FORM WORK & SLIPFORM

FORMWORK
Slipform
1April 19, 2020 VISHNU VIJAYAN- BMCE

INTRODUCTION
• Concrete Formwork is the temporary structure that
supports the fresh concrete and steel during the
construction process within required Strength and
Tolerance
• Formwork for concrete structures has a significant
impact on the cost, time, and quality of a completed
construction project.
• The cost of the formwork may exceed the cost of the
concrete and reinforcing steel.

Contd..
• The structural safety and reliability of formwork is
just as important as that of the building itself.
• Failure of the formwork during construction could
pose obvious safety concerns, not to mention the cost
of ripping out incorrectly placed concrete
• Design values for wall forms, column forms, beam
forms, and footing forms are all different from each
other.
• The form material must also be considered. The type
of wood and the percent moisture are both factored
into the design process.

DEFINITION:
 Its is an artificial support provided below and around the precast or
cast insitu 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.
 Formwork is designed according to The ACI document SP-4.
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April 19, 2020 VISHNU VIJAYAN- BMCE

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.
5

Uses
 Formwork molds the concrete to the desired shape
and size, and controls its position and alignment.
 Using formwork, concrete structures can be
constructed quickly and in the most affordable way.
Formwork substantially lowers the timeline and costs of
the project
 It is used to transfer the temporary external loads.
6

Major objectives considered in formwork:
 Quality
 Safety
 Economy
7

 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..
8

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 .
9

THREE STAGES:
a) Assembly and erection
b) Concrete placement
c) Stripping and dismantling
10

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
11

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.
12

Wall forms:
 Wall forms principally resist the lateral pressure generated by fresh
concrete as a liquid or semi liquid material.
 The pressure can be quite large, certainly many times the magnitude of
live loads on permanent floors.
 So design often involves closely spaced and well-supported members.
 Snap ties, flat ties, loop ties are single use ties usually relatively low
capacity 680 kg to 1450 kg.
 Coil ties, he bolts, she bolts are left embedded in concrete , or it can be
reused.
 The tension capacity of heavy ties around 27,230 kg.
13

14
Wall forms:

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.
15

Column forms:
 Column-forms materials tend to vary with the column shape.
 Wood or steel is often used with square or rectangular
column.
 Round column forms more typically pre manufactured in a
range of standard diameters, are available in steel, paper
board, and fiber reinforced plastic.
 Round column are more structural efficient compared to square,
since the internal pressures can be resisted by the hoop
membrane.
 Round steel forms are generally used for larger columns and
bridge piers and come in diameters about 0.36m to 3mts.. 16

Formwork for columns

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.
19

Lintel or Beam Formwork:
20

FORMWORK FOR SLAB:
21

FORMWORK FOR STAIRS:
• It consists of
– Vertical &
inclined posts
– Inclined members
– Wooden Planks or
sheeting
– Stringer
– Riser Planks
22

 The sheathing or decking for deck slabs is carried on
cross-joists which are in turn supported on raking
ledgers
 The ledgers are generally of 7.5cm x 10cm size .
 The cross- joists may be 5cm x 10cm size
 The riser planks are 4-5 cm thick and equal to the
height of riser
 The riser planks are placed after the reinforcement is
placed in position
23

24

25

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

Jump Form:
 In this type jacking bars are either cast in concrete
or else are carried in tubes which are cast in
concrete.
 After casting a lift, concrete is allowed to set and
then the forms are raised by jacks and the next lift
is cast.
 Jacks are usually placed about 2m apart and are
designed.

28
Jump Form:

SLIP FORM:
 The slip form method of concrete construction is
used for forming both horizontal and vertical
concrete structures.
 It often used for forming highway pavements as
continuous operation.
 Slip form methods is also been used for forming
various types of vertical concrete structures.
29

30
SLIPFORM

31
SLIPFORM

32

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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.

