1. UNIT 16 FORMWORK AND SCAFFOLDING
Structure
16.1 Introduction
Objectives
16.2 Formwork
16.2.1 Requirements of Good Formwork
16.2.2 Economy in Formwork
16.2.3 Materials
16.3 Typesof Formwork
16.3.1 Timber Formwork
16.3.2 Steel Formwork
16.3.3 Climbing Formwork
16.3.4 Moving Formwork
16.3.5 PermeablePormwork
16.3.6 Permanent Prestressed Concrete Formwork
16.4 Removal and Maintenanceof Formwork
16.5 Scaffolding
16.5.1 Types of Scaffolding
16.5.2 Double Scaffolding
16.5.3 Steel Scaffolding andCentering
16.5.4 U-Frame Scaffolding
16.6 Summary
16.7 Key Words
16.8 Answers to SAQs
16.1 INTRODUCTION
In previous unit you studied aboutPiles and Caissonsand their constructionmethods etc.
In this unit, you will studyFormwork and Scaffolding.
The term ''Formwork indicatesa temporary structureerected toreceive wet concreteand
to hold it in place, till it is sufficientlyhard and strong to be self-supportingwithout any
deformation. The other synonymousterms used are: shutteringandcentering. The
1 formworkcanbe of different materials and different types depending upon the type of
I structureandsiterequirements, economy,safetyand qualityrequired in the ftnishedwork.
The "Scaffolding" is a temporary structure which isused in building constructionto
supportplatformsforworkers,structural materialsand constructionequipmentrequired
I
during constructionat elevatedheights. The scaffoldingis useful in building construction,
maintenance,demolitionand repair works.
Objectives
At the end of this unit, you shouldbe able to :
i
* distinguishbetween 'Formwork' and Scaffoldmg,
i * describedifferentmaterialsused informwork and scaffolding,
1 * describeessentialrequirementsof formworkand scaffolding,and
* understand functioningof different types of formwork and scaffolding.
16.2 FORMWORK
'Ibe economicaldesign and constructionof formwork is of great importanceas the cost of
formworkis a large proportion of the total cost of the structureand is most difficult part to
estimate. The appearanceof finished structure and the speed with which the work can be
executedalsodepend mainly on the efficient constructionof formwork.
2. Chstmctirn~efludq~~ea Jthough the formwork is a temporary structure,which shouldbe readily dismantableand
lovable, it is designedto withstand the likelypressures and loads coming on the member
during concreting.Poor formwork design and performanceleavesbehind permanent scars
on the structure and has led to failuresin concreteconstruction. Some of the common
deficienciesnoticed are lack of allowance in designfor loadingslike wind,equipment,
temporary material storage,inadequateanchorageagainstuplift, insufficientslenderness
ratioof compressionmembers, impact of constructionequipmentand leakingjoints etc.
Let us now first examine the requirements for a good formwork.
16.2.1 Requirements of Good Formwork
a) It should be carefully designed,so as tobe strong enough to resist the pressure
of freshconcrete and the super-imposed loads due to men, materials and
equipmentetc.
b) It shouldbe rigid enough to retain its original shapewithoutundue deformation
which isnonnally restricted to 1/300th of spaninnormalcases.
c) It should be tight enoughso as not to allow cement and other materials to leak
through thejoints.
d) The formwork shouldnot warp, bulge, bend or sink and should remaintrue to
.the designedsize.
e) The inner surfaceof the formwork shouldbe smooth so as to givepleasing
appearance to the finishedsurface.The inner surfaceis also applied with
mould oil to facilitate its removal.
16.2.2 Economy in Formwork
A formwork systemis economical only when it fulfils all the tasks on hand with a few
versatilecomponents.You are aware that total cost of concrete construction includesthe
cost of the formwork. However, sometimes the cost of formwork,which actually does not
formpart of the finishedconcretestructure,may exceedthe cost of concrete itself.
