METHODOLOGY / PROCEDURE OF CONVENTIONAL SHUTTERING & CONCRETING WORK

METHODOLOGY / PROCEDURE OF CONVENTIONAL SHUTTERING 

& CONCRETING  WORK

 

TERMINOLOGY OF FORMWORK :

 

Ø  Formwork (Shuttering)  - Mould to contain the wet concrete in the desired shape.

Ø  False work (staging, cantering) - Temporary structure to support a permanent structure during erection and until it becomes self supporting.

Ø  Scaffolding (Paranja) - Light structural “Framework” for easy access of workmen.

Ø  Striking (Stripping)  - Scientific dismantling and removing formwork (pre-planned).

Ø  Sheeting (Sheathing)  Supporting membrane in contact with the wet concrete.

Ø  oist (Batten)  Horizontal member supporting sheeting (slabs & beams).

Ø  Bearer (Runner) Horizontal member supporting joists.

Ø  Prop cap  Seating for bearer. (Axial load)

Ø  Prop Vertical member supporting bearer

Ø  Prop base  Seating for prop( Punching shear).

Ø  Prop footing (Spreader)  Member transferring all loads on unyielding strata.

Ø  Wedge  Packing piece used for correct levelling & easy striking of formwork.

Ø  Wailing or Waling  Horizontal member resisting hydrostatic concrete load on sheeting (vertical walls)

Ø  Stud Vertical member resisting hydrostatic concrete loads on sheeting. (Walls).

Ø  Soldier Vertical supporting member cantilevered from previous concrete.

Ø  Yoke a) For columns - Horizontal frame support encircling formwork.

Ø  b) For slip form - Vertical frame support straddling inner & outer formwork.

Ø  Stop-end (Bulkhead) Vertical formwork to form a construction joint in concrete.

Ø  Back form Formwork to the top surface of a sloping slab

Ø  Bracings :

§  Horizontal - Member in 2 direction slenderness ratio of props.

§  Diagonal - Member transferring horizontal and wind loads through props.

Ø  Tie Bolt Interconnecting two opposite formworks to resist hydrostatic loads.

Ø  Riband Horizontal member laid flat to resist horizontal pressure from formwork.

Ø  Starter (Kicker) Small height of wall or column cast along with the footing.

Ø  “C” clamps To hold the 2 opposite formwork or to hold the two right angle formwork.

Ø  Four way head To support to I-section beams below slab or beam bottom.

Ø  Tripod To keep prop in exact plumb & position.

     

  REQUIREMENTS OF SHUTTERING MATERIALS

 

Ø  Standards (Cup lock Verticals)

Ø  Ledgers (Horizontals)

Ø  Base Jack

Ø  Aluminium Primary Beam

Ø  Aluminium Secondary Beam

Ø  Top Jack

Ø  Drop Head

Ø  Wooden Runner

Ø  CT Props

Ø  Bracings

Ø  Brackets

Ø  Tie bars

Ø  Plywood, Runner

Ø  Required size of nails etc.

 

WORK METHODOLOGY / PROCEDURE OF CONVENTIONAL SHUTTERING WORK

 

General:

 

Ø  The Shuttering drawings shall be checked for details prior to execution of work.

Ø  The Shuttering scheme shall be prepared and submitted to the Client for approval.

Ø  The architectural drawings are also checked and compared accordingly.

Ø  In case any details are missing, request for information shall be raised.

Ø  After studying the structural drawings, the Project Engineer/Construction Engineer will plan for sizes, numbers and type of formwork to be used.

Ø  Type of shuttering shall be finalized as per structure before start of shuttering activities.

Ø  Scheme drawing shall be finalized and approved by client or consultant.

Ø  The availability of the material in the shuttering yard shall be checked by the Sectional In-charge.

Ø  All formwork activities will be carried out in accordance with the Project specification.

Ø  During fabrication/Making of formwork shutters, all dimensions shall be cross-checked with a view to avoiding corrective action during erection.

 

Vertical Elements (Columns & Core walls)

      

    

Ø  For starter, 12mm Ply and 3’’x2’’ Runners shall be placed on the layout marked by the surveyor and fixed suitably as per the vertical element layout.

Ø  The starter shall be checked for its verticality and the surface in and around shall be cleaned.

