6. FORMWORK (ACE) 2160601 GTU

1
PREPARED BY : ASST. PROF. VATSAL D. PATEL
MAHATMA GANDHI INSTITUTE OF
TECHNICAL EDUCATION &
RESEARCH CENTRE, NAVSARI.

 Formwork is a mould including all temporary supporting structures, used to shape
and support the concrete until it attains sufficient strength to carry its own weight.
 It should be capable of carrying all imposed dead and live loads apart from its own
weight.

 Formwork has been inuse 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.

 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.

1. Easy removal
2. Economy
3. Strength
4. Rigidity
5. Less leakage
6. smooth surface
7. Light weight
8. Quality
9. supports

1. Easy removal
The design of formwork should be such that it can be removed easily with least
Amount of hammering. The removal of formwork should cause least injury to the
surface or edges of the concrete.
2. Economy
As the formwork does not contribute anything to the stability of the finished
structure, it should therefore, be made economical by reducing the cost through
proper design and construction.
3. Strength
The formwork should be strong enough to withstand all loads coming on it, such as
dead load of concrete and live load during its pouring, compaction and curing. The
loads on formwork should be estimated carefully. The over-estimation of loads result
in expensive formwork and the under estimation of loads results in the failure of
formwork.

4. Rigidity
The formwork should rigid (stiff) enough so that deflection is minimum. For visible
surface in completed the work. the deflection limited to 1/300 of span and for hidden
surface, It is limited 1/150 of span. It should be noted that a rigid formwork will be
robust and stiff enough to allow repeated use.
5. Less leakage
The formwork should be so arranged that there is minimum of leakage through the
joints. This is achieved providing tight joints between adjacent sections of the
Formwork.
6. smooth surface
The surface of the formwork should be smooth, and it should afford easy stripping
This is achieved by applying crude oil or soft soap solution to the inside surface of
formwork.

7. Light weight
The formwork should be as light as possible.
8. 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.
9. supports
The formwork should rest on sound, hard and non-yielding supports.

The following points are to be kept in view to effect economy in the cost of formwork
The plan of the building should simply minimum number of variations in the size of
rooms, floor area etc. so as to permit reuse of the formwork repeatedly.
Design should be perfect to use slender sections only in a most economical way.
Minimum sawing and cutting of wooden pieces should be made to enable reuse
of the material a number of times and the quantity of surface.

1.Plywood
2.Timber
3.Steel
4.Aluminium
5.Plastic

• Formwork can be made out of timber, plywood, steel, precast concrete or fiberglass
used separately or in combination.
• Steel forms are used in situation where large numbers of re-use of the same forms are
necessary.
• For small works, timber formwork proves useful. Fiber glass made of precast concrete
and aluminum are used in cast-in-situ construction such as slabs or members involving
curved surfaces.
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1.Assembly and erection .
2.Concrete placement.
3.Stripping and dismantling.

In concrete construction formwork is commonly provided for the following structural
members.
• Wall
• Column
• Beams
• Slab
• Stairs

• Panel sheathing – It is used to shape the wall and retain the concrete until it sets.
• Studs – to support the sheathing or Wales by forming a framework to keep the forms
aligned and support the studs.
• Braces – It isused to prevent deflection of forms under lateral pressure and keep
the formwork erect.
• Ties and spreaders – These are used to hold the sides of the forms at the correct
spacing.

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• The sheets are supported by vertical studs and horizontal wales. The ties are provided to
maintain the distance between the sheets and to resist the bursting action of concrete.
• The small pieces of timber known as spacers may be used and
they are to be removed as the concrete reaches that level.
• In addition, the wire ties and bolts may be also provided. If bolts are used they are to be
provided with grease so as to make their removal easy after 2-3 days of pouring
concrete.

It consists of the following:
• Side & End Planks
• Yoke
• Nut & Bolts
Two end & two side planks are joined by the yokes and bolts.
It should be rectangular or square in shape.

Beam soffit must be thickened timber or strengthened plywood.
Beam sides 18mm plywood or 25mm boards, with studs (cleats) at 500 to 600mm.
Deep beams (over 600mm) should have walkers and ties.
Use angle fillets in the beam side to soffit joint where possible.
Allowance must be made for height adjustment of the props or false work.
 Erection sequence for constructing beam formworkincludes
Position of sole plates
Marking out and setting heights for false works
Assemble and position props, adjustable head jacks, false works, bearers and spreaders
Construct and erect side walls and beam soffit.
Position of sole plates.

• 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.

• It consists of
– Vertical & inclined posts
– Inclined members
 -- Wooden Planks or sheeting
– Stringer
– Riser Planks

Points to consider when designing stair form work :
Stair formwork must support the weight of concrete.
The weight of the throat of the stair and the steps will have to be supported.
Because of the slope of the stair, some of the force is transmitted sideways.
All formwork must be well tied together to prevent sideway movement.
Consider the finish of the stair treads and type of nosing.
Space may have to be left for purpose made nosing.

• Centering is the temporary structure required to support brick, stone or concrete
work of arch, Dome etc. during its construction .
• The centering choice depends upon several factors like:
• Shape of Arch
• Span of Opening
• Thickness of Soffit
• Material used in arch construction …etc.

Width of the thinner soffit is 10cm. If the width of the soffit is wider than 10 cm. , two
ribs suitably spaced & shaped at
the Top may be used.

