The form work is a temporary ancillary construction used as a mould for the structure, in which concrete is placed and in which it hardens and matures. Cost of form work- 20 to 25 % of the cost of structure in building work

1. Prepared by
Prof. Ashish Makwana
Civil Engineering Dept. - MEFGI
1Prof. Ashish Makwana

2. 2Prof. Ashish Makwana

3. PRESENTATION
OUTLINE…
• Form work for R.C.C. wall, slab, beam &
column
• Centering for arches of large spans and dams
• Design features for temporary works
• Slip formwork
• False work for Bridges
3Prof. Ashish Makwana

4. FORM WORK
• The form work is a temporary ancillary construction
used as a mould for the structure, in which concrete
is placed and in which it hardens and matures.
• Cost of form work- 20 to 25 % of the cost of
structure in building work
4Prof. Ashish Makwana

5. FORMWORK FOR CONCRETE
STRUCTURES SHOULD BE
• Strong enough to resist the pressure or the weight
of the fresh concrete plus any constructional live
loads.
• Rigid enough to retain the shape without undue
deformation.
• Economical in terms of the total cost of the forms
and the concrete surface finishing when required.
• Sufficiently watertight to avoid leakage at the
joints.
5Prof. Ashish Makwana

6. 6Prof. Ashish Makwana

7. 7Prof. Ashish Makwana

8. FORMWORK ECONOMY
• Design the formwork to provide adequate but not
excessive strength and rigidity.
• Fabricate the forms into modular sizes to provide
more reuses without refabricating when practical.
• Prepare working drawings prior to fabricating the
forms.
• Prefabricate form sections on the ground rather than
on scaffolding.
• Use the most economical formwork material
considering the initial cost and reuses.
8Prof. Ashish Makwana

9. FORMWORK ECONOMY (continued..)
• Use no more nails than are needed to join the forms
together safely.
• Remove the formwork as soon as it is permissible.
• Clean and oil forms by using releasing agent after
each use.
• When it is permissible install construction joins to
reduce the total quantity of form material required
and permit the carpenters to work more
continuously.
9Prof. Ashish Makwana

10. FORMWORK MATERIALS
1. Timber 2. Metals 3. Plastics
10Prof. Ashish Makwana

11. FORMWORK TYPES (BY SHAPE)
11
Wall Formwork Slab Formwork
Beam formwork
Column
Formwork
Prof. Ashish Makwana

12. 12
FORM WORK FOR R.C.C. WALL
Prof. Ashish Makwana

13. FORM WORK FOR
R.C.C. WALL
13Prof. Ashish Makwana

14. FORM WORK FOR R.C.C. WALL
• Wall formwork is a simpler than for other concrete
units as the actual forces against it are less, most of
the load being carried vertically downwards.
• The panels at both sides are held in position by
ties.
• Ties are also used as spacer, arranging wall
thickness.
• WaII support systems are usually sloping props
at satisfactory intervals.
14Prof. Ashish Makwana

15. 15
FORM WORK FOR COLUMN
Prof. Ashish Makwana

16. FORM WORK FOR COLUMN
• Column formwork is made usually with either timber
or metal panels.
• The principle is to create an enclosed box with
frames at the exact size of the column and fix it
tightly on the kicker left from base or at the last
stage of column concreting.
• The box is held in position by steel column clamps
or bolted yokes and supported by timber studs or
props.
16Prof. Ashish Makwana

17. 17
FORM WORK FOR R.C.C. SLAB
Prof. Ashish Makwana

18. FORM WORK FOR
R.C.C. SLAB
• Floors require a large area of formwork to be
provided usually from beam to beam.
• Timber floor formwork consists of timber boards or
plywood sheets supported on a framework and
resting on a series of timber joists.
• Again timber and metal props can be used for
vertical supports.
• Metal panels can be used and bolted or clipped
together and held in place by a system of metal
beams or a tabular scaffold system.
• Adjustable props need for levelling purposes.
18Prof. Ashish Makwana

19. 19
FORMWORK FOR R.C.C. BEAM
Prof. Ashish Makwana

20. FORM WORK FOR
R.C.C. BEAM
• Beam formwork consists of open through section
and because it is not closed at the top requires
more supporting framework to restrain the sides.
• The supports need to be maintained to the soffit and
also provide lateral support to the sides.
• In timber this is done by the use of a headtree
across the top of a vertical member.
• Metal panels are used with corner pieces, but
timber headtrees are needed for vertical support.
20Prof. Ashish Makwana

