the usefulthey require no
maintainance during the useful life of the building.life of the
building. it has a better resistance to collapse duringit has a
better resistance to collapse during fires than an unprotected
steel frames.fires than an unprotected steel frames. economy of
section area gained by the use ofeconomy of section area gained by
the use of the plastic method of design in the design ofthe plastic
method of design in the design of steel frames is considerably less
with reinforcedsteel frames is considerably less with reinforced
concrete.concrete. cover of concrete to the steel reinforcement
tocover of concrete to the steel reinforcement to inhibit rust and
give protection during fires.inhibit rust and give protection
during fires. DisadvantagesDisadvantages they have to be formed in
standard sizethey have to be formed in standard size moulds, for
the sake of economy, there is only amoulds, for the sake of
economy, there is only a limited range of sizes.limited range of
sizes. 1111
13. . TIMBER PORTAL FRAMETIMBER PORTAL FRAME PORTAL FRAMEPORTAL
FRAME Combinations of slender timber sectionsCombinations of
slender timber sections glued, or glued or nailed together,
areglued, or glued or nailed together, are used in portal frames
for mediumused in portal frames for medium--andand longlong--span
roofs for such buildings asspan roofs for such buildings as
churches, assembly halls, sports hallschurches, assembly halls,
sports halls and other singleand other single--storey structures
wherestorey structures where the timber portal frames are exposed
forthe timber portal frames are exposed for appearance
sake.appearance sake. 1212
14. . TYPES OF TIMBER PORTAL FRAMETYPES OF TIMBER PORTAL FRAME
PORTAL FRAMEPORTAL FRAME SymmetricalSymmetrical--pitch glued
laminatedpitch glued laminated timber portaltimber portal These
portal frames are usually fabricated in twoThese portal frames are
usually fabricated in two sections for ease of transport and are
boltedsections for ease of transport and are bolted together at the
ridges. These comparativelytogether at the ridges. These
comparatively expensive portal frames are spaced fairly
widelyexpensive portal frames are spaced fairly widely apart to
support timber or steel purlins which canapart to support timber or
steel purlins which can be covered with any of the sheet
materials,be covered with any of the sheet materials, slates or
tiles.slates or tiles. Flat gluedFlat glued--andand--nailed timber
portalnailed timber portal The flat portal frame is designed for
the mostThe flat portal frame is designed for the most economic use
of timber glued together with theeconomic use of timber glued
together with the top and bottom booms of glued laminate withtop
and bottom booms of glued laminate with web stiffners. The portal
frames are widelyweb stiffners. The portal frames are widely spaced
to support metal decking on the roof andspaced to support metal
decking on the roof and profiled sheeting on the walls.profiled
sheeting on the walls. 1313
15. . TIMBER PORATL FRAMETIMBER PORATL FRAME PORTAL FRAMEPORTAL
FRAME AdvantagesAdvantages Timber has a natural resistance to
fungalTimber has a natural resistance to fungal decay.decay. insect
attack can be prevented by impregnatinginsect attack can be
prevented by impregnating timber with insecticide
preservative.timber with insecticide preservative. timber, which is
a combustible material, is nottimber, which is a combustible
material, is not easy to ignite in the sizes usual to
buildings.easy to ignite in the sizes usual to buildings. Once
ignited, timber burns very slowly andOnce ignited, timber burns
very slowly and forms a protective layer of charcoal on itsforms a
protective layer of charcoal on its surface which insulates the
remainder from thesurface which insulates the remainder from the
worst effects of fire.worst effects of fire. the surface of soft
wood timber can be treatedthe surface of soft wood timber can be
treated with flame retardants to achieve necessary ratewith flame
retardants to achieve necessary rate of flame spread.of flame
spread. 1414
16. INTERNAL OUTLINE OF THE PORTAL FRAMEINTERNAL OUTLINE OF THE
PORTAL FRAME PORTAL FRAMEPORTAL FRAME 1515 clear unobstructed
floorclear unobstructed floor area available.area available. With
single storey buildingsWith single storey buildings natural
lighting is gained bynatural lighting is gained by placing clear
sheets in roofplacing clear sheets in roof layout.layout. These
sheets will run fromThese sheets will run from eaves to ridge at
suitableeaves to ridge at suitable intervals.intervals.
17. SHEETINGSHEETING PORTAL FRAMEPORTAL FRAME 1616 A high
percentage of roofsA high percentage of roofs are covered with
compositeare covered with composite profile metal sheets with
aprofile metal sheets with a coloured external skin.coloured
external skin. These composite sheetsThese composite sheets have
approximately 50mmhave approximately 50mm of insulation
sandwichedof insulation sandwiched between two thin metalbetween
two thin metal sheets or aluminium sheets.sheets or aluminium
sheets. Coated steel is lowest inCoated steel is lowest in cost but
limited in life due tocost but limited in life due to the
durability of the finish.the durability of the finish. Aluminium
develops its ownAluminium develops its own protective film. Profile
sheetsprotective film. Profile sheets are quick to erect,
dismantleare quick to erect, dismantle and repair.and repair. Wall
panelsWall panels
18. BASE JOINTBASE JOINT PORTAL FRAMEPORTAL FRAME 1717 Legs of
portal frameLegs of portal frame connected with theconnected with
the base of foundation.base of foundation.
19. RIDGE JOINTRIDGE JOINT PORTAL FRAMEPORTAL FRAME 1818 ridge
joint or apex joint. wedge shaped pieces called gusset pieces to
strengthen and increase the bolt area.
20. KNEE JOINTKNEE JOINT PORTAL FRAMEPORTAL FRAME 1919 knee
joint must be strong toknee joint must be strong to support the
roof loads andsupport the roof loads and prevent bending.prevent
bending.