Therefore, we should make all'efforts to rninimise the cost of formwork while keeping the
safety aspects in view. Formwork costmainly constitutesthe cost of materials and labour
required for fabrication,erectionand removal of forms.These costs can be minimised by
keeping some good points in mind which will lead to economy in formwork.These good
points, steps or measures are now givenbelow :
a) Avoid use of irregular shapes of forms.
b) The formwork should be fabricatedinto modular sizes and in sufficient
numbers so as to allow re-use.
c) - The structurecomponentsof the building shouldbe so dimensioned and
designed,so as to permituse of commerciallyavailableforms in the market.
d) The working drawings of the formwork shouldbe properly prepared and
checkedbefore fabricating the same.
e) The various components of the formworkshouldbe prefabricated on the
ground,using power equipment. This will reduce labour costs and delays and
holdups in the work. Also, the labour can work more efficientlyon the ground
than on the scaffoldingat an elevated level.
f) The formwork design shouldbe balanced design so as to provide adequateand
not excessivestrengthand rigidity.
g) Where possible, adopt assembly line methods in fabricatingformwork to
increasethe efficiencyof the labourers.
h) In timber formwork,where possible, use doubleheaded nails to facilitate their
removal.
i) Constructionjoints shouldbejudiciously incorporatedto reduce the quantityof
forms required in one operationthus enabling re-use.
j) When mechanical vibrators are used, bolts mustbe employed insteadof wire
ties or nails to ensure safety.
k) The formwork shouldbe handled and stackedcarefully.It shouldbe oiled and
cleaned after each use to prolong its usage life.
3. 16.2.3 Materials F O ~ ~ W O ~ ~
aod Scaffolding
The selectionof materials to be used forfabrication of formwork is governedby job
requirementsand economy.The most commonly used materials are timber, plywood, steel
and aluminium.When the formwork is to be used for small works and that too a few times,
then timber proves to be more economical than steel or aluminium.However,if the
formworkis required to be reused several times likein a multistoreyedbuilding, then the
use of steelor aluminiumis preferred.In case of steel,though the initial cost is very high,
but it proves to be economical when it is used repetitively in large works. Also the erection
and removal of steel formwork are simple and present a better appearanceon removal.
Particularlyin case of structureslikeround columns, carved surfaces,monolithicsewers,
tunnels and sirniliar structure, the use of formworkshould be made as a matter of
expediency.
However, in Indian conditions,timber is still used quitecommonly in smallerworks. This
is due to the fact that it is easily worked and that its use to a degree is traditional. Timber
should preferablybe softwoodusually pine, fir or sprucewhich has been partially
seasoned. Very dry timber will absorbmoisture from wet concrete or atmosphereand
swell,while green timber will shrink. Hardwoodis not normally used as it is expensive,
heavy and difficultto work and nail.When appearanceof finishedcomete isof littleorno
importme,cleansawntimbermay be used,but inview of greatereaseof fitting,the use ofplaned
timber will oftenprove to be ecormmicalboth in time andlabour.
Sizes of forms alsoplay an important role and are linked to the material used for formwork.
The sizes should be based on the criteria givenbelow :
a) If forms are prefabricatedinto panels or sections, it is desirable to fabricate
them in sizes as big as the concretemembers or the sizeswhich the adopted
method of handling will permit. This helps in reducing the labour and time
costs in erection and removal of forms.
b) If the formwork is to be handled manually,then the weight of a singlepanel
should not exceed 35kgs per person.
c) If the forms are to be handled by mechanized method i.e. power equipment,
cranes etc. then the size of formwork is limited by the length of timber
available,the dimensionsof concrete structureand the capacity of the
handling/hoisting equipment. However,timber has been graduallyreplaced by
plywood and today a durable plastic coated material is available to the user. As
timber is becoming expensiveand rare day by day, the need for steel to replace
timber has increased. Aluminium offers a good mediumfor light structural
formwork.In the production of architecturalconcrete,formwork needs special
attention and offersspecialchallenges.For domes,inflatableformsover which
concreteis sprayed is anove) techniquewith an innovativeapproachand with the
range of materials availabletoday, developmentof other forms is a distinct
possibility.
16.3 TYPES OF FORMWORK
There are several types of formwork which are used in construction.Over the years some
special forms like slipform,climbing form and permeable formworkhave alsobeen
developedand are being used. We will now discuss differenttypes of formwork,starting
with the most common i.e. Timber Formwork.
16.3.1 Timber Formwork
Thesizesof timbercommonlyusedforvariouspartsof formworkaregiveninTable 16.1.
Let us now examinea few timber formwork details.
a) Formwork For Columns
Formwork details for a rectangular or square column is given in Figure 16.1.
