Formwork, by prof. sagar raut

BUILDING CONSTRUCTION AND MATERIALS
BY:-
PROF. SAGAR R. RAUT
ASST. PROFESSOR
CIVIL ENGINEERING DEPARTMENT
JAGADAMBHA COLLEGE OF ENGINEERING AND TECHNOLOGY,
YAVATMAL

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 Stripping of formwork
 Formwork is designed according to The IS
standards for formwork.

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
Requirements of Formwork

• 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
25% 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.

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
.

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.
Major objectives considered in formwork:

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

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.

• 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 Slabs & beams:

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

• FORMWORK FOR SPIRAL STAIRS :

• Removal of formwork:
Time of formwork removal depends on the following
factors
1. Type of Cement
Rapid hardening cements require lesser time as compared
to OPC (Ordinary Portland Cement)
2. Ratio of concrete mix
Rich ratio concrete gain strength earlier as compared to
weak ratio concrete.
3. Weather condition
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 20%-30% 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

Formwork, by prof. sagar raut

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