Bb Formwork

11

FormworkFormwork DefinitionDefinition A structure, usually temporary (but sometimes A structure, usually temporary (but sometimes

wholly or partly permanent), used to contain wholly or partly permanent), used to contain poured concrete to mould it to required poured concrete to mould it to required DIMENSIONS, FINISHES and SUPPORT it DIMENSIONS, FINISHES and SUPPORT it until it is able to support itself.until it is able to support itself.

Formwork consists of contact face material and Formwork consists of contact face material and the bearers which support the face material.the bearers which support the face material.

22

Code of Practice for Formwork Code of Practice for Formwork DesignDesign

Concrete Pressure ComputationConcrete Pressure Computation:: Concrete Pressures on Formwork, Concrete Pressures on Formwork,

CIRIA Report 108 (Ref.)CIRIA Report 108 (Ref.) Design PracticeDesign Practice:: Formwork Formwork –– a Guide to Good Practice, a Guide to Good Practice,

published by Concrete Society and published by Concrete Society and IStructE (Ref.)IStructE (Ref.)

33

Common Types of FormworkCommon Types of Formwork Wall FormWall Form

44

Common Types of FormworkCommon Types of Formwork

WallWall

FormForm

55


Column FormColumn Form ..\Teaching_Notes\TEMP_WK\multimedia\Columnfo

rm1.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Columnfo



rm1003.jpg

66


Soffit FormSoffit Form ..\Teaching_Notes\TEMP_WK\multimedia\So

ffit Form Frame.jpg ..\Teaching_Notes\TEMP_WK\multimedia\So

ffit Form Frame001.jpg

77


Beam FormBeam Form ..\Teaching_Notes\TEMP_WK\multimedia\Beam Form-Edge004.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Beam Form005.jpg

Stair FormStair Form Permanent FormworkPermanent Formwork

88

Combined formwork and Combined formwork and falseworkfalsework

Formwork and falsework can be combined into a single Formwork and falsework can be combined into a single handleable unithandleable unit

Time could be saved in erection and stripping and the Time could be saved in erection and stripping and the labor content of the operation thus significantly reducedlabor content of the operation thus significantly reduced

Large repetition is a must for this method to be effective. Large repetition is a must for this method to be effective. Common examples include:Common examples include:

Table FormTable Form..\Teaching_Notes\TEMP_WK\multimedia\Tableform2.jpg, , Flying Flying

FormForm..\Teaching_Notes\TEMP_WK\multimedia\FlyingForm2.jpg,, Travelling FormTravelling Form..\Teaching_Notes\TEMP_WK\multimedia\Travelform.jpg

Usually they are available from specialist suppliersUsually they are available from specialist suppliers

99

FormworkFormwork

Three general principles govern Three general principles govern formwork design and formwork design and construction:construction:

QUALITYQUALITY SAFETYSAFETY ECONOMYECONOMY

1010

Quality of FormworkQuality of Formwork

Relating to the formed faces of the Relating to the formed faces of the permanent concrete structure and permanent concrete structure and refers to the following two aspects:refers to the following two aspects:

AccuracyAccuracy of Concrete Shape of Concrete Shape QualityQuality of Concrete Surface of Concrete Surface

1111

Quality of FormworkQuality of FormworkAccuracyAccuracy is controlled by the is controlled by the deviations permitted (Tolerances) deviations permitted (Tolerances) in the :in the :

Formwork deflectionFormwork deflection MaterialsMaterials ComponentsComponents WorkmanshipWorkmanship

1212


To minimise deviations, all formwork To minimise deviations, all formwork must have adequate means of:must have adequate means of:

Alignment and adjustment both at Alignment and adjustment both at construction joints and throughout the construction joints and throughout the formwork formwork

e.g. Simple wedges, screw adjustments e.g. Simple wedges, screw adjustments on supports, camber adjustmentson supports, camber adjustments

1313


Failures in achieving surface quality are Failures in achieving surface quality are often caused by:often caused by:

Lack of formwork stiffness to resist the Lack of formwork stiffness to resist the movement coming from concrete vibrators movement coming from concrete vibrators during concrete placement and the during concrete placement and the subsequent grout loss at the joints (honey-subsequent grout loss at the joints (honey-combing, harder stripping)combing, harder stripping)

