Formwork is a temporary structure used to contain wet concrete until it is cured sufficiently to stand on its own. It supports the concrete and maintains its shape. Common materials used are timber, plywood and steel. Formwork must be strong, rigid, braced and water tight. It supports live and dead loads and maintains shape during construction. Formwork is designed based on the type and location of concrete element being cast. Proper formwork design and construction is important for safety and to produce high quality concrete surfaces.

1. BY: CHAKAMBA JOHN

2.  Is a temporary support to pre-cast or in-situ concrete
structures.
 Is the surface, support and framing used to define the shape
of concrete until it is self-supporting.
 It holds the concrete until it has set and can stand on its own
and it maintains the required shape.
 Includes :
 Form on or within which the concrete is poured.
 The supports which carry the forms and the concrete.
 The bracing which may be added to ensure stability as well as
foundations and footings.

3.  It is used for Concrete :
- Lintels.
- Window sills.
- Columns and beams.
- Decking, floors and roofs.
- Retaining walls, stairs, drains.
- Reinforced concrete walls.

4.  Any temporary structure that is used to support a permanent
structure, material, plant, equipment and personnel until the
construction of permanent structure has advanced to the
stage that it is self-supporting.
 Includes:
 Foundations, footings and all structural members supporting
the permanent structural elements.
 Commonly used to support spanning or arched structures,
such as bridges, while they are being constructed.

5.  All formwork must be:
 Sufficiently strong and rigid to support the dead load of the
concrete.
 Designed to allow for the temporary live load of workmen,
wheelbarrows and tamping operations.
 Easy to strip after concreting.
 Constructed within reasonable cost limits.

6.  It should :
 Support both live and dead loads that is, weight of wet
concrete and its reinforcement, weight of workers and their
equipment as well as force of wind and rain.
 Be rigid, water tight, braced and tied together so as to
maintain position and shape during all construction activities.
 Be constructed in such a way that it can be removed easily and
safely, without damaging formed concrete.
 If to be re-used, retain formwork strength during design so as
to minimise deterioration of materials through use and
handling.

7.  Withstand the force of internal or external vibration during the
consolidation of concrete.
 Have smooth surfaces and avoid warped timbers which may
make the surfaces of concrete uneven.
 Be Constructed and dismantled after use so that it is capable
of being re-used and this is ensured by coating internal
surfaces with non-staining oil, white wash or soft soap to
permit easy striking off.

8.  Designers should consider the work practises necessary to
carryout erection and dismantling of the formwork as well as
identifying health and safety risks and controls at the design
stage.
 Possibility of using designs that do not require in-situ formwork,
such as tilt-up or pre-cast concrete elements that may be
constructed elsewhere and lifted into position.
 Method and sequence of erecting and dismantling the formwork
or false work and its supports as well as related risks especially
manual handling.
 Provision of safe access to and egress from the work areas on
and around the formwork.
 Minimizing the working heights for persons erecting and
dismantling.

9.  Guardrail systems including toe-boards, perimeter safety
screens, scaffolding or other means should be installed when
working at heights.
 Fall arrest systems including safety lines can be installed if
required.
 Formwork drawings should include details of formwork,
formwork joints, sealing procedures, ties, size and spacing of
framing and details of any proprietary fittings or systems
proposed to be used.
 Details of the construction and erection sequence should be
included on the drawings,

10.  Choice is influenced by economy and necessity or both.
 Materials commonly used are timber, plywood and steel.
 Are used either separately or jointly.
 Steel formwork
 Merits
 It is durable and can be used as many times as necessary.
 It gives a smooth and better surface finish of concrete.
 It is not liable to warp.
 It is more economical than timber where repetitive work is
necessary.
 Speed of erection with fewer workmen required to
assemble it onsite.

11.  Demerits
 The initial outlay of money is great.
 It is easily dented.
 It is easily affected by rust under humid conditions.
 Timber formwork
Merits
 It is adaptable.
 It is relatively cheap.
 It is more economical than steel where work is non-
repetitive.
 It can be found locally.

12.  It is susceptible to insect and fungal attack.
 It warps, especially when it is not well seasoned.
 It is not good for repetitive work.
 Timber
 Timber for formwork should be neither too dry nor too wet.
 If too dry the timber will absorb water from the concrete
and swell resulting in distortion or decay.
 If too wet shrinkage may result especially during hot
weather which might result to warpage or cracking.
 The normal moisture content of timber used for formwork
should be 20 %.

13.  It is used where a large area of exposed concrete is to be
constructed, for instance walls.
 Merit
 The elimination of joint marks.
 If carefully fixed on site, the finished concrete does not
require further treatment

17.  It is also known as a column box.
 Consists of vertical boards which have battens nailed across
them.
 The battens are called cleats usually 32mm; and the boarding
is called sheeting usually 25mm thick.