Ø  The starters once prepared are to be checked by concern engineer in-charge.

Ø  Once starter hardens Forms work shall be checked to conform to the shapes, lines, grades and dimensions of concrete as per drawing.

Ø  The wall forms that form the sides of the vertical elements shall be made from 12mm thick approved plywood / Customized Mivan column boxes with accessories or as per project specification.

Ø  The column boxes for these elements shall be fixed as per the shuttering scheme.

Ø  The Plywood column boxes shall be fixed on secondaries runners as per the locations mentioned in the shuttering scheme drawing.

Ø  Shuttering Oil is applied on the panel inner sides to facilitate de-moulding after casting.

Ø  The Wall Panels are held in place by using ISMC Channels of desired size or steel wallers as per the shuttering scheme.

Ø  The Panels are held together vertically using the Tie rods fixed in between the wallers as shown in the shuttering scheme.

Ø  Alignment props are provided to align the vertical shutters in Place.

Ø  Once the above steps are complete, the vertical shutters are ensured of their stability and plumb is checked using plumb bob.

Ø  The shuttering is then checked by the Engineer-in-charge and called client for final inspection.

Ø  Once the client approves the shuttering, the concreting with the specified grade may follow as per the respective Work method statement.

Fixing of Adjustable Telescopic Steel Props for Beam & Slab

Ø  Steel props shall be telescopic and adjustable type. Diameter of outside and inside tube and weight shall be as per manufacturer’s literature.

Ø  Generally outer prop is 50 NB (OD 60.3 mm) and inner prop is 40 NB (OD 48.3 mm) of 8 SWG (4mm thick).

Ø  Outer prop shall be provided with a base plate of size 150 x 150 x 5 mm whereas inner prop may be provided with top plate / fork head / U head.

Ø  Props shall be truly vertical with the maximum deviation in plumb.

Ø  There should be minimum 6 threads above and below the sleeve.

Ø  Prop nut shall be provided to outer prop in such a way that it can be easily rotated through full height of sleeve.

Ø  Locking pin (shear pin) shall be of high tensile steel and of minimum 12mm diameter.

Ø  In addition to above props, some mini props (junior props) for supporting concrete members at short heights shall also be procured as per the requirements.

Ø  Props must be braced in both the directions by tubes and double couplers at approximately 250 mm above prop nuts when extended beyond 3.6 meters.

Ø  A prop should not be used if it is bent, rusted or has a bent head or base plate, damaged pin etc.

Bracings and couplers for steel props

 

Ø  Bracing pipe for props shall be generally 40 NB (OD 48.3 mm) tubes.

Ø  Tubes shall be checked for straightness.

Ø  All couplers shall be checked at random for proper fitting over the pipes.

Ø  The cup lock verticals and horizontals shall be assembled as per the shuttering design for the column head / drop slab.

Ø  The stirrup heads shall be fitted on the verticals.

 

Placing of Aluminum Primary & Secondary Beam

 

Ø  The stirrup heads are fitted on the verticals after which aluminium primary shall be placed.

Ø  The aluminium secondary beams are fixed in the primary aluminium as per the spacing mentioned in the design.

Ø  Then the plywood shall be hammered on the secondary beams.

Ø  Similar staging arrangement shall be followed for the beam bottom area.

Ø  Primary runners placed on along the direction of beam.

Ø  Secondary runners placed perpendicular to beam on top of primary runner.

Ø  Beam dimensions to be checked and marked as per GFC drawings and levelled using Spirit Level.

Ø  Then beam side shuttering shall be fixed.

 

Placing of Slab Bottom

     

Ø  Slab bottom level to be fixed with respect to the marking.

Ø  After completion of beam bottom, the same arrangement is followed for the staging and decking for the flat slab.

Ø  On completion of the decking the area shall be checked for level grid wise.

Ø  Once the levels are checked, the shuttering surface shall be cleaned and masking tape shall be applied to all the joints.

Ø  Then Shuttering oil shall be applied on the top surface shuttering ply and the surface shall be ready to receive reinforcement.

Ø Meanwhile, the slab reinforcement bars can be brought into the slab formwork ready for installation.

 

Fixing of Reinforcement steel

Ø Lay the main reinforcement bars of bottom layer of the slab spaced evenly according to design or drawings.