Concrete shape, disposition of steel barsConcrete shape, disposition of steel bars Efficiency of conc. placement, forms Efficiency of conc. placement, forms

strippingstripping

1414


Classes of FinishesClasses of Finishes Formed FinishesFormed Finishes F1, F2, F3, F4, F5 (CED G.S. Table 14.1) F1, F2, F3, F4, F5 (CED G.S. Table 14.1) ––

Class F5 the bestClass F5 the best Unformed FinishesUnformed Finishes U1, U2, U3, U4, U5 (CED G.S. Table 14.2) U1, U2, U3, U4, U5 (CED G.S. Table 14.2) ––

Class U5 the bestClass U5 the best Treated FinishesTreated Finishes T1, T2, T3, T4, T5, T6 (CED G.S. Table 14.3)T1, T2, T3, T4, T5, T6 (CED G.S. Table 14.3)

1515


Different concrete structures buried Different concrete structures buried underground or exposed to naked eyes underground or exposed to naked eyes require different class finishes specified require different class finishes specified by the contract documentby the contract document

The formwork design requires The formwork design requires appropriate method of appropriate method of construction/treatment, different surface construction/treatment, different surface irregularities requirements and types of irregularities requirements and types of contact face sheeting materialscontact face sheeting materials

1616


TolerancesTolerances

1717

Safety of FormworkSafety of Formwork

Two major aspects must be Two major aspects must be covered:covered:

Personal Safety of both Personal Safety of both formworkers and the publicformworkers and the public

Safety of the formwork Safety of the formwork structurestructure

1818


I.I. Construction phaseConstruction phaseAs a general practice, the erected formwork As a general practice, the erected formwork shall be :shall be :

Structurally safeStructurally safe Having Having secured and effectivesecured and effective guard rails, guard rails, toeboards, access ladders and stairs around its toeboards, access ladders and stairs around its peripheryperiphery

Formworkers equipped with safety helmets and Formworkers equipped with safety helmets and bootsboots

For high work, safety harnesses and security For high work, safety harnesses and security screen are to be installedscreen are to be installed

1919


II.II. Design phaseDesign phase

a)a) Evaluation of possible Loading Evaluation of possible Loading Combinations occurred in the Combinations occurred in the following stages:following stages:

Stage 1: before conc. PlacementStage 1: before conc. Placement Stage 2: during conc. PlacementStage 2: during conc. Placement Stage 3: after conc. PlacementStage 3: after conc. Placement

2020


b) Structural requirementsb) Structural requirementsThree important aspects to be met:Three important aspects to be met:

STRENGTH (material strength and force STRENGTH (material strength and force equilibrium)equilibrium)

STABILITY (Sliding, overturning, uplift and STABILITY (Sliding, overturning, uplift and sidesway)sidesway)

STIFFNESS (accuracy and permissible STIFFNESS (accuracy and permissible tolerances)tolerances)

2121

Economy of FormworkEconomy of Formwork

Where formwork is highly repetitive Where formwork is highly repetitive activity, a small reduction in activity, a small reduction in fabrication/stripping could result a fabrication/stripping could result a significant overall cost saving.significant overall cost saving.

Cost involves formwork materials and Cost involves formwork materials and labor, erection (including hoisting), labor, erection (including hoisting), stripping, repairing and cleaning of stripping, repairing and cleaning of formwork after concrete pour.formwork after concrete pour.

2222

Economy of FormworkEconomy of Formwork Increase in no. of reuses lower the unit cost Increase in no. of reuses lower the unit cost

of the formworkof the formwork More sophisticated design could be More sophisticated design could be

economically justifiable esp. when less economically justifiable esp. when less maintenance will be required.maintenance will be required.

Good formwork, apart from meeting the Good formwork, apart from meeting the technical specifications requirements, technical specifications requirements, means it is easy to fabricate, erect, adjust, means it is easy to fabricate, erect, adjust, dismantle, and within the available dismantle, and within the available crane/man handling.crane/man handling.

