Form Work

Formwork:

The term given to the whole setup of temporary moulds into which concrete is poured. Along with

formwork, a system is provided to support the moulds and the concrete till the concrete is set and has

gained enough strength this is known as the Staging. It is also the term given to either temporary or

permanent moulds into which concrete or similar materials are poured. The formwork constitutes 30% of

the project cost and 60% of the project construction time. A temporary framework is used to support the

walkway platform, the access ways and that supports the labours who are laying the skin and placing the

reinforcement is know as Scaffolding. The material which is used to form the mould into which the

concrete is pored is called as Skin. The skin can be made up of ply, steel or aluminium. The process of

placing the skin is known as the Shuttering.

Requirements of a good formwork system:

The essential requirements of formwork or shuttering are:

The material for form should be cheap and it should be suitable for reuse for several times/

It should be practically waterproof so that it does not absorb water from concrete. Also its

shrinkage and swelling should be minimum.

It should be as light as possible.

It should be strong enough to take the dead and live loads during the construction

The joints in the formwork should be rigid so that the bulging, twisting or sagging due to dead

and live load is as small as possible. Excessive deformation may disfigure the surface of concrete

The construction lines in the formwork should be true and the surface plane so that the cost of the

finishing the surface of concrete on removal of shuttering is least.

A formwork should be such that it can be easily erected.

A formwork should be easily removable without any damages to itself so that it can be repeatedly

used.

Factors to be considered for selection of system:

The number of repeat uses

The desired finish

The amount of labour to install each use

Availability of experienced personnels to install it

Handling equipment available to move large sections around

The amount of wet concrete deliverable per cast

The amount of capital available

The speed of project

Versatility

Pour to strip times

The acceptability of cold joints

Materials

The various materials used as forms are:

Timber: It is the most common material for shuttering and is almost available everywhere. It is

comparatively cheaper and could be easily shaped. Timber deteriorates under the stress of heat

and contact with water. It is also difficult to evaluate the proper strength of timber. Thus, a

scientific approach of design becomes difficult.

Plywood: It has got a better surface and gives a smoother finish. These are useful and economical

for larger panels with repetitive uses. Plywood is available is different varieties such as resin ,

plastic coated plywood, texturised surfaces for exposed concrete surface.

Hardwood: they are manufactured from wood fibre under controlled combination of pressure,

heat and moisture. These are tempered with the impregnation of drying oils which are stabilized

by heating. They have improved strength, low water absorption, and better abrasion resistance

and are used as formwork lining.

Fibre forms: They are used as lost forms for concrete. They are left in place on the exposed face

of the concrete where it gives architectural look and also improves acoustical and insulation

properties

Gypsum boards: They are generally used to provide artistic design or ornamental pattern for the

exposed concrete face. It is reinforced with an organic fibre or coir to make it tougher. Concrete

quality may improve due to absorption of extra water present in concrete by these boards.

Plastic forms: PVC, neoprene and polyester strengthened with glass fibre are some of the plastic

forms in use. They are manufactured as per required shapes, do not rust and are easy to clean.

Lost forms: Forms, which are not removed after casting, form a part and parcel of the structure

that behaves as composites. These are known as lost forms or permanent formwork.

Steel form: Steel forms consists of angles, tubes, joists, flat plates, are very much in use as shores,

bracings, runners, slabs, shutters etc. Steel forms are also in use in combination with timber.

These are very strong and can be used repetitively without much damage done to these forms.

The design calculations can be easily done since the characteristics of steel are known.

The advantages and disadvantages of the various forms are listed below.

Untreated wood

o Advantages

Low initial cost

Low experience cost

Low weight

Versatility usually contains sugars that acts as a retardant and prevents sticking

o Disadvantages

Poor finish, patching almost demanded where the finished concrete will be seen

Low per unit use (4-7)

High labour as each set must be rebuilt

Must wait until concrete is well set (24 hours) to strip

Leaves a dusty finish as there are sugars in the sap of soft wood

Untreated Plywood

o Advantages

Same as above but gives a smooth finish

o Disadvantages

Same as above but greater cost and less availability in some countries

Coated Plywood

Densified shuttering:

It is manufactured from selected veneers peeled from hardwood plantation and treated

with specially manufactured phenolic resin for longer durability and better performance. The

surface of shuttering ply is overlaid with 10GSM phenol impregnated film. The sides are

resealed by acrylic paint to preserve moisture absorption and swelling

o Advantages

Will increase durability

Many plywood systems are available:

