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Form Work



For civil engineering students

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Form Work Form Work Presentation Transcript

  • FORM WORK By Kezar Shah BE(Civil Engineering) M.Sc.(Environment) General Manager-MNC Guest Faculty-CTE
  • “ Form work or shuttering is a temporary construction used as a mould for structure, in which concrete is placed & in which it hardens and matures”.
  •  Construction of form work requires lot of time & material.  Cost of form work is 20-25 % of cost of building.  When required strength of concrete is achieved, form work is removed.  operation of removal of form work is called ‘stripping’ • Removed component of form work is reused for another construction. • Such forms whose components are used many times are called „Panel Forms‟. • Forms made for non standard structures which can not be used again is called ‘Stationary Forms’.
  • Classification of formwork 1. Wooden 2. Plywood 3. Steel 4. Combined (wood & steel)
  • Wooden form work  Most common form work  Disadvantage : Possibility of warping, swelling, shrinkage.  Water impermeable coating on wood form work is applied to reduce warping, swelling, shrinking  With impermeable coating shuttering can be removed easily.
  • Steel form work Steel shuttering is used for major work. Advantages: a) It can be put to use for high number of times. b) It provides ease of stripping c) It gives smooth & even concrete surface d) It posses high rigidity e) It is not liable to shrinkage or distortion f) It is costly.
  • Requirements of form work A good form work should satisfy following requirements: a) Material of formwork should be cheap & can be reused many time. b) It should be water proof & should not absorb water from concrete. Shrinkage & swelling should be minimum. c) It should be strong enough to take all loads coming on it (dead load of concrete,live load of labour during pouring, compaction & curing. d) It should be stiff enough so that deflection is minimum. e) It should be light as far as possible f) Surface of form work should be smooth for easy stripping g) All joints of form work should be stiff so that lateral deformation under load is minimum. Joints should be leak proof.
  • Indian Standard of Form work (IS :456-1964) (1) General : The form work :  shall conform to the shape, lines & dimensions as shown on the plans.  Shall be rigid during placing & compacting of concrete.  Water tight to prevent loss of water from concrete. (2) Cleaning & treatment of forms  All rubbish, chippings, saw dust shall be removed from the interior of form work before placing of concrete.  Shall be wetted.
  • Indian Standard of Form work (IS :456-1964) (3) STRIPPING TIME Form work should not removed until good strength has come. Type of form work Time Vertical wall, columns 16-24 hrs Soffit of slab (Prop should be refixed immediately) 3 days Soffit of beam (Prop should be refixed immediately) 7 days Props to slab Span < 4.5 m 7 days Props to slab Span > 4.5 m 14 days Props of beam (Span < 6 m) 14 days Props of beam (Span > 6 m) 21 days
  • Indian Standard of Form work (IS :456-1964) (4) Procedure when removing form work  All form work shall be removed without shock or vibration as it will damage the concrete.  Before the soffit (bottom surface ) & struts (pole) are removed, the concrete shall be exposed, to check that the concrete has sufficiently hardened.  Proper precautions shall be taken to allow for decrease in the rate of hardening in cold water. (5) Camber  It is desirable to give form an upward camber (slope) to ensure that beams do not sag when they have taken up their deflection.  This should be done only when allowed in the design calculation of the beam.
  • Indian Standard of Form work (IS :456-1964) (6) Tolerances Form work shall be so constructed that the internal dimen sions are within the permissible tolerance specified by the designer.
  • LOADS ON FORM WORK The form work has to take following loads: a) Live load due to labour b) Weight of wet concrete c) Hydrostatic pressure of the fluid concrete acting against the vertical or inclined faces of form d) Impact due to pouring of concrete.  Live loads of labour & equipment including impact may be taken as 370 Kg/m2.
  • LOADS ON FORM WORK HYDROSTATIC PRESSURE: Hydro static pressure due to fluid of concrete depends on : a) Quantity of water in concrete b) Size of aggregate c) Rate of pouring d) Temperature
  • HYDROSTATIC PRESSURE: Hydrostatic pressure is maximum during pouring and decreases when concrete becomes hard. Setting time may be taken as ¾ to 1 hour. Only height of concrete poured in ¾ to 1 hour is taken into account for calculation of hydrostatic pressure on form work. For 1.5 m height of concrete, equivalent weight of concrete may be taken as 2300 kg/m3.
  • • HYDROSTATIC PRESSURE: For higher height, the equivalent weight of concrete is reduced. When height of concrete in one pour is 6 m, the equivalent fluid weight may be 1200 kg/m3. For intermediate heights between 1.5 to 6 m poured within the setting time of ¾ hour linear interpolation of unit weight between 1200 to 2300 kg/m3 may be taken.
  • SHUTTERING FOR COLUMN It consists of : a. Sheeting all round the column periphery b. Side yokes & end yokes c. Wedges d. Bolts with washers
  • SHUTTERING FOR COLUMN  The side yokes & end yokes consists of 2 numbers each  They are suitably spaced along the height of column  Two side yokes are comparatively of heavier section & are connected together by 2 long bolts.  Four wedges one at each corner are inserted between bolts & end yokes  The sheathing is nailed to yokes.
  • SHUTTERING FOR BEAM & SLAB FLOOR  The slab is continuous over number of beams.  The slab is supported on 2.5 cm thick sheathing laid parallel to main beam.  The sheathing is supported on wooden battens which are laid between the beams, at suitable spacing.  In order to reduce deflection, the battens may be propped at middle of the span through joists.  The side forms of the beam consists 3 mm thick sheathing.  The bottom sheathing of the beam form may be 5 to 7 cm thick.
  • SHUTTERING FOR BEAM & SLAB FLOOR  The end of the battens are supported on ledger which is fixed to cleats throughout the length.  Cleats 10 cm x 2 cm x 3 cm are fixed to the forms at the same spacing as that of battens, so that battens may be fixed to them.  The beam forms is supported on a head tree.  The shore or post is connected to head tree through cleats.  At the bottom of shore, two wedges of hard wood are provided over a sole piece.
  • SHUTTERING FOR STAIRS • The sheathing or decking for deck slab is carried on cross joists • Cross joists are supported on raking ledgers. • Ledger is 7.5 cm x 10 cm size. • Cross joists are 5 cm x 10 cm size • Riser planks are 4 -5 cm thick • Planks are bevelled at bottom to permit the whole of the tread faced to be trovelled.
  • SHUTTERING FOR STAIRS • Riser plank are fixed after reinforcement has been fixed in position. • Outer end of of risers are carried vby a cut string made of 5 cm plank. • The cut string is strutted to the cross joists by 5 cm x 10 cm struts. • The wall ends of the riser planks are carried by 5 cm x 10 cm hangers secured to 5 cm thick board fixed to wall. • Treads are left open for concreting & vibration. • Stiffer joists of 5 cm x 10 cm is placed along the middle of the riser planks. • Stiffner is wired to cross joists through decking.
  • Thank you 31