2323

Care of FormworkCare of Formwork

For maximum formwork life, efficient For maximum formwork life, efficient stripping; care in formwork handling, stripping; care in formwork handling, storage, and maintenance are essentialstorage, and maintenance are essential

After stripping, the formwork units for After stripping, the formwork units for reuse should be moved away from the reuse should be moved away from the work area (workers of other trades work area (workers of other trades may damage it as an item of may damage it as an item of obstruction left there).obstruction left there).

2424

Care of FormworkCare of Formwork They should be stored and protected They should be stored and protected

from weather to avoid surface damagefrom weather to avoid surface damage Large formwork panels should be Large formwork panels should be

stacked in racks, facing away from direct stacked in racks, facing away from direct sunlightsunlight

Hardened slurry, dirt left from previous Hardened slurry, dirt left from previous pour should be removed from plywood pour should be removed from plywood sheeting surfaces before they are getting sheeting surfaces before they are getting harderharder

2525

Care of FormworkCare of Formwork Mechanisms, locking devices and fixings Mechanisms, locking devices and fixings

should be cleaned and oiled.should be cleaned and oiled. Face sheeting to be given a coat of release Face sheeting to be given a coat of release

agent agent Care to be taken not to damage the presealed Care to be taken not to damage the presealed

surface of the plywood sheeting (Use a soft surface of the plywood sheeting (Use a soft brush in dust removal and a softwood wedge brush in dust removal and a softwood wedge to remove larger concrete particles)to remove larger concrete particles)

2626

Formwork Striking ProceduresFormwork Striking Procedures--RC Slab FormRC Slab Form

Ease all supports by 1-2 turns for each propEase all supports by 1-2 turns for each prop Starting from mid-span, remove the props Starting from mid-span, remove the props

towards columns or wallstowards columns or walls This will ensure no negative hogging bending This will ensure no negative hogging bending

moment induced in the concrete slab if the last moment induced in the concrete slab if the last few supports were left at the mid-span as few supports were left at the mid-span as intended in the original design. intended in the original design.

Cracking due to reverse bending will occur Cracking due to reverse bending will occur otherwise otherwise

2727

Formwork Striking ProceduresFormwork Striking Procedures--RC Slab on Beam FormRC Slab on Beam Form

Strike the slab soffit form firstStrike the slab soffit form first Then strike the beam soffit starting at mid-span towards Then strike the beam soffit starting at mid-span towards

the columns/wallsthe columns/walls This will ensure that all the imposed vertical load will be This will ensure that all the imposed vertical load will be

supported by the slab which is in turn supported by the supported by the slab which is in turn supported by the beam form plus its falsework. By removing propping to beam form plus its falsework. By removing propping to the beam form at the mid-span, the beam could then the beam form at the mid-span, the beam could then span across the column/wall at both end as intended by span across the column/wall at both end as intended by the original structural design. the original structural design.

Cracking due to reverse bending will occur otherwise. Cracking due to reverse bending will occur otherwise.

2828

Formwork Striking ProceduresFormwork Striking Procedures--RC Cantilever Slab FormRC Cantilever Slab Form

Start the propping striking from the tip Start the propping striking from the tip of the cantilever and work towards the of the cantilever and work towards the column/wall/beam.column/wall/beam.

\Particular care should be observed that \Particular care should be observed that any effect of overloading on the adjacent any effect of overloading on the adjacent spans temporarily when the propping to spans temporarily when the propping to cantilever is not properly striken. cantilever is not properly striken.

2929

Formwork Formwork –– Minimum Period before Striking (BS 8110) Minimum Period before Striking (BS 8110)

FormworkFormwork Surface conc. Surface conc. temperaturetemperature

>16 deg C>16 deg C

Surface conc. Surface conc. temperature temperature

0 0 –– 10 deg C 10 deg C

Column, wall, large beam Column, wall, large beam formform

12 h12 h

Slab formSlab form 4 days4 days

Beam & props to slab Beam & props to slab formform

10 days10 days

Prop to beamProp to beam 14 days14 days

ht 10

300

ht 10

100

ht 10

250

ht 10

360

3030

BackproppingBackpropping

The speed of construction The speed of construction vertically will dictate a number vertically will dictate a number of slab levels acting together to of slab levels acting together to support the total construction support the total construction loads imposed from the topmost loads imposed from the topmost concrete slab casting operationconcrete slab casting operation