Oil saturated paper

Vinyl and water resistant glue surface

Simple oil based paint

Increases the number of uses by double as long as edges are not exposed to the

setting of cement

Epoxy paint coatings will extend the use of plywood to over 100 uses

o Disadvantages

Increase initial cost

Increase weight

Release agents is a must

If uncoated surfaces are exposed, the number of uses will be the same as

untreated plywood

More work to clean before each use

Steel form

o Advantages

Has very high reuse rates

Very smooth surfaces are possible

Strong and can be stripped late

Fast to install in simple walls and like

o Disadvantages

Costs are 6-10 times ply

Thicker the surface greater the weight

Steel dents easily

Low versatility

Release agents are demanded

Aluminium Form

o Advantages

Not as easy to damage as steel

Assembles fast

o Disadvantages

Can be very costly to buy

Glass Reinforced Plastic formwork

o Advantages

Very useful for complex shape and special features

Easy to disassemble

Light (not heavy)

Damages on the formwork can be easily be repaired

o Disadvantages

Expensive at first

Classification of formwork

According to size: There are two sizes of formwork – small sized and large sized. Any

size which is designed for operations by workers manually is small sized Timber and

aluminium forms are usually in the form of small sized panels. In case of large sized

formwork, the size of formwork can be designed as large as practicable to reduce the

amount of jointing and to minimize the amount of lift. The stiffness required for the same

can be dealt with the introduction of more stiffeners such as studs and soldiers

According to material: Materials used are traditionally quite limited due to finding the

difficult balance between cost and performance. Timber in general is still the most

popular formwork material for its relatively low initial cost and adaptability. Steel and

aluminium forms are becoming more commonly used now-a-days because of their higher

number of repetitions but the cost and labour requirements is high for the same.

Design criteria:

For Slab

o Thickness

o Load calculation

o Pouring method

o Type of form

o Spacing of props/ vertical shore

o Capacity of spanning member

o Floor Height

For walls/columns

o Rate of rise

o Temperature at site

o Pressure diagram

o Material selection

o Height of form

o Handling facilities of forms

o Selection of forms

o Section of columns and wall

Formwork design loads:

1. Vertical loads:

a) Weight of wet concrete

b) Self weight

c) Live load during construction

d) Uplift due to uneven placing of concrete

2. Lateral loads

a. Density

b. Rate of placing

c. Vibration

d. Concrete temperature

e. Slump

f. Admixture

g. Thickness of concrete element

3. Horizontal loads

a. Mainly on alignment/ supporting props

b. Due to wind

c. Due to dumping of concrete

d. Due to equipment

Types of formwork systems

1. Al- Titan system

The skin is backed up by aluminium secondary beams (1.7m, 2.3m, 3.3m length) also known as

aluminium doka. These beams have strip of wood running along their length on the top to

facilitate fixing the plywood with nails. This fits into the groove of primary beam and forms a

decking to enable the placing of plywood and also replaces the 4”x3” runner which is generally

used as beam bottom. The aluminium secondary beam (2.3m or 3.3m) is used in wall or column

shuttering. The holes are provided to fix the steel walers which generally take care of concrete

pressure. Aluminium primary usually 1.2m or 1.8m long is used to support the slab along with

secondary beam. The groove on either side receives the secondary beam. The end collars will

sit in the fly plate of drop head. The drop heads are supported by the staging.

The main advantages are:

The component are light weight hence easy to handle

The drop heads facilitate in achieving faster cycle time as the skin and the beams can be

removed soon with only supporting system in place.

Deshuttering is easy

Large number of repetitions can be obtained.

Primarybeam

Secondary beam

Drop head

2. L&T Doka System

The skin is stiffened by timber beams (I- sections). These are designated as H16 (160mm deep)

as secondary beams and H20 (200mm deep) as primary beams. The skin is nailed to the flanges

of secondary timber beams which rest on primary timber beam. These primary beams are

supported over four way heads which are attached to a supporting system. For vertical

members, the beams used are of H16.

Primary beam four way head

3. Conventional system

It is the commonly used system mainly because of its ease and availability of the components.

The skin is stiffened by wooden runners of dimensions 2”x3” or 3”x4”. In some cases LVR’s

are also used. These stiffeners rest on wooden rubber wood, placed 300 to350mm c/c, or

LVR’s, placed 400mm c/c, this in turn rests on ISMC channels placed on stirrups heads that is

supported by the scaffolding system.

Types of scaffolding systems:

a. Cuplock system

This system takes both vertical and inclined loads. Its components are:

Cuplock verticals: made from 40NB tubes. The bottom cups are welded every .5m and the top

cups are movable. They are available in sizes .5m, 1m, 1.5m, 2m, 2.5m and 3m. the maximum

safe loading capacity is 2T when the horizontals are placed at 2m spacing

Cuplock horizontals: made from 40NB tubes with blades welded at ends. These are used to

make cuplock staging grids. These are also called as bracings. These are spaced as per design

requirements along with cuplock vertical. The various sizes are 2.5m, 2m, 1.8m, 1.5m, 1.2m,

1m and .86m.

