FORMWORK FORMWORK
FORMWORKFORMWORKFORMWORKFORMWORK
FormworkFormworkConcrete being plastic material in fresh state, is kept in a
moulds till it gain reasonable strength, this temporary
structure is called “Formwork”.
It is closed from all sides and can carry the hydrostatic load
of fluid concrete, additional load due to vibration, and load
of men and machinery.of men and machinery.
Formwork should be such that it can be easily removed after
hardening of concrete.
Timber, plywood panels or steel sheets are used for
formwork. The initial cost of steel forms may be high but
they can be repeatedly used for a number of times.
ShutteringShutteringShuttering is a temporary platform constructed with the help
of wooden planks, wooden logs, steel rods or bamboos over
which formwork is supported and ultimately pouring of
concrete is done.
scaffoldingscaffoldingScaffolding is a grid of bamboos, wooden planks or circular
steel pipes by which labour can have access to any point of
the structure to be constructed and further formwork and
shuttering can rest over it .
Steel scaffolding is most commonly used as it is easy to
dismantle and reassemble.dismantle and reassemble.
ShoringShoringShoring is the temporary support given to the existing
structure for repair purposes. When dismantling any central
building, the surrounding building is also temporarily
supported.
Basic Requirements of a Good Formwork
Basic Requirements of a Good Formwork
Formwork must be strong enough.
Formwork should be smooth to get a smooth surface
of the required member.
Formwork should be true.Formwork should be true.
Formwork should be such that it can easily be
removed without damaging the surface.
Deflections is the most important considerations.
Formwork must be water tight.
Formwork should be as economical as possible.
Formwork CostFormwork CostCost of Formwork for RCC
Concrete 35%
Reinforcement 35%
Formwork 30%
The exact proportions of cost are, however, affected be the
following factors:
(i). The simplicity or complexity of the structure.
(ii). The availability of the repeated formwork.
(iii). The specified surface appearance of the concrete.
Formwork CostFormwork CostCost of Formwork for Building Structures
Formwork cost is a major part of the total cost and normally
varies from 30% to 65% for building works; however, for
complicated works or with special surface finishes such as
helical stair cases or for the construction of minars, it mayhelical stair cases or for the construction of minars, it may
increase up to as much as 80%.
Formwork CostFormwork CostCost of Formwork for Huge C.E. Works
The cost of formwork varies from 5% to 25% of the total
cost for bridges, highway, and dam construction, etc.
Such jobs are bigger in magnitude and again lot of money isSuch jobs are bigger in magnitude and again lot of money is
required for formwork necessitating careful design.
Wooden Formwork for R.C.C. Walls
Wooden Formwork for R.C.C. Walls
It includes sheathing, studs, wales, ties and braces.
Sheathing is the layer which constitutes the inner surface of
the form and is immediately in contact with the concrete.
If solid timber is used for sheathing, it may be 1", 11/4", 11/2",
2" thick, the opposite sides of the wall form are held in
correct positions by steel form ties, which resist the lateral
pressure of the concrete and serve as spacers to govern
width of the space between the forms.
Wooden Formwork for R.C.C. Walls
Wooden Formwork for R.C.C. Walls
The form ties usually have a safe working strength of 3000
lbs.
Sheathing is supported by closely spaced vertical timber
studs which are further supported by the horizontal wales.
The sizes of studs and wales may be 2" x 4", 2" x 6", 3" x 4",The sizes of studs and wales may be 2" x 4", 2" x 6", 3" x 4",
3" x 6" and 4" x 4", etc.
Steel ties are fixed with the help of ties clamps to the wales
and these are cut to remove the formwork when concrete is
hardened.
The form, as a whole, is stabilized by inclined braces
consisting of wooden battens or bamboos etc. Braces are
held rigidly in position by cleats on the form and by properly
driven stacks at the ground.
9’6
”
Wall
tie3/4” plywood sheathing2”x 4”x 10’- 0 “ stud2- 2”x 4”
wale
2”x 4” x 10’- 0”
brace @ 6’- 0”
Concrete Footing
9’6
”
2”x 4” sill
25’4”
Side ElevationSection through the Wall
2”x 4”x 3’- 0”
Stake @ 6’- 0”
Pressure on the FormworkPressure on the Formwork
Maximum pressure of fresh concrete on the formwork ismainly influenced by the following factors.
1) Rate of pouring of concrete which is generally 4 to 5 ft perhour.
2) Temperature of concrete. If temperature is lower, the2) Temperature of concrete. If temperature is lower, theconcrete will remain in fluid form for longer time.
3) Workability of concrete. Workable concrete will have morefluidity and hence will exert more pressure.
4) Thickness of concrete wall. Pressure will be lower in thinwalls because of the arching action in the cross-section.
5) Vibration of concrete.
Floor Slab Formwork or Deck
Formwork
Floor Slab Formwork or Deck
Formwork
Following points are important for deck formwork.
1) It should be properly designed to withstand the imposedloads.
2) Loads are taken directly by plywood/ steel/solid timbersoffit sheathing. The sheathing and joists (secondarysoffit sheathing. The sheathing and joists (secondarybeams) must be water tight to prevent any leakage orgrout.
3) Normally the size of panels used for sheathing is 8 x 4 in.and these are placed side by side.