3131

BackproppingBackpropping

To avoid excessive loads building To avoid excessive loads building cumulatively in the backprops, cumulatively in the backprops, backprops are loosened after backprops are loosened after striking a slab formwork and then striking a slab formwork and then repositioned and retightened. The repositioned and retightened. The cast floor is thus allowed to take its cast floor is thus allowed to take its deflected shape hence the load deflected shape hence the load imposed from the floor(s) aboveimposed from the floor(s) above

3232

Formwork MaterialsFormwork Materials

Face Contact Materials (features left*)Face Contact Materials (features left*) Sawn board formwork (sawmarks*)Sawn board formwork (sawmarks*) Plywood (fine & smooth surface*)Plywood (fine & smooth surface*) Steel form (variable color*)Steel form (variable color*) Aluminium form (react with cement*)Aluminium form (react with cement*) Glass fibre reinforced plactics (highest quality Glass fibre reinforced plactics (highest quality

for sculptured profiles*)for sculptured profiles*)* features/drawback* features/drawback

3333


Waling/Bearer, Soldier/Props MaterialsWaling/Bearer, Soldier/Props Materials Solid timber Solid timber Steel in lattice configurations or cold Steel in lattice configurations or cold

formed sections (standard/proprietary)formed sections (standard/proprietary)

Aluminium (Al Alloys) sections Aluminium (Al Alloys) sections

3434


Expanded metal (stopends)Expanded metal (stopends) ..\Teaching_Notes\TEMP_WK\multi

media\expanded metal formwork.tif

3535

Proprietary Formwork SystemProprietary Formwork System

Basic Panel system Basic Panel system –– generally no walings, but generally no walings, but complete with corner panels, access brackets, complete with corner panels, access brackets, stabilisersstabilisers

Table forms Table forms ..\Teaching_Notes\TEMP_WK\multimedia\Tableform2.jpg

Flying formsFlying forms ..\Teaching_Notes\TEMP_WK\multimedia\FlyingForm2.jpg

Slab support systemSlab support system ..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Modular Frame .jpg ..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Modular Frame.jpg

Waffle and trough mouldsWaffle and trough moulds Composite Floors with Steel DeckingComposite Floors with Steel Decking

3636

Form TiesForm Ties

Recoverable and non-recoverable typesRecoverable and non-recoverable types ..\Teaching_Notes\TEMP_WK\multimedia\Wall Tie001.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Wall tie002.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Wall tie003.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Wall tie004.jpg

Tie rods are the most critical parts in the formwork Tie rods are the most critical parts in the formwork design which will lead to the complete formwork design which will lead to the complete formwork failure if any of them failsfailure if any of them fails

3737

Form TiesForm Ties

Factor of safety in tension capacityFactor of safety in tension capacity

1)1) 1.5 for HT cold worked steel1.5 for HT cold worked steel

2)2) 2.5 for mild steel2.5 for mild steel Bearing plates/washers to be checked if Bearing plates/washers to be checked if

bearing stresses acting on the timber bearing stresses acting on the timber waling/soldiers are exceeded or notwaling/soldiers are exceeded or not

Limitation on spacing of form ties is also a Limitation on spacing of form ties is also a concern for aesthetic reasonsconcern for aesthetic reasons

3838

Formwork Design Formwork Design –– Concrete pressureConcrete pressure

FactorsFactors IncreaseIncrease PressurePressure

ChangesChanges

Cement Types/Cement Types/

Mix Composition (CMix Composition (C22))

Retarder,Retarder,

PFAPFA

Rate of Pour (R)Rate of Pour (R)

Size & Shape of Formwork (CSize & Shape of Formwork (C11)) Column, Column, WallWall

Height of Form (H)Height of Form (H)

Concrete Temperature at Placing (T)Concrete Temperature at Placing (T)

Unit Weight of Conc. (D)Unit Weight of Conc. (D)

3939

Concrete pressure distribution Concrete pressure distribution along a vertical wall form along a vertical wall form