You may note someimportant features :
i) Columnbox consists of two ends and two sides.
ii) Theheight of each panel is equal to the storeyheight minus the slabthickness
and the floor sheeting.
4. iii) The width betweentwo oppositepanels is kept equql to the actual dimensionof
the columnplus twice the thickness of sheeting.
iv) Yokes are equally spacedon both sides and ends. They project atboth endsby
about 25 cm.
v) A hole is usually provided at the bottom of formwork to remove debrisetc.
before placing the concrete. This cleanouthole is covered before starting the
concreting.
vi) The formcomponentsof column are required to be designed to resist high
pressures which result becauseof continuous fillinglpouringof concrete.
Table 16.1 :Dimensionof CommonlyUsed Formwork Parts
Si.No. Part of Fonnwork Timber Thicknessorsize
1) Sheeting 2.5 to 5 cm
2) Beam and column sides 2.5 to 5 cm
3) Beam bottoms 5 cm
4) Joists 5 cm x 10cm to 7.5 cm x 22.5 cm
5) Ledgers 5 cm x 10cm to 7.5 x 22.5 cm
6) Posts 7.5cmx10cmto15cmx15cm
7) Column Yokes 5 cmx 10cmto 10cmx 10cm.
8) Steeds andWailings 5cmx10cmto15cmx15cm
Sheeting forming
PLAN column sides
ISOMETRIC VIEW
Figure 1
6
.
1 :Formwork forCol-
b) Fonnwork for RCC Beam and Slab Construction
The details of formwork for this arrangementare shown ia Figure 16.2.
5. Rpre1
6
.
2 :Wooden Fonnworkfor MonolithicRC.C. Beam Pnd SlabFloor
The importantfeaturesof this formworkare as follow :
a) The formworkfor slab is generally supportedby means of wooden centering
on the floorbelow.
b) The formworkshouldbe strongenough to support the weight of conterete and
the additional load of approximately 30% to cater for construction loads like
labour, equipment and storageof materials, etc.
c) The formwork forslabmaybe of steel forms while theother components are
wooden.
d) Desired slope shouldbe given in the floorforms itself.
e) Generally, the beam formwork is fabricatedon the ground level and then
hoistedk d placed in position with the slab formworkabove it.
f) Openingsshouldbe provided in the mainbeam formworkto receive the
formwork for secondarybeams.
16.3.2 Steel Formwork
Steel fonnsare manufacturedasproprietaryarticlesby severd firms. While constructional
details vary with the manufacturer,somedetailsare common in them. The forms may
comprisestandard flator curved panel units or be made for a specificpurpose. Generally
speaking,flatpanels maybe adopted to a wide range of usage and the manufacturers
normally supplyaccessories to enable such adaptationsto be made conveniently.
The panel units arenormally made up of steel sheetsreinforced with angle sectionsand are
clipped togetherby keys and wedges or some such similar device to formpanels.
Horizontaland vertical stiffeningis provided by bearers of angle sectionwhich are clipped
to the made up panels (See Figure 16.3).
Rpre1
6
.
3:Sted Fonns
6. cadmeti- T a q a This method of assembly ensuresrigidity and an accurate face. Flat panels are made in a
variety of sizesbut a common size is 60 cm x 60 cm with a range of narrower sections for
use as closures.
The advantagesof steel forms in comparisonwith timber are :
a) They can be easily and rapidly assembledby unskilled labour.
b) They have a long life even with minimumreasonable maintenance.They may
be used upto about 50 times before repair becomesnecessary whereas timber
formworkcannot normally be re-used more than four or five times.
c) May be adapted to a wide variety of usage without alteration.
d) Are non-absorbent.
e) No shrinkageor distortiondue to change in moisturecontent. The main
disadvantagein comparisonwith timber is that initial cost is comparatively
high but this is partly offset by reduced labour charges for assembly. Also
where forms are repeatedly used their cost is less then that of timber forms.
There are severalproprietary steel forms availablein the market. We will describebriefly a
fewjust to illustrate, and this may not be construed as a recommendation and is only for
illustrationandinformation.
I) P -form shuttering
In this type ohhuttering pressed steelsections are used to protect the edges of
plywood shutteringwhich alwaysdeteriorates from the edges. Thus this system
has all the advantagesof plywood shuttering as well as normal steel wall -
form shuttehng as one can use all the accessories of steel shutteringwith P -
form shuttering.