18.  Cleats used at the bottom are usually larger so as to
withstand the pressure which is exerted by the weight of the
concrete.
 The sides of the box are secured firmly together by means of
yokes of about 50 by 75mm which may be replaced by use of
sash clamps.
 The column box should be located against a 75mm high
plinth or kicker which has been cast monolithic with base or
floor.

19.  The reinforcement rods and stirrups must be set and well
plumbed up before erecting the column.
 The box is held in position by means of braces fastened to
sole pieces on the floor.
 If the corners of the columns are to be shaped, triangular
fillets or mouldings of the desired shapes are nailed to the
corners of the formwork.
 Concrete is poured as soon as the form base has been
cleaned.

20.  Vertical mould- resist considerable horizontal pressures in
the early stages of casting.
 Kicker – accurately positions the formwork onto the base or
floor. Also prevents the loss of grout
from the bottom edge of the form.
 Soldiers – vertical studs used to strengthen panels forming
the column sides.

21.  Cleats – horizontal battens used to strengthen panels
forming the column sides or mould.
 Margin piece – piece of plank fixed around the opening of a
cut out to provide sufficient bearing for the beam boxes.
 Yokes – pieces of timber used to firmly secure the sides of
the box together.

22.  Yokes – collars of timber or metal used to hold together
column forms timber yokes are purpose made whereas
steel column clamps are adjustable within limits of the
blades.
 Spacing of yokes and clamps should vary with the
anticipated pressures, the greatest occurring at the base of
the column box.

23.  Variance of actual pressure :
a. Rate of placing
b. Type of mix being used- generally the richer the mix the
greater the pressure.
c. Method of placing- if vibrators are used pressures can
increase up to 50 % over hand placing and compacting.
d. Air temperature – the lower the temperature the slower is
hydration process and consequently higher pressures are
encountered.

26.  Consist of two side boards, soffit board and a head tree.
 Two side boards 32mm thick are tongue and grooved and secured
by cleats of 32 by 150mm which are placed at 1200mm centres.
 The soffit boards are thicker than the side boards since they bear
the greater part of the weight of the concrete.
 The soffit board rests directly on the head tree.
 The head tree of 75 by 100 mm timber is placed centrally on a
prop
 The column box may also provide support to the beam box in
framed buildings.

27.  The head tree is secured firmly to the props by braces.
 The props rests on a wedge which in turn rests on a sole
plate.
 Functions of wedge
 To allow the props to be removed easily by knocking out the
wedge when dismantling the formwork.
 To help in achieving the required height.

29.  Some concrete lintels are pre-cast while some are cast in-situ.
 In-situ casting:
 Consist of two side boards and a soffit board which are
sometimes supported by the jambs and, if necessary
immediately between the jambs by wooden posts on a pair of
folding wedges.
 Walls are normally built to lintel level before setting lintel
formwork.

30.  A racking back of about 225 mm on the wall will provide
space where the concrete lintel will rest.
 The soffit rests on the head tree of the props.
 Props are cut little less than the height of wall but required
height will be obtained by striking sole pieces and folding
wedges into the base of the props.

31.  The side boards are placed so that they are flush with the
wall.
 Boards are held by struts nailed to the head tree or by sloping
struts firmly secured to the ground.
 Sometimes side boards are held together by cross-battens
nailed on the top of the side boards at suitable intervals.

34.  Formwork failures are the cause of many accidents and
building failures that occur during concrete construction,
usually when fresh concrete is being placed.
 Generally some unexpected event causes one member to fail,
then others become overloaded or misaligned and the entire
formwork structure collapses.

 The main causes of formwork failure are:
 1. improper stripping and shore removal

35. 2. inadequate bracing
3. vibration
4. unstable soil under mudsills (A plank, frame, or small
footing on the ground used as a base for a shore or post in
formwork), shoring not plumb
5. inadequate control of concrete placement
6. lack of attention to formwork details

36.  It is one in which the form is left as an integral part of the
structure.
 Becomes apparent when pouring concrete into the ground
 Can be utilised as the facing materials of in-situ reinforced
concrete.
 They can be of two types participating and non-participating.
 The materials used for this form must be durable and of
sufficient strength.
 Commonly used materials include polyvinyl chloride,
galvanised coiled, fabricated steel.

37.  low cost of transportation and installation,
 precise form design,
 maximum flexibility,
 greater durability with reduced long term maintenance and
 Versatile.
 DISADVANTAGES
 high initial cost of design and installation
 lack of familiarity for installation and maintenance