Spigot: when the room height is great, a need for using one cuplock vertical on top of another is

required. In such a case a spigot is used. These have holes on either side to accommodate the

spigot pin. At site instead of spigot pins, 8mm diameter bolts is used. These spigots have

diameter less than that of cuplock vertical.

Base jack: They are used at the bottom of verticals. A screw jack arrangement is used to adjust

the height. They are threaded to a length of 600mm out of which 500mm can be safely

extruded. Its safe load carrying capacity is 6T

Stirrup heads: They are used at the top of verticals. It also has screw jack arrangement to adjust

the height. They are threaded to a length of 650mm out of which 500mm can be safely

extruded.

b. Flex systems

This system is ideally suited for different types of floors with varying thickness and shapes. It is

simple and quick to use. This system mainly consists of floor props and tripods. They can be used for

beam and slab formwork, shoring, aligning formwork for walls and columns. The tripod provided

which vertical support is given ensures stability against inclined loads. The props are telescopic and

adjustments can be made in height. The lightweight H-16 beams and the four way heads combine to

give a versatile formwork system.

The four way heads hold the light weight beams whether they are kept continuously joined or

overlapping. This can be adopted for varying room dimensions without the need to cut the H-16

beams. Such beams can be supported at any point along the length, with no restriction of spacing.

Hence it can be easily adopted for varying floor thickness and changing room dimensions.

Arrangement of doka flex system

12 MM PLY

AS

SHEATHING

H-16 BEAMS

(PRIMARY)

H-16 BEAMS (SEC)

CT PROPS

H-16

BEAMS

(PRIMARY

)

TRIPOD

BEAM FORMING HEAD

FOURWAY

HEAD

c. HD tower systems

It is ideal in places where the scaffold has to carry heavy loads or the scaffold height required is

high. The vertical members are made from 50NB medium class pipes and horizontal members are

made out of 40NB pipes. The horizontal members are welded into vertical members thus forming

the basic frame. The safe load carrying capacity is 6T per leg. A foot plate is provided at the

bottom to transmit the load uniformly to the ground from the HD tower. A U-head is provided at

the top to receive and transmit the load to HD tower.

Arrangement of Doka HDT system

MISC Components:

Steel walers: it is made up of two ISMC 100 laid back to back with a spacer plate. It is fixed

around the periphery of columns, walls or beam sides to withstand the concrete pressure and

prevent bulging of concrete. They are available in .8m, 1.2m, 1.6m, 2m and 2.4m lengths. At

site, cuplock horizontals tied together with binding wire is also being used.

H.D.TOWER

SYSTEM

SHORT PROPS

STEEL WALER

H-16 BEAMS

TOWER SPINDLE

U-HEAD

FOOT PLATE

Steel waler

Tie rods and wing nuts: They are steel rods which are threaded so that nuts called wing nuts can

be attached to them. They are used to fix the steel walers around the columns, walls or beam

sides. In case of beams and walls, PVC pipes are placed through the section at required

intervals and the tie rod passes through these PVC pipes. The tie rod also passes through the

space created by the spacer plates in the walers. The wing nut is then fixed and tightened to

secure them. When concrete is poured into moulds, the tie rods come into tension. The

maximum allowable tension force is 50kN.

Mild Steel panels: They are used in place of plywood as skin. They are of two types: wall form

panels and floor form panels. These panels are stiffened by a steel strip which has grooves in it.

A single clip or a double clip can be fixed into these groves to attach a pipe along the length.

This is done to ensure that the panels are in line.

Coupler: they are used to connect two pipes together. They can be either right angle coupler or

swivel type coupler, where the angle between the two pipes can be changed.

Mivan system:

It is the most advanced formwork systems. It is fast, simple and adaptable. It produces total

quality work which requires minimum maintenance and when durability is the prime consideration. It

is a totally pre-engineered system where in the complete methodology is planned to the finest details.

In this system the walls, columns and slab are casted in one continuous pour on concrete. Early

removal of forms can be achieved by the air curing/ curing compounds. These forms are made strong

and sturdy, fabricated with accuracy and easy to handle. The components are made out of aluminium

and hence are very light weight. They afford large number of repetitions (around 250). The re-

propping is simple hence short cycle time can be achieved.

Construction with Mivan

A) PRE – CONCRETE ACTIVITIES

a) Receipt of Equipment on Site – The equipments is received in the site as ordered.

b) Level Surveys – Level checking are made to maintain horizontal level check.

c) Setting Out – The setting out of the formwork is done.

d) Control / Correction of Deviation – Deviation or any correction are carried out.

e) Erect Formwork – The formwork is erected on site.

f) Erect Deck Formwork – Deck is erected for labours to work.

g) Setting Kickers – kickers are provided over the beam.