11) Steel Forms
Steelforms for Reinforcedbeam and slab construction. A typical steel
formworkcombinedwith plywood for a reinforcedconcrete slab is shownin
Figure 16.4.
1. 16 mm Thick Ply 2. Steel Truss Called Acrow Spans
3. Floor Fom- 4. 7 5 x 7.5 cm Teakwood Runner
5. Beam Clamp 6. Bracing 7. Steel Adjustable Prop,
Figup 16.4 :Centeringfor Reinforced ConcreteSlabs
In the above figure it can be seen that floor formslslab forms are placed on
Acrow spans (steel truss) for reinforcedconcrete slab construction.,The
adjustablebeam clamp holds timber, plywood or steelfirmly and thus prevents
bulging. This formwork is supportedon adjustable steelprops or telescopic
props.
7. 111) GridDecking System
This system is designed for flat slab beams and slab, waffle and trough floor
construction (SeeFigure 16.5).
figure165:Grid Decking System
The dropheads with their seatingsin raised position are erectedon adjustable
jacks or verticals.Deck beams are securedon the drop head settings.
Floorforms or plywood over infile beams at required spacingare placed
between deck beams andjacks are adjusted to get the required level. The deck
beams drop through 80m
r
n height after strikingdropheads alongwithremoval
of formwork and thus leaving supportto slabs,undisturbed.
IV) WallformSystemof Formwork
The Wallformsystemof formwork with soldiers, walers and clips is a self
supporting system It is availablefor concretingwalls in pour heights such as
1.25 m, 2.5 m, 5 m or more for buildings, water tanks, basement walls etc. One
such system is shown in Figure 16.6.
figure1
6
.
6 :Wdform Clhnbii Steel Shuttering
8. This wallformsystem is either for one sided shuttering or both sided shuttering
with loop anchors or wall ties, embedded in concrete for anchorage.
Another systemhas a basic elementcalled H-16 beam which is I - shaped
plywoodtimber beam. It is versatile,sturdy and handy, dimensionallystable,
uniform in size and possess uniform high strength. For walls, H-16 beams are
combinedwith steel waiers to produce a light weight panel which can be easily
assembledas required. This enables full size plywood sheets to be used as
sheathingwithout the necessityof cutting them into smaller panels. This
minimises the number of sheathingjoints and helps in achieving good quality
concretesurface. The Figure 16.7givenbelow will give you some idea of
differentparts of this system.
I. Plywood 2. H-16 Beam 3. Steel Walers 4. Adjustable Props
Figure16.7 :Wall Formwork
V) Tubular Steel Formwork
This formwork is well illustratedin the Figure 16.8.
The exampleshown above is formwork for barrel shell-roofs. This formwork
consistsof tubular steelfittings and is extensively used for sheet-roof
constructionin developed countries.In this formwork steel sheet is provided at
the top continuingin valley beams to receive the concrete. Adjustablejack
bolts and props are provided to obtain varying heights of shell roofs as well as
of ribs and valley beams.
Curve H.S.Tcc
Steel tube5cm
Figure 16.8 :TubularSteel Formwork for BarrelShell-roofs
9. 16.3.3 ClimbingFormwork
Climbingforms are used for tall structures and consistessentially of a narrow band of
formworkencircling the structures,which is raised as work proceeds.They may be made
up on siteor be specially manufactured.Various proprietary forms are availablein the
I market.
!i a) In most cases of climbingformwork, the height of concrete lift is restricted between 30
j cms to 100cms but certain types allow for continuouspouring in order to produce a
joint free structure.In the latter case the formwork is carried in a yoke suppoded and
t raisedbyjacks resting on rods embedded and left in concreteor on posts erectedon
both sidesof the walls (SeeFigure 16.9).Slipformwork is a good example of climbing
i
formwork.
Figure 16.9 :ClimbingFormwork
b) Steelforms are particularly suitablefor this type of formwork.Two simple
arrangementsof climbing formworkusing steel formsfor thick walls are shown in
Figure 16.10.
