Formwork

General
 For the different construction activities like
 Brick work above 5 ft
 Surface finishing works like plastering, painting, walling
etc.
 Renovation, repair and alteration works.
 Roof and slab pouring
Some temporary nature supports and structures are required
like
 Formwork (Supporting Structure)
 Scaffoldings (arrangement for working plate forms)
 Shoring (supporting method for unsafe structure)
 Underpinning (Method of strengthening an existing
structure’s footing)

Form work
 Definition
 Qualities of formwork
 Types of formwork
 Formwork detail for different structural
members
 Removal of formwork
 Maintenance of formwork
 Cost of formwork
 Advantages of steel form work

Definition
 Its is an artificial support provided below and around
the precast or cast in situ concrete work.
 Formwork is commonly made of
 Steel
 wood
 Formwork construction & casting is of prime
importance in concrete industry. It share a
significant amount of concrete cost. (20% to 25%).
 When concrete has reached a certain required
strength, the form is no longer needed & removed.
The operation of removing the form work is known
as stripping.

Qualities of formwork
 It should be according to
IS 456-2000.
 It should be practically water proof so
that it should not absorb water from
concrete.
 It should be strong.
 It can be cheaper & reusable
 It should be according to the size of
member.

Qualities of formwork
 It should be with minimum shrinkage &
swelling.
 It should be stiff enough against it’s
deflection, buckling under load.
 Its contact surface should be uniform.
 It should be light in weight

Types of formwork
 Formwork are mainly of two types
 Steel formwork
 Wooden formwork
 Steel formwork is made of
 steel sheets
 Angle Iron
 Tee Iron
 Wooden formwork consists of
 Props
 Planks battens
 Ledgers
 sheeting

Causes of failure
 Overloading of any props when
sufficient number or size of props not
provided.
 Failure of shuttering due to excessive
vibrations of needle surface vibrators.
 Failure due to improper supervision,
inadequate design/ planning of
shuttering, centering & concreting
activity.

Causes of failure
 Failure due to dislocation of props or
bracing due to careless movement of
labours having access below the
formwork of slab or beam.
 Failure due to insufficient cross
bracing. Cross bracing improve the
stiffness of props against buckling.

Formwork detail for different
structural members
 In concrete construction formwork is
commonly provided for the following
structural members.
 Foundations
 Wall
 Column
 Slabs & beams
 Stairs

Formwork for Foundations
 Wall foundations
 It consists of
 Plywood
Sheeting
 Struts

Formwork for Foundations
 Column
Foundations
 It consists of
 Side Supports
 Side Planks
 Cleats
Side Support
Side Planks
Cleats

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.
Vertical Posts
Struts

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
Riser Planks

Removal of formwork
Time of formwork removal mainly 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.

Stripping Time
Sr.
No.
Structural Member Stripping Time
1 Beam sides, walls & Columns 1-2 Days as decided by
Engineer-in-charge
2 Slab Soffits (props left under) 3 Days
3 Beams Soffits (props left under) 7 Days
4 Removal of props to slabs:
i) Spanning up to 4.5 m
ii) Spanning over 4.5 m
7 Days
14 Days
5 Removal of props to Beams & Arches:
i) Spanning up to 6 m
ii) Spanning over 6 m
14 Days
21 Days

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 numbers 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.

Formwork

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