Top Banner
FORMWORK FORMWORK
42

From work & shuttering

Feb 14, 2017

Download

Engineering

hamidgujjar
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: From work & shuttering

FORMWORKFORMWORKFORMWORKFORMWORK

Page 2: From work & shuttering

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.

Page 3: From work & shuttering
Page 4: From work & shuttering

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.

Page 5: From work & shuttering

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.

Page 6: From work & shuttering
Page 7: From work & shuttering
Page 8: From work & shuttering
Page 9: From work & shuttering
Page 10: From work & shuttering

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.

Page 11: From work & shuttering
Page 12: From work & shuttering
Page 13: From work & shuttering
Page 14: From work & shuttering
Page 15: From work & shuttering

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.

Page 16: From work & shuttering

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.

Page 17: From work & shuttering

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%.

Page 18: From work & shuttering

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.

Page 19: From work & shuttering

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.

Page 20: From work & shuttering

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.

Page 21: From work & shuttering
Page 22: From work & shuttering
Page 23: From work & shuttering

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”

Page 24: From work & shuttering
Page 25: From work & shuttering
Page 26: From work & shuttering

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.

Page 27: From work & shuttering
Page 28: From work & shuttering
Page 29: From work & shuttering

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.

Page 30: From work & shuttering

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.

Page 31: From work & shuttering
Page 32: From work & shuttering

Formwork for Beam & Slab

Floor

Formwork for Beam & Slab

Floor

Page 33: From work & shuttering

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.

Page 34: From work & shuttering
Page 35: From work & shuttering

Formwork failuresFormwork failuresGenerally some unexpected event causes one member to fail,

then others become overloaded or misaligned and the entire

formwork structure collapses.

Page 36: From work & shuttering

Raft foundation formworkRaft foundation formwork

Page 37: From work & shuttering

Raft foundation formworkRaft foundation formwork

Page 38: From work & shuttering

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

Page 39: From work & shuttering

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.

41

Page 40: From work & shuttering

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

Page 41: From work & shuttering

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”.

43

Page 42: From work & shuttering

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

44