Formwork

PRESENTATION ON
“FORMWORK”
CONSTRUCTION TECHNIQUES
BY
K.SNEHA
ROlL NO: 131564
M.Tech 1st year

What is Formwork?
o It should be capable of carrying all imposed dead and live loads
apart from its own weight.
o 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.
Formwork is commonly made of
o Steel
o Timber

 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.
Safety:
Forms must be built sufficient strength and factor of safety so that they have
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.
o Wall
o Column
o Slabs & Beams
o Stairs
o Chimneys
o Water tanks
o 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 consists of
– Sole plates
– Wedges
– Props
– Head tree
– Planks
– Batten
– Ledgers
• Beam formwork rests
on head tree
• Slab form work rests on
battens and joists
• If prop height are more
than 8’ provide
horizontal braces.

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

• FORMWORK FOR SPIRAL STAIRS :

• 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
1. Type of Cement
1. Rapid hardening cements require lesser time as compared to OPC
(Ordinary Portland Cement)
2. Ratio of concrete mix
1. Rich ratio concrete gain strength earlier as compared to weak
ratio concrete.
3. Weather condition
1. Hydration process accelerates in hot weather conditions as
compared to cold and humid weather conditions.

• 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.
Cantilever slab

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

• 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

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