After the above activities have been completed it is necessary to check the following.

1. All formwork should be cleaned and coated with approved realize agent.

2. Ensure wall formwork is erected to the setting out lines.

3. Check all openings are of correct dimensions, not twist.

4. Check all horizontal formwork (deck soffit, and beam soffit etc.) in level.

5. Ensure deck and beam props are vertical and there is vertical movement in the prop lengths.

6. Check wall ties, pins and wedges are all in position and secure.

7. Any surplus material or items to be cleared from the area to be cast.

8. Ensure working platform brackets are securely fastened to the concrete.

B) ON CONCRETE ACTIVITIES

At least two operatives should be on stand by during concreting for checking pins, wedges and wall

ties as the pour is in progress. Pins, wedges or wall ties missing could lead to a movement of the

formwork and possibility of the formwork being damaged. This – effected area will then required

remedial work after striking of the formwork.

Things to look for during concreting:

i. Dislodging of pins / wedges due to vibration.

ii. Beam / deck props adjacent to drop areas slipping due to vibration.

iii. Ensure all bracing at special areas slipping due to vibration.

iv. Overspill of concrete at window opening etc.

C) POST – CONCRETE ACTIVITIES

i) Strike Wall Form- It is required to strike down the wall form.

ii) Strike Deck Form- The deck form is then removed.

iii) Clean, Transport and stack formwork

iv) Strike kicker Formwork – The kicker are removed.

v) Strike wall – Mounted on a Working Platform the wall are fitted on next floor.

vi) Erect Wall – Mount Working Platform and the wall is erected.

Normally all formwork can be struck after 12 hours.

The post-concreting activities include:

CLEANING

All components should be cleaned with scrapers and wire brushes as soon as they are struck. Wire

brush is to be used on side rails only. The longer cleaning is delayed, the more difficult the task will

be. It is usually best to clean panels in the area where they are struck.

TRANSPORTING

There are basic three methods recommended when transporting to the next floor:

The heaviest and the longest, which is a full height of wall panel, can be carried up the

nearest stairway.

Passes through void areas.

Rose through slots specially formed in the floor slab for this purpose. Once they have

served their purpose they are closed by casting in concrete filter.

STRIKING

Once cleaned and transported to the next point of erection, panels should be stacked at right

place and in right order. Proper stacking is a clean sign of a wall – managed operation greatly aids

the next sequence of erection as well as prevents clutters and impend other activities

Components of formwork

The basic element of the formwork is the panel, which is an extruded aluminium rail section, welded to an

aluminium sheet. This produces a lightweight panel with an excellent stiffness to weight ratio, yielding

minimal deflection under concrete loading. Panels are manufactured in the size and shape to suit the

requirements of specific projects.

The panels are made from high strength aluminium alloy with a 4 mm thick skin plate and 6mm

thick ribbing behind to stiffen the panels. The panels are manufactured in MIVAN’S dedicated factories

in Europe and South East Asia. Once they are assembled they are subjected to a trial erection in order to

eliminate any dimensional or on site problems.

All the formwork components are received at the site whining three months after they are ordered.

Following are the components that are regularly used in the construction.

Beam components

1) Beam Side Panel: - It forms the side of the beams. It is a rectangular structure and is cut according to

the size of the beam

BEAM SIDE PANEL

2) Prop Head for Soffit Beam: - It forms the soffit beam. It is a V-shaped head for easy dislodging of the

formwork.

PROP HEAD FOR SOFFIT BEAM.

3) Beam Soffit Panel: - It supports the soffit beam. It is a plain rectangular structure of aluminium.

BEAM SOFFIT-PANEL

4) Beam Soffit Bulkhead: - It is the bulkhead for beam. It carries most of the bulk load.

BEAM SOFFIT BULKHEAD

Deck Components

1) Deck Panel: - It forms the horizontal surface for casting of slabs. It is built for proper safety of

workers.

DECK PANEL

2) Deck Prop: - It forms a V-shaped prop head. It supports the deck and bears the load coming on the

deck panel.

DECK PROP

3) Prop Length: - It is the length of the prop. It depends upon the length of the slab.

DECK PROP LENGTH

4) Deck mid – Beam: - It supports the middle portion of the beam. It holds the concrete.

DECK MID-BEAM

5) Soffit Length: - It provides support to the edge of the deck panels at their perimeter of the room.

SOFFIT LENGTH

6) Deck Beam Bar: - It is the deck for the beam. This component supports the deck and beam.

DECK BEAM BAR

Other Components

1) Internal Soffit Corner: - It forms the vertical internal corner between the walls and the beams,

slabs, and the horizontal internal cornice between the walls and the beam slabs and the beam soffit.