(Trapezoidal)(Trapezoidal)

Concrete is still hydrostatic

Concrete has been hardening

Pmax

4040

Concrete Pressure Formula Concrete Pressure Formula (CIRIA Report 108)(CIRIA Report 108)

CC22 is coefficient depending on mix ingredients is coefficient depending on mix ingredients D is unit weight of concrete, kN/m3D is unit weight of concrete, kN/m3 CC11 is coefficient depending on form size & shape is coefficient depending on form size & shape H is vertical form height, mH is vertical form height, m K is temperature coefficientK is temperature coefficient R is rate at which conc. rises vertically, m/hR is rate at which conc. rises vertically, m/h

2

16

36

TK

RHKRDP 5.145.05.1max o r D h

in kP a w h ichever is TH E S M A LLE R

2

16

36

TK

4141

Formwork Design - LoadingFormwork Design - Loading

Self-weightSelf-weight of Formwork of Formwork Imposed LoadsImposed Loads (permanent work loads and (permanent work loads and

construction operation loads)construction operation loads) Concrete PressureConcrete Pressure (for wall/column forms) (for wall/column forms) Environmental LoadsEnvironmental Loads (Wind loads, Snow/Ice (Wind loads, Snow/Ice

Loads)Loads) Horizontal LoadsHorizontal Loads (Imposed plant loads, skip (Imposed plant loads, skip

impact loads,.. And minimum horizontal stability impact loads,.. And minimum horizontal stability force i.e. 10% of the total form self-weight)force i.e. 10% of the total form self-weight)

4242

Formwork Design -Formwork Design -

Design procedures follow the design of Design procedures follow the design of permanent works but:permanent works but:

1)1) Permissible stress design method are often Permissible stress design method are often used;used;

2)2) Higher working material stressesHigher working material stresses3)3) Formwork system will include Formwork system will include

manufacturing and assembly tolerancesmanufacturing and assembly tolerances

4343

Formwork Design Formwork Design –– Soffit Form StabilitySoffit Form Stability

Stability of soffit formwork Stability of soffit formwork erected at the top of falsework is erected at the top of falsework is covered in BS5975 (formwork is covered in BS5975 (formwork is considered as an integral part of considered as an integral part of the falsework)the falsework)

4444

Formwork Design Formwork Design –– Wall Form StabilityWall Form Stability

Stability of freestanding wall forms Stability of freestanding wall forms must be checked for the following must be checked for the following three scenarios:three scenarios:

1)1) Maximum Wind and Nominal access Maximum Wind and Nominal access Loads on any working platform (W/P)Loads on any working platform (W/P)

2)2) Working Wind and Full Construction Working Wind and Full Construction Operation Loads on any W/POperation Loads on any W/P

4545

Formwork Design Formwork Design –– Wall Form StabilityWall Form Stability

3)3) Minimum Stability Force and Full Minimum Stability Force and Full Construction Operation Loads on any Construction Operation Loads on any W/PW/P

Note: Working wind means the upper Note: Working wind means the upper wind speed limit below which operations wind speed limit below which operations could still be allowed could still be allowed

4646

Formwork Design Formwork Design –– Design Design ConceptsConcepts

Single Face FormworkSingle Face Formwork Cantilevered FormworkCantilevered Formwork Discontinuity in Face Sheeting and Discontinuity in Face Sheeting and

SoffitSoffit Impact against a fixed face/joint during Impact against a fixed face/joint during

concretingconcreting Inclined SoffitsInclined Soffits Cantilevered SoffitsCantilevered Soffits

4747

Special FormworkSpecial Formwork

SlipformsSlipforms ..\Teaching_Notes\TEMP_WK\multimedia\Slipform.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Slipform001.jpg

ClimbformsClimbforms.