Horizontal
liners
Vertical
liners
Wintirs
First set-up
I60 or 120cn lift)
2nd l i f t
First set-up
( 60 or 120cnlif
Win tie Iwp
cut off after
strappmp
Second subsequent d + p
l60cn l i f t s )
3rd l i f t
1
...',.
:
.
. .., .
,
. cmcrete after
' : .
Second and subsquent d-p
( 60 cn l i t ts
Figure16.10 :Climbing Formwork of Steel Forms for Thick Walls
10. C O D S ~ I - I I ~ ~ ~ O I I
Techniques C) A sophisticated type of climbing formwork is shown in Figure 16.11.
This incorporatesa working platform and is fitted with optional accessories like
push-pull struts for aligningthe formwork assembly. It also has rolling mechanism for
side shifting of the formwork assembly to provide working space to fix reinforcement
and other inserts in narrow and deep wall construction. The slip form and anothertype
of climbing formwork are shown in Figures 16.11 and 16.12.
water 2,Sm long. 8Nos.
for 2.5 m height of
Figure~l
6.11 :Climbing Formwork
Form panels, straightor curved, are fitted to sturdy
yokes with working platform,suspended walkways
and safety railingsHydraulicjacks mountedon yoke
beams climb on solidjack rods. The slipform is
available fortapered structuresalso.
Figure 16.12:Slipform
d) Automatic climbing formwork,which is another type of climbing formwork is also.
called self climbing formwork as it does not need any crane for the climbingoperation.
This systemhas certain special featureswhich are enumeratedbelow :
i) This systemhas automaticclimberswhich automaticallyhoist up the formwork
step by step.
ii) Formwork for tall structuresis solved conveniently and crane costs are cut
down and work is speeded up.
iii) The entire work can be performed during the normal day shift and thus costly
night and week-end shiftscan be dispensed with.
iv) Since it provides stationary platform and formwork,it rationalisesreinforcing
and pouring operations.
v) The formworkis designed for safeguardsagainst strong winds and other
eventualities.
vi) The need for scaffoldingis eliminated.
vii) It enables easy and speedy cleaning of form shutters.
viii) Since working space available is sufficient,it also allows better supervision
and qualitycontrol.
ix) Concretingupto 1.5 metre per day is possible.It also allows adjustments for
slope and precision alignments.
Thus, the use of this systemis bound to lower the constructioncosts and result in
higher productivity.In this formwork system the need for slulled labour is less as the
need to make, fix and remove scaffolding is rninimised, which reduces expenses.
A automaticclimbing formwork for constructionof cooling tower is shown in Figure
16.13.The formworkcan be seenat the top of the cooling tower.
11. Figure 16.14 :TravellingFormwork
16.3.5 Permeable Formwork
The Japanesehave pioneered and perfected the systemof permeable formworkfor
verticaUinclined surfacesto improve the durabilityof concrete. The formwork is first
prepared in the conventional manner. The sheetingof formwork can be of plywood or steel.
Now a series of holes are drilled in a grid pattern to facilitatedraining of water and
Figure 16.13 :Automatic ClimbingFormworkfor Cooling Towers
16.3.4 Moving Formwork
Where long lengths of concrete work of constant cross-section have to be constructed,
moving or travellingformwork maybe used with advantage.In such cases a complete
section of formwork is fabricated and assembled and is carriedon some suitableform of
travelling carriage running on railway lines or other suitabletracks.A typical example is
shown in Figure 16.14.
12. T d n i q u a expellingof air when the concreteis placed and vibrate$. Generally the hole diameter is 3
mm and their spacingis 100rnmcentreto centre. Next, a Coven fabric is fixed to the inside
face of the sheathingof the formwork,such thatno water remains trapped in the interstices
between the fabric and the sheathing.For fixing to plywood, staplers may be used while for
steel, glue or adhesiveis used. The concrete mix used with permeableformworkgerferally
has watercement ratios in the range of 0.4 to 0.6. The permeable formworkis designed fm
all pressures as applicabletonormal formwork.
When the concrete is placed in the formwork,high pore water pressure formsin the
concrete in proportion to its depth. But the use of permeableformwork,allowsdissipation
of this pressure by drainingoff water. As a result,pore water in the concretevaries form
high pressure in the core of the concreteto a low pressure at the face of the formwork. This
movement and drainageof water improves the quality of the concretefor a depth of about
150mm from the face of the permeable formwork. The lowered water -cement ratio
results in reduction of permeability of concrete and improvementof surface qualityof
concrete.