INTERNAL SOFFIT CORNER

2) External Soffit Corner: - It forms the external corner between the components

EXTERNAL SOFFIT CORNER

3) External Corner: - It forms the external corner of the formwork system.

EXTENAL CORNER

4) Internal Corner: - It connects two pieces of vertical formwork pieces at their exterior intersections.

INTERNAL CORNERS

Wall Components

a) Wall Panel: - It forms the face of the wall. It is an Aluminium sheet properly cut to fit the exact size

of the wall

WALL PANEL

b) Rocker: - It is a supporting component of wall. It is L-shaped panel having allotment holes for stub

pin.

ROCKER

c) Kicker: - It forms the wall face at the top of the panels and acts as a ledge to support

KICKER

d) Stub Pin: - It helps in joining two wall panels. It helps in joining two joints

STUB PIN

Work cycle

MIVAN is a system for scheduling & controlling the work of other connected construction trades

such as steel reinforcement, concrete placements & electrical inserts. The work at site hence follows a

particular sequence. The work cycle begins with the deshuttering of the panels. It takes about 12-15hrs. It

is followed by positioning of the brackets & platforms on the level. It takes about 10-15hrs

simultaneously.

The deshuttered panels are lifted & fixed on the floor .The activity requires 7-10 hours. Kicker &

External shutters are fixed in 7 hrs. The wall shutters are erected in 6-8 hrs One of the major activity

reinforcement requires 10-12 hrs. The fixing of the electrical conduits takes about 10 hrs and finally

pouring of concrete takes place in these.

This is a well synchronized work cycle for a period of 7 days. A period of 10-12 hrs is left after

concreting for the concrete to gain strength before the beginning of the next cycle. This work schedule has

been planned for 1010-1080 sq m of formwork with 72-25cu m of concreting & approximate

reinforcement.

The formwork assembling at the site is a quick & easy process. On leaving the MIVAN factory all

panels are clearly labeled to ensure that they are easily identifiable on site and can be smoothly fitted

together using formwork modulation drawings. All formwork begins from corners and proceeds from

there.

The system usually follows a four day cycle: -

Day 1: -The first activity consists of erection of vertical reinforcement bars and one side of the vertical

formwork for the entire floor or a part of one floor.

Day 2: -The second activity involves erection of the second side of the vertical formwork and formwork

for the floor

Day 3: - Fixing reinforcement bars for floor slabs and casting of walls and slabs.

Day 4: -Removal of vertical form work panels after 24hours, leaving the props in place for 7 days and

floor slab formwork in place for 2.5 days.

Advantages of mivan:

High quality formwork ensures consistence of dimensions

On removal of mould a high quality concrete finish is produced to accurate tolerances and

verticality

Total system forms the complete concrete structures

Custom designed to suit project requirements

Unsurpassed construction speed

Panels can be reused up to 250 times

Can be erected using unskilled labour

Limitations of mivan:

Because of small sizes finishing lines are seen on the concrete surfaces.

Concealed services become difficult due to small thickness of components.

It requires uniform planning as well as uniform elevations to be cost effective.

Modifications are not possible as all members are caste in RCC.

Large volume of work is necessary to be cost effective i.e. at least 200 repetitions of the forms

should be possible at work.

The formwork requires number of spacer, wall ties etc. which are placed @ 2 feet c/c; these

create problems such as seepage, leakages during monsoon.

Due to box-type construction shrinkage cracks are likely to appear.

Heat of Hydration is high due to shear walls.

Remedial measures

Ties used in shutter connection should be carefully grouted.

Shrinkage cracks likely to occur around door and window openings in the wall can be minimized

by providing control strips in the structure which could be concreted after a delay of about 3 to 7

days after major concreting

Heat of hydration can be reduced by the use of fly ash.

Conventional Vs Mivan

Advantages of Mivan formwork over conventional construction

1. More seismic resistance: - The box type construction provides more seismic resistance to the

structure.

2. Increased durability: - The durability of a complete concrete structure is more than conventional brick

bat masonry.

3. Lesser number of joints thereby reducing the leakages and enhancing the durability.

4. Higher carpet area- Due to shear walls the walls are thin thus increasing area.

5. Integral and smooth finishing of wall and slab- Smooth finish of aluminium can be seen vividly on

walls.