• For the construction of big arches, thecentering will be invariably required.
FACTORS:
• Nature & type of arch (i.e. span, rise etc…)
• Foundation conditions
• Depth of water , liability to flood, etc…
• Distance required between support of centering for the passage oftraffic.
• Size & lengths of timber available
• Availability of labour.

1. Timber truss centering
2. Trestle centering
3. Steel truss centering

It is very useful when,
 The arch provided in deep valley.
 The support for centering are to rest in deep water.
 The passage of traffic is required during the construction of arch.

The term “trestle centering” is used to mean that the arch is supported by posts resting
on the ground. Trestle centring can be arranged in a variety of forms, as shown

It is very useful when,
 It is impossible to use trestle type centering
 Depth of water is more
 Arches constructed for heavy flood.

• Method of vertically extruding a reinforced concrete section and
is suitable for construction of core walls in high-rise structures –
lift shafts, stair shafts, towers.
• The formwork rises continuously, at a rate of about 300 mm per
hour, supporting itself on the core and not relying on support or
access from other parts of the building or permanent works.
• Allows for the continuous pouring of concrete into walls of a
structure and only stops when the full required height of the
structure has been reached.
•The height of the formwork is designed in such a way that while
the top of the formwork is being filled by concrete the lowest
layer of concrete poured earlier has already gained an initial set.
When the formwork is moved upwards the concrete that is then
exposed remains firm.

• Assembly can only start once the foundations are in place and the wall starter is in
correct alignment.
• Slip form shuttering is aligned with the help of yokes.
• Horizontal crossbeams connect these yokes.
• Hydraulic jacks are attached to these crossbeams for simultaneous upward
movement.
• Height of the slip form ranges from 1.1 to 1.5 meters.
• Yokes and crossbeams also used to support the working platform.
• Structure should be rigid and shape maintained at all times.
• It is also possible to reduce wall thicknesses as the construction gains height and
arrangements have to be made in the slip form structure that will enable such reduction
at regular intervals.

• Slip form methods of construction can also be adapted to horizontal structures
and are used for paving, canals, and tunnelling.
• The technique is more in use for structures that have continuous walls like silos,
chimneys, and piers for very tall bridges.
• It has also been successfully used for construction of buildings, although this
requires the manner of leaving inserts for openings like doors and windows to be
decided well in advance, as well as also any necessary inserts to support floor
slabs after the walls are constructed.

• A major cost of concrete structure construction is the required formwork to retain the
concrete till it can be safely de-shuttered and be able to support itself and other imposed
loads.
• The formwork needs to be continually removed to newer locations and then re-
erected.
• Continuous use of manpower and lifting equipment like cranes.
• In the case of slip form building, the formwork is erected only once and remains
intact until the entire structure is completed.
• Great reduction in the cost of formwork as well as time saving for re-erection.
• Cost effective
• Saving in to the labour cost otherwise used for intermittent concreting operations.
• The reduction in the movement of formwork and workers also leads to far more safe
working conditions that also make it a major advantage.

• Concrete is continuously protected against loss of moisture and rapid temperature
changes for 7 days
• Unhardened concrete is protected from rain and flowing water
• Prevent plastic shrinkage
• Plastic cracks are filled by injection of epoxy resin.

• DESHUTTERING in simple means, the process of removing the shuttering
(Formwork for Concrete).
• Order and method of removing formwork:
• Shuttering forming vertical faces of walls, beams & column sides should be
removed first. Shuttering forming soffit to slab should be removed next.
• Shuttering forming soffit to beams, girders or other heavily loaded members
should be removed in the end.
• Factors considerd :
• Concreting is done under normal circumstances
• Cement used is Ordinary Portland Cement
• Adequate curing is done
• Ambient temperature is not fall below 15 degree

Time of formwork removal depends on the following factors :
Type of Cement
Rapid hardening cements require lesser time as compared to OPC (Ordinary
Portland Cement)
Ratio of concrete mix
Rich ratio concrete gain strength earlier as compared to weak ratio concrete.
Weather condition
Hydration process accelerates in hot weather conditions as compared to cold and
humid weather conditions.

• 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 levelled by ,allet and loose corners must be
welded.

 For normal works cost of formwork is about 30%-40% of the concretecost.
 For special works cost of formwork is about 50%-60% of the concretecost.
 Formwork cost is controlled by the followingfactors
• Formwork Material cost
• Formwork erecting cost
• Formwork removal cost
• Formwork jointing cost (Nails and Cables)
• Labour charges.

 Formwork failures are the cause of many accidents and failures that occur
during concrete construction which usually happen when fresh concrete is
placed.
 Generally some unexpected event causes one member to fail, then others
become overloaded or misaligned and the entire formwork structure collapses.
 Improper stripping and shore removal
 Inadequate bracing
 Vibration
 Unstable soil under mudsills, shoring not plumb
 Inadequate control of concrete placement
 Lack of attention to formwork details
 Inadequate cross bracing and horizontal bracing of shores
 Forms sometime collapse when their shores/ jack are displaced by the vibration
caused by: movement of workers & equipment on the formwork

 Material used for the construction of formwork must fulfil the specification.
 Formwork is fixed firmly & properly
 Construction area must be protected to prevent of formwork.
 Warning sign must be put up at the area where the formwork is fixed to prevent
entrance of people that may damage the formwork.
 The formwork must be inspected before the concrete is poured.

6. FORMWORK (ACE) 2160601 GTU

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6. FORMWORK (ACE) 2160601 GTU