.\Teaching_Notes\TEMP_WK\multimedia\ClimbForm.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Climbform3.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Climbform4.jpg

TravellersTravellers ..\Teaching_Notes\TEMP_WK\multimedia\Travelform.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Travelform1.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Travelform2.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Travelform3.jpg

4848

Special FormworkSpecial Formwork

Tilt-up MouldsTilt-up Moulds ..\Teaching_Notes\TEMP_WK\multimedia\Tilt-up Mould.tif

Gang FormsGang Forms ..\Teaching_Notes\TEMP_WK\multimedia\Gangform1.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Gangform2.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Gangform3.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Gangform4.jpg

Moulds for Prestressed ConcreteMoulds for Prestressed Concrete Tunnel FormTunnel Form ..\Teaching_Notes\TEMP_WK\multimedia\Tunnel Form.tif

4949

Special Formwork DetailsSpecial Formwork Details

Kickers for wall formKickers for wall form ..\Teaching_Notes\TEMP_WK\multimedia\Kicker.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Kicker001.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Kicker002.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Kicker003.jpg

Kickers for column formKickers for column form ..\Teaching_Notes\TEMP_WK\multimedia\Column Kicker.tif

Stopend forms for wall formStopend forms for wall form ..\Teaching_Notes\TEMP_WK\multimedia\Stopend Form.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Stopend Form.tif ..\Teaching_Notes\TEMP_WK\multimedia\Stopend Form001.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Stopend Form002.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Stopend Form003.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Stopend Form004.jpg

5050


Wall TiesWall Ties ..\Teaching_Notes\TEMP_WK\multimedia\Wall Tie.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Wall Tie001.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Wall tie002.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Wall tie003.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Wall tie004.jpg..\Teaching_Notes\TEMP_WK\multimedia\Wall tie004.jpg

PropsProps ..\Teaching_Notes\TEMP_WK\multimedia\Prop.jpg..\Teaching_Notes\TEMP_WK\multimedia\Prop.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Prop001.jpg..\Teaching_Notes\TEMP_WK\multimedia\Prop001.jpg

U-headU-head ..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form U-head.jpg..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form U-head.jpg

Sloping soffit formSloping soffit form ..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Sloping Details.jpg..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Sloping Details.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Sloping Details001.jpg..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Sloping Details001.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Sloping Details002.jpg..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Sloping Details002.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Sloping Details003.jpg..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Sloping Details003.jpg

5151


Bracing for soffit formBracing for soffit form ..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Frame Bracing.jpg..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Frame Bracing.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Bracing Connector.jpg..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Bracing Connector.jpg

Bracing for beam formBracing for beam form ..\Teaching_Notes\TEMP_WK\multimedia\Beam-Soffit Form.tif..\Teaching_Notes\TEMP_WK\multimedia\Beam-Soffit Form.tif

Bracing for column formBracing for column form ..\Teaching_Notes\TEMP_WK\multimedia\Columnform Bracing.jpg..\Teaching_Notes\TEMP_WK\multimedia\Columnform Bracing.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Columnform Bracing001.jpg..\Teaching_Notes\TEMP_WK\multimedia\Columnform Bracing001.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Columnform Bracing002.jpg..\Teaching_Notes\TEMP_WK\multimedia\Columnform Bracing002.jpg ..\Teaching_Notes\TEMP_WK\multimedia\Columnform Bracing003.jpg..\Teaching_Notes\TEMP_WK\multimedia\Columnform Bracing003.jpg

5252

Slipforms Slipforms –– features features

The system is intended for continuous The system is intended for continuous concreting work for walls of constant section.concreting work for walls of constant section.

The shutter rises from 150 to 300 mm per The shutter rises from 150 to 300 mm per hour depending on the rate of concrete hour depending on the rate of concrete hardening.hardening.

5353

Slipforms Slipforms –– features features

The form is about 900-1200 mm deep, The form is about 900-1200 mm deep, fixed to and held apart by timber or steel fixed to and held apart by timber or steel frame or yokes as shown in the figure on frame or yokes as shown in the figure on the right.the right.

On top of each yoke is fixed a hydraulic On top of each yoke is fixed a hydraulic jack which climbs along a steel jacking jack which climbs along a steel jacking rod, about 25 mm in diameter, which is rod, about 25 mm in diameter, which is cast into the wall.cast into the wall.

