FORMWORK

Introduction:

The term ‘formwork’ includes the actual material contact with the concrete, known as form

face, and all the necessary associated supporting structure.

Formwork is a die or a mould including all 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 can be made out of a large variety of materials. Depending upon on the different

materials it can be divided into the following categories. Such as –

1. Timber formwork

2. Plywood formwork

3. Steel formwork

4. Aluminium formwork

5. Plastics

The material most commonly being used to date is timber. However, due to the depleting forest

reserves and increasing cost of timber the use of alternate materials such as plywood and steel

has become prominent. More recently, materials such as plastics and fiberglass are also being

used for pre-fabricating formwork. The type of material to be used depends on the nature of

construction as well as availability and cost of material.

There are different types of formwork available for different purposes. Generally, the formworks

for vertical concreting are called wall forms and those for horizontal concreting are called slab or

floor forms. The various types of formwork are available today. Such as-

a. Climbing formwork

b. Sliding formwork

c. Permanent formwork

d. Special formwork etc.

Scope:

Formwork is used to give different shapes and sizes as needed in the construction.

It is needed to contain the concrete with the reinforcement to adjust with it.

It is also being treated as a support for all our required construction.

For rounded wall , formwork is constructed.

Procedure:

The construction of formwork generally involves the following operations.

i. Propping and Centering

ii. Shuttering

iii. Provision of chamber

iv. Cleaning and surface treatment

In a building construction formworks are done generally for :-

stairs

column

beam and slab

For the stairs, at first the timber as a flight is placed from the floor level to the ‘landing’ for stair

bottom. Then the landing as well as another flight is placed one landing to another. These all

timbers are supported by the bamboo pieces and and small pieces of timber to connect with the

flight and the landing. Then the sides are being attached. Now the reinforcement bars are laid

down as the design is made. Afterwards, for the shape of the steps , the risers are jointed between

the timber sides keeping a distance from the riser’s bottom to the flight surface.

Fig: Formwork of stair including riser,sides,flight

For the column, steel shutter is used covering the reinforcement. Timber is also can be used for

shuttering. These shutters are supported by the steel props as well as with some steel rods which

are connected with ‘Turn’ . The shutterings are attached with bolt but if timber is used for

shuttering, it is connected with wood pieces.

Fig: Steel shutter,steel props,hooked rod

For floor slab, shuttering for slab and beam is combinedly formed. To fit the shuttering of bottom

of the beam timber is used but at first the level is measured with the water level. Dasha is used to

support the bottom shutter of the beam which is fitted on the column and on the center steel

props are used to support it. Beam’s side shutter is fitted, keeping the thickness of slab accurate.

It is made leak proof.

Fig: Beam bottom,side,supported bamboo Fig: Runner,steel props,plywood

Then, for the slab shuttering, pieces of timber is used which is jointed from on end of the slab to

the other end It is known as runner. On it steel grill and plain sheet are placed to complete the

formwork of the slab. Instead of steel grill and plain sheet , plywood is also can be used. The

whole shuttering should be leak proof. In case of steel shutter, glue can be used to fill the pores.

The whole shuttering is supported on the steel props or bamboo. These should be placed

verticallly. In case of bamboo its dia should be 3 inches and matured one is used. Incase of 1st

floor, the sand is being compacted a piece of timber is placed under each bamboo. Commonly,

the gap between props is maintained 2 - 2.5 feet. If we use the pieco beam under the steel shutter

as a support then for a long span, we can reduce the quantity of steel props, which is placed

keeping 3 meter gaps from one another.

Again as previous, the level is measured of the slab and beam shutter with the water level. If the

level is not maintained, then with the level instrument it is levelled accurately.

After the shuttering, the formwork should be cleaned of all rubbish particularly the sawdust

shaving and chippings etc. The surface should be wetted with water as the concrete should come

to well contact.

Removing the formwork is also an important part of formwork.It should be done in the

following order of sequence-

Shuttering forming vertical faces of walls, beams, and columns sides should be

removed first.

Shuttering forming soffit to beams, girders or other heavily loaded member

should be removed in the end.

DURATION TAKEN FOR REMOVAL OF FORMWORK:

1 WALLS COLUMNS & VERTICAL SIDES

OF BEAMS 1-2 DAY

2 SLABS 3 DAYS

3 BEAM SOFFIT 7 DAYS

4 REMOVAL OF PROPS TO SLABS

A) SLAB SPANNINIG UPTO 4.5M 7 DAYS

B) SLAB SPANNINIG OVER 4.5M 14 DAYS

5 REMOVAL OF PROPS TO BEAMS

AND ARCHES

A) SPANNING UPTO 6 MTS 14 DAYS

B) SPANNING OVER 6 MTS 21 DAYS

Limitations:

In practical sites, leak proof is not maintained perfectly.

Sometimes the chamber shapes are deflected from the actual position. Therefore, the

placement sometimes changes of beam or other.

Distance between steel props are not maintained. Therefore, bending of shuttering is

occured .

Conclusion:

The formwork should be made with good quality material and constructed properly. The type of

material to be used for formwork depends upon the nature of construction as well as the

availability and cost of material. In constructing floor slab, we can use plywood as shuttering

instead of timber planks. This type of shuttering ensures quality surface finish that is necessary

for floors.

The material of the formwork should be cheap, easily available and should be suitable for re-use

several times.

Nowadays , steel formwork is widely used in construction as it can be re-used because it is not

easily get damaged. But for the small construction and no need of re-use ,in that type of

construction timber formwork is cheaper than others.

References:

1. 30, East tejturi bazar

Tejgaon,Dhaka.

2. A construction site of a hospital

opposite to AUST

Love road,Dhaka.