FORMWORK.pptx

What is Formwork?
• Formwork is a mould including all supporting
structures, used to shape and support the
concrete until it attains sufficient strength to
carry its own weight.
• It should be capable of carrying all imposed
dead and live loads apart from its own weight.
Formwork is commonly made of
• Steel andTimber

• Formwork has been in use since the beginning
of concrete construction.
• New materials such as steel, plastics and
fibreglass are used in formwork.
• Greater attention is being given to the design,
fabrication, erection and dismantling of
formwork
• Formwork is designed according to The ACI
document SP-4.

Qualities of Formwork
• It should be water tight.
• It should be strong.
• It can be reusable.
• Its contact surface should be uniform.
• It should be according to the size of member.

In order to successfully carry out its function, formwork
must achieve a balance of following requirements:
• Containment
• Strength
• Resistance To Leakage
• Accuracy
• Ease Of Handling
• Finish And Reuse Potential
• Access For Concrete
• Economy

• Containment: formwork must be capable of
shaping and supporting the fluid concrete
until it cures.
• Strength: formwork must be capable of safely
withstanding without distortion or danger the
dead weight of the fluid concrete is placed on
it, labour weight, equipment weight and any
environmental loadings.

• Ease of Handling: form panels and units
should be designed so that their maximum
size does not exceed that which can be easily
handled by hand or mechanical means. – In
addition all formwork must also be designed
and constructed to include facilities for
adjustments, levelling, easing and striking
without damage to the form work or concrete

• Economy: All the formwork is very expensive. On
average about 35% of the total cost of any
finished concrete unit or element can be
attributed to its formwork; of this just over 40%
can be taken for material for formwork and 60%
for labour. – The formwork designer must
therefore not only consider the maximum
number of times that any form can be reused,
but also produce a design that will minimize the
time taken for erection and striking

Major objectives considered in
formwork:
➢ Quality
➢ Safety
➢ Economy

• Quality: Forms must be designed and built
with sufficient stiffness and accuracy so that
the size, shape, position, and finish of the cast
concrete are maintained. so that they have
• Safety: Forms must be built sufficient strength
and factor of safety the capable of all
supporting loads.
• Economy: Forms must be built efficiently,
minimizing time and cost.

Requirements of formwork:
• Material should be cheap and re usable,
• It should be practically water proof, so that it should
not absorb water from concrete,
• Swelling and shrinkage should be minimum,
• Strong enough to with stand all external loads,
• Deflection should be minimum,
• Surface should be smooth, and afford easy striping,
• Light in weight, so that easy to transfer,
• Joints should be stiff, so that lateral deformation and
leak is minimum .

Three stages in the process :
a) Assembly and erection
b) Concrete placement.
c) Stripping and dismantling.

Formwork detail for different
structural members
• In concrete construction formwork is commonly
provided for the following structural members.
• Wall
• Column
• Slabs & Beams
• Stairs o Chimneys
• Water tanks
• Cooling Towers

Formwork for Wall
It consists of
Timber sheeting
• Vertical posts
• Horizontal members
• Rackers
• Stakes
• Wedges
➢ After completing one
side of formwork
reinforcement is provided
at the place then the
second side formwork is
provided.

Formwork for Column
It consists of the
following – Side & End
Planks – Yoke – Nut &
Bolts
• Two end & two side
planks are joined by the
yokes and bolts.

Formwork for Slabs & beams
It consistsof
– Sole plates
– Wedges
– Props
– Head tree
– Planks
– Batten
– Ledgers
• Beam formworkrests on
headtree
• Slab form work restson battens
andjoists
• If prop height aremore than 8’
provide horizontalbraces.

FORMWORK FOR STAIRS
It consists of
– Vertical & inclined
posts
– Inclined members
-- Wooden Planks or
sheeting
– Stringer
– Riser Planks

FORMWORK FOR CHIMNEYS
For tall chimneys two
types of forms
techniques are in
generally use in our
country
a) Jump form
b) Slip form

Removal of formwork
• Time of formwork removal depends on the following factors:
Type of Cement
Rapid hardening cements require lesser time as compared to OPC
(Ordinary Portland Cement)
Ratio of concrete mix
Rich ratio concrete gain strength earlier as compared to weak
ratio concrete.
Weather condition
Hydration process accelerates in hot weather conditions as
compared to cold and humid weather conditions

Comparison between Steel and
Timber Formwork
• Steel forms are stronger, durable, and have a longer life
than timber formwork and their reuses are more in
number.
• Steel forms can be installed and dismantled with greater
ease and speed.
• The quality of exposed concrete surface by using steel
forms is good and such surfaces need no further
treatment.
• Steel formwork does not absorb moisture from concrete.
• Steel formwork does not shrink or warp.

Cantilever slab
First free end's support
should be removed.
• And then from right to
left it
should be proceed.
• If we are removing
from the
mid span then it will act
as a
prop cantilever.

Simply supported slab
In simply supported
we have to remove
the support from the
mid span to the
ends.
• To meet the design
behavior.

Maintenance of formwork
• Due to continuous use wooden planks & steel
plates surfaces become uneven and require
maintenance.
• For wooden formwork use cardboard or plastic
fiber board. Bolt hole places must also be
repaired.
• For steel formwork plates must be leveled by
mallet and loose corners must be welded.

Cost of formwork
• For normal works cost of formwork is about 30%-
40% of the concrete cost.
➢ For special works cost of formwork is about
50%-60% of the concrete cost.
➢ Formwork cost is controlled by the following
factors
• Formwork Material cost
• Formwork erecting cost
• Formwork removal cost
• Formwork jointing cost (Nails and Cables)
• Labor charges

Advantages of steel form work
• It can be used for a no. of times.
▪ It is non absorbent.
▪ Smooth finish surface obtained.
▪ No shrinkage of formwork occurs.
▪ Easy to use.
▪ Its volume is less
▪ Its strength is more

LOADS ON FORMWORK
Dead load
▪ Self weight of formwork
▪ Pressure and loads from fresh concrete
▪ Reinforcement
• Imposed load
▪ Construction workers
▪ Stacking of materials
• Horizontal loads
• Environmental loads
▪ Accidental loads
▪ Wind loads

References
• R.C.C Design by B.C.Punmia
• R.C.C Design by H.J.Shah
• Formwork Design Section 1500
• Doka Formwork Design
• Design of safe timber structures by Eva and
Tomi Torrati

FORMWORK.pptx

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FORMWORK.pptx