Ø Tie the reinforcement bars at both ends to maintain the spacing.

Ø Lay the distribution bars and tie them to the main reinforcement bars.

Ø After completing the bottom layer of slab reinforcement, allow the MEP contractors to lay the concealed services.

Ø Install bar chairs acting as spacers between top and bottom reinforcements.

Ø Lay the top reinforcements with distribution bars fixed on first and the main reinforcements on the upper layer (transverse direction).

Ø After completing the slab top reinforcements, clean and blow away the dust by using compressed air.

 

Inspection & checking 

Ø Meantime, the surveyor must check the formwork level and install the markings for the concrete level.

Ø After the formwork level measurements are done, furnish the copy from the surveyor and locate the area which varies from the correct level.

Ø After the adjustment is done, do a routine formwork inspection to check the stability of the frames and runners.

Ø Ensure the slab level markers are fixed nice and tight so that it will not move during the concrete pouring operation.

Ø Check all the formwork gaps and ensure that they are plugged before concrete placement. Concrete slurry will flow through the gaps and will lead to grout loss if not rectified.

 

Prior to Concreting

Ø Spray water to the formwork and reinforcements to lower down the temperature.

Ø Prepare the vibrator machine while waiting for the concrete truck to come. It is always good to have a back-up vibrator if in case something goes wrong.

Ø All concrete trucks must report for slump test. The arrival time will be recorded.

Ø Check the slump height whether it is within the tolerance, if not the concrete would be rejected.

Ø Proceed to concrete placement and maintain sufficient light when the operation reaches dusk or even until midnight.

  

Concreting 

Ø  Concreting shall be done as per approved Methodology.

After Concreting

Ø On the next day, check the concrete slab surface and ensure it is sufficiently dry after 12 to 16 hrs. If not, no manpower or material movement shall be allowed until its hard enough.

Ø Spray water and flood the concrete to cure and repeat when it’s needed.

   

Striking the Formwork:

 

·         Always obtain approval before striking the formwork in the form of checklists.

·         Ensure adequate safety measures taken while striking formwork.

·         Cleaning the face of forms shall start as soon as they have been struck.

·         Good storage is essential to ensure that formwork can be used again.

 

STRIPPING TIME

Ø  It is the minimum time before which formwork of freshly laid concrete structure should not be removed.

Ø  It depends on various factors like ambient temperature, type of cement, type of structure etc.

Ø  For ambient temperature of more than 15⁰C and concrete made with OPC cement and crushed stone aggregate stripping time may be followed as a general guideline as per Clause 11.3 of IS: 456-2000.

Ø   

Sr. No:	Description	Stripping Time
1	Vertical formwork for Cols, walls and sides of beams	16 to 24 hours
2	Slabs ( Props Remaining ) (Props to be refixed after removal of formwork)	3 days
3	Beam soffit( Props remaining ) (Props to be refixed after removal of formwork)	7 days
4	Removal of props to slabs:
	a. Spanning up to 4.5 m	7 days
	b. Spanning over to 4.5 m	14 days
5	Removal of props to beam and arches
	a. Spanning up to 6.0 m	14 days
	b. Spanning over 6.0 m	21 days

 

 

% of Props shall be provided at the time of Slab Casting.

If Nth slab running than

Ø  Reproping to the (N-1) slab will be 100%

Ø  N-2 will 70% and N-3 will be 30%

 

TOLERANCES

Tolerances are the specified permissible variation from lines, grade or dimensions given in the drawings. Unless otherwise specified, the following tolerances will be permitted:

Sr. No.	DESCRIPTION	PERMISSIBLE DEVIATIONS
1	Deviation from specified dimension of cross section of column and beams	-6 mm +12 mm
2	Deviation from dimension of footing.	± 10 mm
a)	Dimension in plan	-12 mm +50 mm
b)	Eccentricity	0.02 times the width of footing in the direction of deviation but not more than 50 mm.
c)	Thickness	± 0.05 times specified thickness.
3	Departure from level shown on the drawing.	± 6 mm
4	Deviations Abrupt irregularities/offsets caused by displaced or misplaced formwork lining or supports.	±10 mm
5	Inserts Variation in position along concrete surface In plane position (flush with concrete face)	± 10 mm   ± 5 mm