16.3.6 Permanent Prestressed Concrete Formwork
Permanent forms are formswhich are left in place, that may or may not become an integral
part of the structuralframework. These forms maybe of rigid type like metal deck,precast
concrete,brick, ferrocement, wood, plastics and some types of fibre board. The flexible
types could be likereinforced waterrepellentcorrugatedpaper or wire mesh with
waterproof paper backing.
Reinforcedconcrete,fibrousconcrete and wood wool concretehave alsobeenreportedto
be used aspermanent formworkto cast structuralmembers such as slabs and beam.
Prestressedconcretecan alsobe used in casting as it offers distinct advantageslikehigher
strengthto weight ratio over plains or reinforced concrete.The use of pennanent formwork
would alsoresult in large savingsin timber or steel forms and also results in savings in
constructiontime.
SibQ 1
a j '~Vhntarc !hc advantages of steel Soi~lis
over tinlbcr forms ?
b) Wri:c a short ~lotc:
on the economy m fo~~~iwork.
L: W:nal nlatcriais are conmionly used in tomiwork'!
di %hat are the constituentsof cost of formnwork?
16.4 REMOVAL AND MAINTENANCEOF FORMWORK
Formwork shouldbe strippedor removed with care so as not to damage the concrete.
Wedges shouldbe slackenedgraduallyto avoid suddenimpositionof loads on the structure.
The strippingtime for different members has been laid down in 13:456-1978which gives
generalguidelinesabout the time of removal of formwork,where ordinaryportland.cement
is used. It statesthat "Forms shallnot be struckuntil the concretehas reached a strength at
least twice the stressto which the concretemay be subjectedat the time of removal of
13. formwork. The strength referred to shallbe that of concreteusing the same cementand F O ~ W O & and Scaffolding
aggregateswith the sameproportions and cured under conditionsof temperature and
moisture similar to those existingon the work. Where possible the formwork shallbe left
longer as it would assist the curing."
It furtherlays down that "In normal circumstances and where ordinary portland cement is
used, formsmay generallybe removed after the expiry of the followingperiods :
a) Walls, columnsand vertical faces 24 to 48 hours as may be
of all structuralmembers decidedby the engineer-in-charge
b) Slabs (propsleftunder) 3 days
c) Beam soffits(props leftunder) 7 days
d) Removal of props under slabs :
1) Spanning upto 4.5 m 7 days
2) Spanningover 4.5 m 14 days
e) Removal of props under beams
and arches :
1) Spanningupto 6 m 14 days
2) Spanningover 6 m 21 days
For other cements,the stripping time recommendedfor ordinaryportland cement may be
suitably modified."
It alsofurther lays down that 'The number of props left under, their sizes and disposition
shallbe such as to be able to safelyc;l-ry the full dead load of the slab,beam or arch as the
casemay be with any live load likely lo occur during curing or further construction."
You may alsoobservefollowinggeneralpoints during stripping
a) Any prising that is necessary, should be done against formwork and not the
concrete.
b) As formworkis stripped,it should be cleaned and properly stacked.
c) All smallparts such as wedges and bolts etc. shouldbe storedimmediately in
separatecontainers.Such a practice reduces loss of material.
d) Steelforms shouldbe greased immediately aftercleaning and before stacking.
Let us now examine another important temporary structure called "Scaffolding".
16.5 SCAFFOLDING
The "Scaffolding" is a temporary structure which is employed in building construction
operationsto supportplatforms for workmen, materials and equipments. Scaffoldingmay
be erected eitheron one or both sidesof the walls. The height of the scaffolding canbe
adjusted as the work progresses.
The Figure 16.15 shows anordinaryscaffolding.Different parts of the scaffolding are
labelledto enable you to identify them.
The variousparts of a scaffoldiilgaregenerally secured by means of rope-lashings, bolts,
etc.
16.5.1 Types of Scaffolding
The different types of scaffoldings which are generallyused :
a) SingleScaffolding
b) Double Scaffolding
c) Ladder Scaffolding
d) CantileverScaffolding
e) SuspendedScaffolding
f) SteelScaffolding and Centering
g) TrestleScaffolding
14. VERTICAL SECT1ON
Figure 16.15 :Scaffoldingand its Various Parts
We will examineonly two of these, i.e. Double Scaffoldingand Stee1Scaffolding.