6. Uniform quality of construction – Uniform grade of concrete is used.

7. Negligible maintenance – Strong built up of concrete needs no maintenance.

8. Faster completion – Unsurpassed construction speed can be achieved due to light weight of forms

9. Lesser manual labour- Less labour is required for carrying formworks.

10. Simplified foundation design due to consistent load distribution.

11. The natural density of concrete wall result in better sound transmission coefficient.

Special types of formwork:

Climbing Platform for Lift Shafts

This is a system developed particularly for constructing lift shafts (Lift Core wall), this system eliminates

the need for providing scaffolding up to the working stage from the floor, and hence it is most suitable for

high rise construction. This consists of a platform with climbing pawls attached at each corner. These

pawls are made to fit and rest in pockets left out during the concreting of the wall. Once the next stage is

ready, this platform can be pulled up by a crane, during which the pawls drop down due to their own

weight and roll up to the next pocket. Once the pocket of the next stage is reached, the crane releases the

platform and the pawls fit into the pockets, hence providing a working platform for the next stage.

Types

Climbing formwork (crane-climbing) - in this type of climbing formwork, the formwork around

the structure is displaced upwards with the help of one or more cranes once the hardening of the

concrete has proceeded far enough. This may entail lifting the whole section, or be achieved

segmentally.

Climbing formwork (self-climbing) - In this type of formwork, the structure elevates itself with

the help of mechanic leverage equipment (usually hydraulic). To do this, it fixes itself to

sacrificial cones or rails emplaced in the previously cast concrete.

Lift shaft platform resting in pockets Lift shaft platform being lifted to next level

Jump forms

These are forms that are able to be moved in leaps either horizontally or vertically. They are simple

reusable panels which can be fixed to a previous rise of wall. They may be used when identical units are

being constructed. The panels must be stronger than single use panels for the same section of concrete

because they must withstand movement. The extra costs of building stronger panels are recovered when

they are re-used. The total building time is less and the overall use of material is less.

Slip forms

A slip form is made so that it can move slowly whilst being continually kept full of concrete. The form is

not deep and it moves so that the concrete is not in the form for long time. The concrete is left behind by

the form when it is just strong enough to support itself. Typically, the concrete stays in the vertical slip

form for 1.5 to 6 hours. Because the form is continually filled it produces joint less concrete. That’s useful

for construction of containers, such as water tanks, cooling towers etc. where breaks in concrete should be

avoided.

Pipe racks Core walls

Permanent formwork

Permanent formwork is a structural element that is used to contain the placed concrete, mould it to the

required dimensions and remain in place for the life of the structure. It can be of two types: Participating

permanent formwork or non participating permanent formwork. Participating permanent formwork makes

some predetermined contribution to the strength of the structure. Non-participating permanent formwork

makes no strength contribution but may provide additional benefits such as improved durability, finish or

insulation properties.

The correct use of permanent formwork in construction will reduce costs and save time by:

eliminating or reducing the need for false work

reducing the skill level needed on site

increasing the potential for standardisation and repetition

permitting off-site fabrication in factory conditions followed by scheduled and appropriate

deliveries

speeding up erection times, particularly in building works

eliminating the need to strike formwork and false work

allowing early access for following or concurrent operations

eliminating the programme limitations of re-use of formwork

The correct use of permanent formwork in construction will reduce hazards by:

eliminating or reducing the need to erect formwork and false work in difficult locations, for

example over rail tracks and water, particularly in bridge works

providing a safe working platform early in the erection process

Eliminating the need to strike formwork in difficult locations and confined spaces.

The correct use of permanent formwork in construction will reduce maintenance costs by:

improving curing of concrete and reducing shrinkage cracking

ensuring adequate cover to the reinforcement and providing associated benefits such as increased

resistance to chloride ingress and carbonation, where appropriate

in many instances improving the durability of the structure

providing the decorative finish required

Insulated Concrete Formwork

The ICF consists of twin-walled expanded polystyrene (EPS) panels or blocks that are quickly built up to

create formwork for the walls of a building. This formwork is then filled with factory produced, quality

assured, ready-mixed concrete to create a robust structure. The forms are thermally efficient with the EPS

remaining in place to provide both complete thermal insulation and a uniform surface ready for the direct

application of external finishes or proprietary cladding systems. ICF construction sandwiches a heavy

high strength material between layers of light, highly insulated one (EPS or foam). The combination

creates a wall with many desirable properties such as air tightness, strength, sound attenuation, insulation

and mass. Buildings constructed with ICF walls have a more even temperature throughout the day and

night.

Insulated concrete formwork

The Table or Flying Form System

Another type of formwork is table or flying form systems. These consist of slab formwork tables which

are reusable. These tables do not have to be dismantled and can be used in high buildings where cranes or

elevators are used to lift the tables. Once the table is positioned, the space between the wall and table is

filled. Tables vary in size from eight square meters to 150 square meters. This type of formwork is a huge

saver of both labour and time and is a favourite of construction engineers and architects. However, table

formwork is best used in the construction of large, but simple structures.

