Types of Formwork
Types of Formwork
Types of Formwork
(SHUTTERING)
Timber is the most common material used for formwork. The disadvantage with
timber formwork is that it will warp, swell and shrink. Application of water
impermeable cost to the surface of wood mitigates these defects.
6. The formwork should be set accurately to the desired line and levels
should have plane surface.
7. It should be as light as possible.
8. The material of the formwork should not warp or get distorted when
exposed to the elements.
Economy in Formwork
The following points are to be kept in view to effect economy in the cost of
formwork:
Formwork can be made out of timber, plywood, steel, precast concrete or fibre
glass 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. Fibre glass made of pre-cast concrete and
aluminium are used in cast-in-situ construction such as slabs or members
involving curved surfaces.
Timber Formwork:
It should be
1. well seasoned
2. light in weight
Timber used for shuttering for exposed concrete work should have smooth and
even surface on all faces which come in contact with concrete.
Plywood Formwork
Resin bonded plywood sheets are attached to timber frames to make up panels
of required sizes. The cost of plywood formwork compares favourably with that
of timber shuttering and it may even prove cheaper in certain cases in view of
the following considerations:
Steel Formwork
This consist of panels fabricated out of thin steel plates stiffened along the
edges by small steel angles. The panel units can be held together through the
use of suitable clamps or bolts and nuts. The panels can be fabricated in large
number in any desired modular shape or size. Steel forms are largely used in
large projects or in situation where large number reuses of the shuttering is
possible. This type of shuttering is considered most suitable for circular or
curved structures.
1. Steel forms are stronger, durable and have longer life than timber
formwork and their reuses are more in number.
2. Steel forms can be installed and dismantled with greater ease and
speed.
Construction of formwork:
3. Provision of camber
1. Shuttering forming the vertical faces of walls, beams and column sides
should be removed first as they bear no load but only retain the
concrete.
2. Shuttering forming soffit of slabs should be removed next.
Rapid hardening cement, warm weather and light loading conditions allow early
removal of formwork. The formwork should under no circumstances be allowed
to be removed until all the concrete reaches strength of atleast twice the
stresses to which the concrete may be subjected at the time of removal of
formwork. All formworks should be eased gradually and carefully in order to
prevent the load being suddenly transferred to concrete.
Figure 3(b): Details of timber formwork for square or rectangular RCC column
Figure 4: Sectional plan showing details of timber formwork for an octagonal
column
Figure 5: Details of formwork for stair
Figure 6: Timber formwork for RCC wall
Table: Period of removal of formwork