16.5.2 Double Scaffolding
This Scaffoldingis called Mason's Scaffoldingand is shown in Figure 16.16.
This scaffoldingis strongerthan singlescaffoldingand'does not require to be secured into
the wall and hence no holes are to be ma& in the wall. The first row of standardsare kept
15cm from wall face and the other at 1.2to 1.5maway from the face of the wall. The
putlogs are supportedat both the endson ledgers.
SECTIONAL ELEVATION
Figure 16.16 :Detailsof Double or Mason's Scatiolding with Raking Shore
16.5.3 Steel Scaffoldingand Centering
Details of tubular steel scaffoldingused as centeringfor slabandbeam constructionis
shown in Figure 16.17.
15. W t o m boards at
- - +Jp~qf'"
supports or
(1 braces fl
SECTIONAL ELEVATION
Figure16.17 :Details &TabularSteel ScaffoldingUsed m Centeringfor Slaband Beam Corntruetion
You would have noticed that the constructional details of steel scaffolding are similar to
that of wooden scaffoldingexcept that wooden members arereplacedby steel tubes,plates and
angles and they arejoined by special couplings and screws. The diameter of steel tubes
generally used varies from40 to 60 mm with sheet metal thickness of about 5 m
r
n
Steel Scaffoldinghas several advantages over ordinary timber scaffoldingnamely :
It is suitablefor any height.
Though its initial cost is high, but it is economical in the long run.
Its erection and dismantlingis rapid.
It is strong and durable and has longer life.
Ithas better fie-resisting qualities and higher salvagevalue.
It can be converted into moving form unit by the use of wheels.
16.5.4 U-FrameScaffolding
It consists of right welded frame of two verticals and two horizontals. The various frames
are interconnected by scissor cross braces through plug welded on frames and are locked in
position by spring clips. This imparts very good rigidity and it can be erected even by
unskilled labour.It is ideal for heavy stiuctures,high slabs,bridge girders etc. It is shown
in the Figure 16.18.
Figure 1618 :U-FrameScaffolding
16. cOmtru& Techniques
16.6 SUMMARY
The appearance of the finished structureand the speed with which it can be completed are
greatly dependentupon the efficientconstructionand type of fonns employed. Several
material liketimber,plywood, steeland aluminium are being used in formwork. Several
types of formwork are now available which are efficient, safe and simple to use. In large
and tall structures, moving and travelling formworks are being increasinglyused. A major
technological advancement is the development of slipfonning techniqueand automatic
climbingformwork. Among the recent advancementsare the permeable formwork and
permanent formworks.The questionuppermost in the mind of an engineeris as to whether
a revolutionary change in formwork can be done to evolve a formworkwhich fonns an
integral part of the concreteand adds to its durability.
Steelscaffoldingis becoming most popular, particularly the tubular steel scaffolding
becauseof their light weight, long life and ease of erection. New forms of standardised
steel scaffoldinghave made the task very easy and they help in speedingup the work
without sacrificing safety.
Activity
A largenumber of commercially manufactured formwork and scaffoldingsystems are
now available in India. Compile a data sheetcomprising all details about these systems
for ready reference.
16.7 KEY WORDS
Formwork : Temporary structureto receive wet concrete and hold it in place.
Scaffolding : Temporary structureto supportplatform forworkers, materialsand
equipments.
Stripping : Removal of formwork afteruse.
16.8 ANSWERS TO SAQs
SAQ 1
a) The advantages are :
i) They can be easily and rapidly assembled by unskilled labour.
ii) They have a longlife evenwith minimum reasonable maintenance.
iii) They can be reused upto 50 times or so before repair becomes necessary.
iv) May be adapted to a wide variety of usage without alteration
v) Are non-absorbent.
vi) No shrinkgeor distortion due to change in moisture content.
b) See Section 16.2.2for details of the answer.
c) The commonly used materials are timber, plywood,boards, steel, aluminium
and plastic coated sheets.
d) The constituentsof cost of formwork are :
i) Cost of materials,
ii) Costof labour required for fabrication,
iii) Costof erection and removal of forms, and
iv) Cost of maintenance of forms.