Formwork should be placed at the correct height so that there is sufficient space to remove them once the

concrete has set or cured. Due to this reason, the support systems of table formwork need to be height

adjustable. Adjustable metal props can be used to support the systems. Some use steel or aluminium to

insert stringers and supports into the systems, while others use metal frame shoring towers to attach the

decks to. Others attach the decks to walls or columns that have been pre-cast which means that

contractors do not need to use vertical props, simply support shoes bolted through holes.

Table formwork system

Tunnel form system

Tunnel form is a formwork system where slabs & walls of a building is cast in a continuous pour using

room sized structural steel mould. The components of this system are made of steel. The system creates

an efficient load-bearing structure for use in a wide variety of applications. It is particularly effective in

projects suited to repetitive cellular construction such as residential blocks, hotels, student

accommodation, barracks and prisons. The solid, strong monolithic structure can be 40 or more storeys in

height and the accuracy of the system suits the installation of prefabricated elements such as cladding

panels and bathroom pods.

It has been suggested that tunnel form can reduce the cost of the frame of a typical hotel or similar

building by about 15% when compared with traditional construction, chiefly due to the increased speed of

construction. Savings in construction time of up to 25% over traditional frame construction methods can

be achieved; for low-rise construction, which would traditionally be in brick or block, savings of 45% on

the construction time have been achieved

Fabric Formwork

Fabric formwork uses a flexible textile membrane in place of the rigid formwork panels usually

used in concrete construction. Rigid materials such as dimensional lumber, plywood, or aluminum are

conventionally used to restrain the fluid forces of the concrete. In order to restrain these forces, the form

will have tension forces on one surface, compressive forces on the other surface, and a neutral plane

between the two surfaces. Fabric, however, can only operate in tension, and as a result can be an

extremely efficient method of forming concrete. When wet concrete is contained by a tensile membrane,

the fabric deflects into precise tension geometries. This produces efficient structural curves and

extraordinary surface finishes. Fabric weighs approximately 1/300th that of dimensional lumber. But the

pressure that concrete exerts on the fibre results in bulging or deflection of the structure. This means that

fabric can only be used where the bulging is not detrimental to the finished concrete.

Fabric forms can be used to form columns, walls, beams, slabs and panels in both pre-cast and in-situ

construction. From a structural/architectural perspective, fabric formwork awakens concrete to its fluid

origins, introducing new horizons for architectural form and structural expression.

Fabric formwork being placed at site

Advantages of Fabric Forms

Material Reduction: Fabric forms use hundreds of times less material than conventional rigid

formwork. Concrete and steel can also be conserved by forming more efficient curved

geometries.

Cost Savings: Fabric forms cost far less than rigid forms due to the efficiency of the tensile-only

membrane. In addition, certain fabrics can be reused many times over.

Improved Concrete Quality: Permeable fabrics improve surface finish, compression, strength

and impermeability by filtering air bubbles and excess mix water from the wet concrete.

Waterproof Concrete: Inexpensive plastic-coated fabric forms provide a permanent waterproof

shield when left on a concrete cast - useful, for example, in damp-proofing foundation footings.

Beauty: Fabric-cast concrete is distinguished by its soft curves and immaculately detailed

surfaces, offering unique forms of architectural beauty to concrete products and construction.

Formwork Failures

The most common reason due to which failure occurs when concrete is fresh is due to the formwork

failure. The main reasons for which Formwork failure can occur are:

Improper stripping and shore removal

Premature stripping of forms, premature removal of shores, and careless practices in

reshoring can produce catastrophic results.

Inadequate bracing

This is one of the more frequent causes of formwork failure, however, other effects are

that induce lateral force components or induce displacement of supporting members.

Inadequate cross bracing and horizontal bracing of shores is one of the factors most

frequently involved in formwork accidents. High shoring with heavy load at the top is

vulnerable to eccentric or lateral loading. Diagonal bracing improves the stability of a

structure as struts to solid ground.

Vibration

Forms sometimes collapse when their supporting shores or jacks are displaced by

vibration caused by:

* Passing traffic

* Movement of workers and equipment on the formwork

* The effect of vibrating concrete to consolidate it.

Diagonal bracing can help prevent failure due to vibration.

Unstable soil under mudsills

Formwork should be safe if it is adequately braced and constructed so all loads are

carried to solid ground through vertical members. Shores must be set plumb and the

ground must be able to carry the load without settling. Shores and mudsills must not rest

on frozen ground; moisture and heat from the concreting operations, or changing air

temperatures, may thaw the soil and allow settlement that overloads or shifts the

formwork. Site drainage must be adequate to prevent a washout of soil supporting the

mudsills.

Inadequate control of concrete placement

The temperature and rate of vertical placement of concrete are factors influencing the

development of lateral pressures that act on the forms. If temperature drops during

construction operations, rate of concreting often has to be slowed down to prevent a built

up of lateral pressure overloading the forms. If this is not done, formwork failure may

result. Failure to regulate properly the rate and order of placing concrete on horizontal

surfaces or curved roofs may produce unbalanced loadings and consequent failures of

formwork.