Time of Removal of formwork:
Sr
.
N
o
Structural Member
OPC
(Ordinary
Portland
Cement)
Rapid
Hardeni
ng
Cement
1 Beam sides, walls &
Columns
2-3 Days 2 Days
2 Slab (Vertical Supports remains
intact)
4 Days 3 Days
3 Slab (Complete Formwork
removal)
10 Days 5 Days
4 Beams (Removal of Sheeting,
Props remains intact)
8 Days 5 Days
5 Beams & Arches (Complete
formwork removal) (up to 6 m span)
14 Days 5-8 Days
6 Beams & Arches (Complete
formwork removal) (more than 6 m
span)
21 Days 8-10 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.
36

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.
37

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.
38

LOADS ON FORMWORK:
Formwork is subjected to following loads:
a) Dead weight of concrete
b) Hydrostatic pressure of the concrete
c) Live load due to working laborers
d) Impact effect at the time of pouring concrete into
the formwork
e) Vibrations transmitted to formwork during
pouring concrete
39

FORMWORK DESIGN
Guiding points in the Design of formwork
 For design purpose, temporary live load due to labor and
equipment including impact may be taken from 3700N/m2
to 4000N/m2
 Dead weight of wet concrete (26000 N/m3)
 Planks or boards used to form the vertical facing of the
columns or walls is known as sheathing whereas those
used for floor slabs are called decking
40

 The hydrostatic pressure due to fluidity of concrete in the initial
stages of pouring depends upon several factors such as amount
of water, size of aggregates, rate of pouring etc.,
 The hydrostatic pressure is maximum at the time of pouring, but
after some time it starts decreasing, as concrete starts setting and
hardening. This pressure is mainly dependent on the depth of
concrete poured before it starts setting
 Deflection of the sheathing and joists should be limited to a
maximum value of 2.5mm
41

Contd...
 The minimum wind design pressure q not less than 15
psf and bracing should be designed for at least
w =46 kg/ft- length applied to the top
 The minimum lateral load w, for design of bracing
system would be greater than,
q .(h/2) or 46 kg/ft
42

Contd...
For design practice the maximum pressure is given
by:
p = wh
Where,
p => lateral pressure of concrete,
w => unit weight of concrete,
h => depth of fluid or plastic concrete.
43

Contd...
For horizontal pressure of concrete is given by:
For walls constructing R less than 2.1m/hr;
p =150+9000(R/T)
For walls constructing R varies from 2.1m/hr to 3m/hr;
p = 150+(43,400/T)+2800(R/T)
For columns 3m/hr;
p = 150+9000(R/T)
Where, R => rate of vertical placement,
T => time for placement.
44

DESIGN OF SLAB FORMWORK:
Design of slab forms can be summarized in the following design steps:
 Step 1: Estimate design loads
 Step 2: Determine sheathing thickness and spacing of its supports (joist
spacing)
 Step 3: Determine joist size and spacing of supports (stringer spacing)
 Step 4: Determine stringer size and span (shore spacing)
 Step 5: Perform shore design to support stringers
 Step 6: Check bearing stresses
 Step 7: Design lateral bracing
45

REFERENCES
• "Emerging Trends in Formwork and Scaffolding", CE & CR, September 92,
Pg.46-49 2. David W. Johnston, P.E., Ph.D. Chapter no.7-Design and
Construction of Concrete Formwork,
• 3. Detroit, Mich. AC1 Committee 347R-94 (1994), "Recommended practice
for concrete formwork." Amer. Concrete. Inst.,
• 4. Basher Aiami -1999, “Analysis of Construction Loads on Concrete
Formwork”.
• 5. Sonjoy Deb, B. Tech, Civil Associate Editor; “Advanced Formwork and its
Management Systems for Speedy Construction of Buildings”.
• 6. Gardner, NJ. (1980),"Pressures of concrete on formwork" ACIJ. 77(4),
279-286.
• 7. Gardner, NJ. (1985), “Shoring reshoring and safety." Concrete
International: Design & Construction, 7(4),28-34,
• 8. “Building Formwork". Building construction By B.C. Punmia (2008
edition).
• 9. "Formwork & Scaffolding, Steel Scaffolding, Centering, Formwork", CE
& CR, July 1998, Vol. 11, No. 7, Pg. 57-60.
• 10. "Emerging Trends In Formwork And Scaffolding", CE & CR, Sep 92,
Pg.46-49. 11. "Construction Equipment "CE&CR, Mayl992, Pg.50 -52. 46April 19, 2020 VISHNU VIJAYAN- BMCE

Thank you ..

FORM WORK & SLIPFORM

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