5454

Slipforms Slipforms –– Operation Operation ProceduresProcedures

(i) Fix steel reinforcement above the (i) Fix steel reinforcement above the shuttershutter

(ii) Pour concrete into the shutter and (ii) Pour concrete into the shutter and vibrate it in final positionvibrate it in final position

(iii) Operate the jack to work against (iii) Operate the jack to work against the lower jaws to raise the yoke and the the lower jaws to raise the yoke and the form with itform with it

5555

Slipforms Slipforms –– Operation Procedures Operation Procedures

(iv) When the oil pressure is released, (iv) When the oil pressure is released, the upper jaws grip under the action of the upper jaws grip under the action of a springa spring

(v) The jack is operated in cycles (iii) + (v) The jack is operated in cycles (iii) + (iv) and each cycle gives a rise of about (iv) and each cycle gives a rise of about 25 mm25 mm

5656

Slipform Slipform –– Uses and Limitations Uses and Limitations

UsesUses The process is used for constructing The process is used for constructing

concrete chimneys, silos, shaft linings, concrete chimneys, silos, shaft linings, towers and building cores and bridge towers and building cores and bridge pierspiers

Possible to vary wall thickness and Possible to vary wall thickness and layout over the height (despite overall layout over the height (despite overall cost will be increased)cost will be increased)

5757


LimitationsLimitations Steady and continuous concreting must Steady and continuous concreting must

be maintained throughout the processbe maintained throughout the process Longer duration and sophisticated Longer duration and sophisticated

equipment layout in the initial setupequipment layout in the initial setup High capital cost in the plant & High capital cost in the plant &

equipmentequipment

5858


LimitationsLimitations Labors working in shifts and hence Labors working in shifts and hence

higher labor costshigher labor costs No construction jointsNo construction joints Working platform to be protected from Working platform to be protected from

adverse weather e.g. high wind, heavy adverse weather e.g. high wind, heavy pourspours

5959


LimitationsLimitations Standby plant and operatives are neededStandby plant and operatives are needed Openings formed by timber/polystyrene Openings formed by timber/polystyrene

within a film of concrete on each face could within a film of concrete on each face could avoid displacement of the former during the avoid displacement of the former during the vertical sliding processvertical sliding process

It requires specialist working and It requires specialist working and supervision operatives supervision operatives

6060

Tilt-up MouldsTilt-up Moulds

The unit mould is cast horizontally and may The unit mould is cast horizontally and may subsequently be tilted through a designed subsequently be tilted through a designed angleangle

The vertical position of the cast unit on The vertical position of the cast unit on completion of demoulding could facilitate easy completion of demoulding could facilitate easy and early formwork removal, and the and early formwork removal, and the subsequent vertical stackingsubsequent vertical stacking

Horizontal processing could allow easy tiling Horizontal processing could allow easy tiling works, or composite sandwich/hollow units works, or composite sandwich/hollow units manufacturemanufacture

6161

Moulds for Prestressed ConcreteMoulds for Prestressed Concrete

Sideforms which cannot be removed Sideforms which cannot be removed before prestressing operations before prestressing operations commence should be designed to commence should be designed to allow vertical and horizontal allow vertical and horizontal movement of the cast member during movement of the cast member during prestressingprestressing

Safety rules to all personnel Safety rules to all personnel concerned must be adhered to during concerned must be adhered to during the tendon stressing operationthe tendon stressing operation

6262

Formwork ChecklistFormwork Checklist

Design concept in relation to Design concept in relation to expected concreting rateexpected concreting rate

Material strength, stiffness, Material strength, stiffness, condition and dimensionscondition and dimensions

Access Access –– adequate space, adequate space, guardrails, toeboards, ladder/stairsguardrails, toeboards, ladder/stairs

6363

Formwork ChecklistFormwork Checklist Assembly - layout dimensions, plumb & Assembly - layout dimensions, plumb &

stability, inserts fixed, ties tightened and stability, inserts fixed, ties tightened and thread conditions checked, sealed against thread conditions checked, sealed against kicker, panel joints sealed, waterstop kicker, panel joints sealed, waterstop installed, filling over nail holesinstalled, filling over nail holes

Release agent appliedRelease agent applied Formwork cleaned outFormwork cleaned out Stripping Stripping –– nails bent/removed, resuable nails bent/removed, resuable

materials separatedmaterials separated

Bb Formwork

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