21. No Description of structural member
Period of
time
1
Walls, columns and vertical sides of
beams
1 to 2 days
2 Slabs (props left under) 3 days
3 Beam soffits (props left under) 7 days
4
Removal of props to slabs
(a) For slabs spanning upto 4.5 m 7 days
(b) For slabs spanning over 4.5 m 14 days
5
Removal of props to beams and arches
(a) Spanning upto 6 m 14 days
(b) spanning over 6 m 21 days
21
Table 1: Period of removal of formwork
Prof. Ashish Makwana

22. CENTERING FOR ARCHES OF
LARGE SPANS AND DAMS
• Centering is a type of falsework: the temporary
structure upon which the stones of an arch are laid
during construction.
• Once the arch is complete, it supports itself, but until
the keystone is inserted, it has no strength and
needs the centering to keep the voussoirs in their
correct relative positions.
• A simple centering without a truss is called a
common centering. The cross piece connecting
centering frames are called a lag.
22Prof. Ashish Makwana

23. 23
The original Blackfriars Bridge, London,
under construction in 1764
Prof. Ashish Makwana

24. DESIGN FEATURES FOR
TEMPORARY WORKS
• Strength: Forms and shutters have to be designed
to support dead weight, live load and hydrostatic
pressure. Sheathing must be rigid enough to resist
bulging.
• Speedy erection and dismantling: The formwork sho
uld be simple to remove without causing damage to
the concrete.
• Tightness of joints: The liquid retaining properties
the formwork must be adequate to prevent leakage
of cement and fine aggregate from the concrete.
24Prof. Ashish Makwana

25. DESIGN FEATURES FOR TEMPORARY WORKS (continued..)
• Rigidity: Brace formwork and support to ensure
no movement may take place under wind pressure,
or when the concrete is being placed and vibrated.
• Ease of handling: Forms and shutters must be of a
size and weight that can be handled by the labour
and plant available on site.
• Removal of debris: Provide all formwork with special
cleanout holes to allow for the removal of sawdust, s
havings, and other debris from the bottom of the for
mwork before the pour begins.
25Prof. Ashish Makwana

26. DESIGN FEATURES FOR TEMPORARY WORKS (continued..)
• Reuse:
– Design for unit construction, if possible, so that
at you can strike and reuse as soon as possible.
– Use clamps, wedges, and similar devices to hold
sections of formwork in place.
– Avoid nailing as much as possible, nail holes and
bruising of the timber will spoil
formwork for further use.
– The formwork material must be durable and capa
ble of producing a good surface finish.
26Prof. Ashish Makwana

27. SLIP FORMWORK
• This is a form which is continually being moved
upwards, or sideways, as the concrete is being
poured.
• The rate of movement is regulated so that the forms
leave the concrete only after it is strong enough to
retain its shape and support the weights imposed on
it.
• Vertical structures such as chimneys (Huntly Power
Station) and cooling towers (Ohaaki Thermal Power
Station) are often done this way.
27Prof. Ashish Makwana

28. 28
SLIP FORMWORK
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29. 29
SLIP FORMWORK
Prof. Ashish Makwana

30. FALSEWORK FOR BRIDGES
• Falsework is temporary structure or framework used
in construction to support materials, equipment, or
formwork.
• Most falsework is vertical, supporting beams and
slabs. Falsework must be engineer designed.
• As well as supporting the weight, allowance must
made for sideway pressures such as wind, stacks
materials causing eccentric loading, props out of
plumb, formwork being struck by machinery or crane
loads.
30Prof. Ashish Makwana

31. FALSE WORK FOR BRIDGES (continued..)
• Falsework can be:
– timber;
– scaffold tube with adjustable screw jacks, top or
bottom, or both;
– proprietary prop such as Acrow prop;
– proprietary braced frame such as Acrow shore;
– proprietary floor centre (a telescopic beam);
– proprietary beam clamps such as Acrow beam
clamp which combines formwork and falsework.
31Prof. Ashish Makwana

32. FALSE WORK FOR BRIDGES (continued..)
SETTING UP FALSEWORK
• Base must be level and firm. A sole plate is
preferable.
• Props and frames must be placed as per design.
• Place props centrally under members
• Brace falsework in two directions
• Floor centres must have full bearing for the end
tongues.
• Beams must be centred over props to prevent
eccentric (out of line) loading.
32Prof. Ashish Makwana

33. 33
FALSEWORK
Prof. Ashish Makwana

34. THANK YOU
34Prof. Ashish Makwana