Lack of attention to formwork details

Even when the basic formwork design is soundly conceived, small differences in

assembly details may cause local weakness or overstress loading to form failure. This

may be as simple as insufficient nailing, or failure to tighten the locking devices on metal

shoring.

Placing of formwork

At site, the cuplock system with wooden runners is being used.

Columns: First the construction of the kicker is done. The ply of dimension is 1.2mx2.4m is cut

into the required shape. This is stiffened with the help of wooden runners placed at 200-

300mmc/c. a thin coat of shuttering oil is applied on the surface which acts as the release agent.

With reference to column starter these boards are put into place and nailed. Props are provided to

support them; these props rest on rigid surface and are used to either pull or push the boards. The

inner dimensions of the formwork are checked. Line dori suspended alongside the boards is used

to check its plumb. Distances of the line dori from the surface of the ply measured at salient

points and adjustments are made using the props.

Footing: After the reinforcement is tied, the cover blocks are placed and the ply is placed. These

ply boards are held in position with the help of props. The verticality is checked with the help of

plumb and also the inner dimensions are checked. The level of concrete is marked on the ply

using a nail.

Beams and slabs: A detailed plan of scaffolding layout is made, based on the shuttering layout

drawing, and the scaffolding is erected accordingly. The scaffolding is approximately drawn up to

the required level. The ISMC channels, which act as the primary beams are put in the stirrup

heads and on top of it wooden runners or rubber wood whichever is used is placed. The beam

bottom skin is then nailed to these runners which act as secondary beams. Beam side skin is then

nailed and fixed. The slab bottom is fixed after this. All this is done with reference to the column

alignment. The dimensions of beams are checked and all required rectifications done. The

corrections are made by adjusting the scaffolding heights.

Cycle time

Cycle time is the time period for which the formwork is utilized for a particular stage. It starts from the

time the material is made available for that particular stage, includes the time for erection, time for which

it remains in place and the time taken for de-shuttering. After deshuttering the material can be utilized for

the next stage

De-shuttering time

It is the time for which the form work remains in place after the concrete has been poured. This depends

on several factors like the type of member (Slab, Beam bottom, beam sides, column, etc…).

Span of the member (in case of beams and slabs).

Depth of the member.

Type of formwork used (If there is a provision for Props being left under, the Deshuttering time

can be improved).

Use of admixtures in concrete. Etc…

At site:

Description Deshuttering time

Wall, column and vertical beam sides 24-48hrs

Slabs ( props left under) 3 days

Beam soffits (props left under) 7 days

Removal of props to slab

Spanning up to 4.5m 7 days

Spanning greater than 4.5m 14 days

Removal of props to beams and arches

Spanning up to 6m 14 days

Spanning greater than 6m 21 days

Usage ratio

This is the ratio of the total area of shuttering done (measured in m2) and the total amount of shuttering

material available on site (measured in m2), in a given time period. This value gives an idea about the

utility of the material. Higher the value greater is the utility.

Economy in formwork

The following steps or measures can be taken to reduce the cost of formwork and hence achieve

economy:

The use of irregular shapes for forms should be avoided as far as possible.

The structural components should be so designed as to permit the use of commercially available

forms.

The working drawings of the formwork should be prepared and checked before fabricating it.

The forms should be designed to provide adequate but not excessive strength and rigidity.

The use of construction joints should be made to improve the quality of forms and to make re-use

of forms

Misc learnings:

Staging should be placed such that it should be at a distance of 300mm from column face. If the

distance becomes more, then extra supports should be provided

When ply is being cut for beam side, the width is equal to beam depth- slab depth + runner width

1 lt of shuttering oil can cover 35sqft of film coated plywood

One board of ply requires about 40g of nails to prepare shuttering for column, beam and slab

For the UG tank, the water stop tie rods are to be used thereby preventing leakage. After the

concreting.

For pile caps, about 120gms nails is required for making and fixing.

For circular column, steel form with angle sections is used to make the work easier compared to

the usage of wooden form

Good practices:

The formwork after being used should be cleaned properly and stacked separately for easy use.

Adequate release agents should be applied to the board such that it can be easy deshutterd but

care should be taken that concrete won’t get stained

The shuttering ply should be planned and cut in such a way that minimum wastages occur.

The shuttering usage ratio should be kept high thereby increasing the utility of the ply

The column box shuttering can be reused for beam bottom after 12-15 repetitions.

The amount of staging procured can be more than the amount of ply procured. There by the

staging can be laid before providing greater work front also the placing of ply becomes easier.

Exercising proper care and maintenance of the shuttering material increases their durability and

more number of repetitions; thereby making the investment worthy.