4) Plywood sheathing, if used, is normally thick otherwisethick commercial wooden planks may be used for the deckformwork.
Floor Slab Formwork or Deck
Formwork
Floor Slab Formwork or Deck
Formwork
5. Soffit sheathing is supported by timber-joists (secondarybeams), which are further supported by more widelyspaced joists (main beams) at right angles to the secondarybeams. Main beams transfer load to adjustable metal propsand then the load is carried to the foundation.
6. It may be designed for a particular surface-finish ifrequired.
7. Double system of joists allows the vertical props to bespaced at reasonable distance in-between to carry full loadbut, at the same time, to permit the movement of men andmachinery in-between.
8. Lateral and diagonal bracing of props may be provided forstability, which prevent side sway.
Formwork for Beam & Slab
Floor
Formwork for Beam & Slab
Floor
Formwork for ColumnsFormwork for Columns
This type of form-work consists of two end and two sideplanks built in one unit or panel.
The height of each panel is built equal to the storey heightless slab thickness and the floor sheeting.
The two end planks are built in width equal to theThe two end planks are built in width equal to thedimensions of the column plus twice thickness of thesheeting. The width of the sheeting will be same as thedimension of the column.
The yokes will project 20 to 25 cm beyond the sheeting ateach end as shown in fig. The spacing of the yokes will besame on both the sides. Bolt holes are created in the sideyokes, about 3 mm larger than the size of the bolt, forpassing and tightening the bolts easily.
Formwork failuresFormwork failuresGenerally some unexpected event causes one member to fail,
then others become overloaded or misaligned and the entire
formwork structure collapses.
Raft foundation formworkRaft foundation formwork
Raft foundation formworkRaft foundation formwork
TYPESTYPESTYPESTYPES OFOFOFOF CIVILCIVILCIVILCIVIL ENGINEERINGENGINEERINGENGINEERINGENGINEERING CONTRACTSCONTRACTSCONTRACTSCONTRACTS
Some of the commonly used types are explained
below:
1- Bill of Quantities Contract.
� This type of contract which includes a BOQ (bill� This type of contract which includes a BOQ (bill
of quantities) priced by the contractor is the most
commonly used form of contract for civil
engineering works.
� This type of contract is also known as “Item
rate contract”. Bill of quantities greatly assists in
keeping the tender cost as low as possible because
there is maximum competition among the
contractors.40
2- Scheduled Contract
In this type of contract the client refers to aschedule of unit rates covering each item of workand ask the contractors, when tendering, to quote apercentage above or below the given scheduledrates
� when it is above, it is called premium
� and when below, it is called rebate or discount)� and when below, it is called rebate or discount)
When a contract includes both scheduled and non-scheduled items then the contractors are asked toquote an overall premium on the total cost ofscheduled items but, as regards the non-scheduleditems are concerned, the contractor will mention theitem-rates and no extra premium would bepermissible.
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3333---- LumpLumpLumpLump SumSumSumSum ContractContractContractContract
In a Lump Sum Contract, the contractor undertakes to executecertain specified works for a fixed amount of money.
� The nature and extent of the work are normally indicated ondrawings
� The nature of materials and workmanship are described inspecificationsBut no BOQ is provided.
4444---- LabourLabourLabourLabour ContractContractContractContract4444---- LabourLabourLabourLabour ContractContractContractContract
� This is a contract where labour is provided by thecontractor but all the materials are supplied by the client.
� It is suitable for those cases where an employer is in aposition to buy large quantities of materials at favourableprices.
� The advantage is that the speed of work will be increasedbut, at the same time, there will be more wastage ofmaterials.
Labour rates for the scheduled items are also given in the42
5555---- CostCostCostCost PlusPlusPlusPlus PercentagePercentagePercentagePercentage ContractContractContractContract
� In the cost plus percentage contract, the accounts areproperly maintained by the contractors showing the actualexpenditure on the work.
� This is supported by proper receipts and invoices (bills,cash memos, etc).
� The profit of the contractor is decided as a negotiatedpercentage, which may vary from 10 to 25% of theactual cost of contract.
6666---- CostCostCostCost PlusPlusPlusPlus FixedFixedFixedFixed ProfitProfitProfitProfit ContractContractContractContract
This is similar to the previous type of contract with thedifference that the amount of profit is fixed and will not varywith increase or decrease of actual cost of the work. Propermaintenance of accounts by the contractor is must. However,in this category, the contractor will try to complete the workas early as possible.
Cost plus percentage and cost plus fixed profit contractors aretogether called ‘Reimbursement contracts”.
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7777---- PackagePackagePackagePackage DealDealDealDeal ContractContractContractContract
� If a contracting firm is well-reputed and provides bothdesign and construction facilities, the project as a whole maybe awarded to this firm; the agreement become a “PackageDeal Contract”.
� Special type of buildings such as hotels, picture houses,shopping plazas, etc., may be built on the basis of packagedeal contract. However, the success of such a contract mostlydeal contract. However, the success of such a contract mostlydepends upon the reputation and understanding of the firmwith the client.
8888---- SerialSerialSerialSerial ContractContractContractContract
� If a contractor is already working on certain contracts ata construction site and later on more works are planned on thesame site, these works may be awarded to the samecontractor,
� Generally at the same rates, depending upon his previousperformance. This becomes a serial contract
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