FORM WORK FORM WORK CENTRING AND SHUTTERING Form

FORM WORK

FORM WORK (CENTRING AND SHUTTERING) Form work, also termed as false work in IS: 14687, shall include all temporary or permanent forms or moulds required forming the concrete which is cast-in-situ, together with all temporary construction required for their support. For detailed Guidelines on Form work for Concrete structures, IS: 14687 may be referred to.

4. 2. 2 Design & Tolerance in Construction Form work shall be designed and constructed to the shapes, lines and dimensions shown on the drawings with the tolerances given below. (Clause 9. 6 of IS: 14687) a) Deviation from specified dimension of cross section of Columns and beams : + 12 mm to - 6 mm b) Deviation from dimensions of footings i) Dimension in Plan : + 50 mm to - 12 mm ii) Eccentricity in plan : 0. 02 times the width of footings in the direction of deviation but not more than 50 mm. iii) Thickness : + 0. 05 times the specified thickness. (Note : Tolerances apply to concrete dimensions only and not to positioning of vertical steel or dowels).

Pressure on Formwork : Rate of placement & Temperature

General Requirement a) Forms shall be designed to ensure safety of permanent constructions and of workmen. b) The design of form work shall conform to sound Engineering practices and relevant IS codes. It shall be strong enough to withstand the dead and live loads and forces caused by ramming and vibrations of concrete and other incidental loads, imposed upon it during and after casting of concrete.

Screw jacks or hard board wedges where required shall be provided to make up any settlement in the form work either before or during the placing of concrete. It shall be made sufficiently rigid by using adequate number of ties and braces.

c) Forms shall be so constructed as to be removable in sections in the desired sequence, without damaging the surface of concrete or disturbing other sections. Care shall be taken to see that no piece is keyed into the concrete.

d) The scheme of Form work should facilitate adequate and safe access to all areas for inspection.

e) The Form work shall be erected such that the shape and dimensions of the Concrete Structures conform to the drawings, the specifications and tolerances. Cambers, bevelled edges and mouldings if specified should be provided in the Form. f) It should not leak while poring the concrete.

g) Commercially available Form work may be used provided they satisfy the requirements mentioned in IS: 14687 -1999.

IS 14687 : 1999 for FALSEWORK FOR CONCRETE STRUCTURES - GUIDELINES Removal of Form work (Stripping time) In normal circumstances and where ordinary Portland cement is used, forms may generally be removed after the expiry of the following periods. (Based on Clause 9. 5. 1 of IS: 14687 -1999)

Type of Formwork (a) Vertical formwork to columns, walls, beams Minimum Period before striking Form work 16 – 24 hours (b) Soffit formwork to slabs (Props to be re-fixed immediately after removal of formwork) 3 days (c ) Soffit formwork to - beams (Props to be re-fixed immediately after removal of formwork) 7 days (d) Props to slabs (1) Spanning up to 4. 5 m (2) Spanning over 4. 5 m 7 days 14 days (e) Props to beams and arches: (1) Spanning up to 6 m (2) Spanning over 6 m 14 days 21 days

Note 1 For other types of cement, the stripping time recommended for ordinary Portland cement may be suitably modified. If Portland Pozzolana or low heat cement has been used for concrete, the stripping time will be 10/7 of the period stated above. Note 2 The number of props left under, their sizes and disposition shall be such as to be able to safely carry the full dead load of the slab, beam or arch as the case may be together with any live load likely to occur during curing or further construction.

Measurements General The form work shall include the following: a. Splayed edges, notching, allowance for overlaps and passing at angles, sheathing battens, strutting, bolting, nailing, wedging, easing, striking and removal. b. All supports, struts, braces, wedges as well as mud sills, piles or other suitable arrangements to support the form work. c. Bolts, wire ties, clamps, spreaders, nails or any other items to hold the sheathing together.

d. Working scaffolds, ladders, gangways and similar items. e. Filleting to form stop chamfered edges of splayed external angles not exceeding 20 mm wide to beams, columns and the like. f. Where required, the temporary openings provided in the forms for pouring concrete, inserting vibrators, and cleaning holes for removing rubbish from the interior of the sheathing before pouring concrete.

g. Dressing with oil to prevent adhesion and h. Raking or circular cutting.

Area to be measured Where it is stipulated that the form work shall be paid for separately, measurements shall be taken of the area of shuttering in contact with the concrete surface. Dimensions of the form work shall be measured correct to a cm.

4. 2. 6. 3 Classification of Measurements The measurements shall be taken separately for the following: - a) Foundations, footings, bases of columns etc. and for mass concrete and precast shelves. b) Walls (any thickness) including attached pilasters, buttresses, plinth and string courses etc. , c) Suspended floors, roofs, landings, shelves and their supports and balconies. d) Lintels beams, girders bressummers and cantilevers. e) Columns, pillars, posts and struts.

f) Spiral (excluding landings) except Spiral Staircase. g) Spiral staircases (including landings). h) Arches. i) Domes, vaults, shell roofs, arch ribs and folded plates. j) Chimneys and shafts. k) Well steining. l) Vertical and horizontal fins individually or forming box, louvers and bands. m) Waffle or ribbed slabs. n) Edges of slabs and breaks in floors and walls (to be measured in running metres where below 200 mm in width or thickness).

o) Cornices and mouldings p) Small surfaces, such as cantilevers ends, brackets and ends of steps, caps and boxes to pilaster and columns and the like. q) Chullah hoods, weather shades, chhajjas, corbels etc. , including edges and

4. 2. 6. 4 Centring, and shuttering where exceeding 3. 5 metre height in one floor shall be measured and paid for separately. 4. 2. 6. 5. Where it is not specifically stated in the description of the item that form work shall be paid for separately, the rate of the RCC item shall be deemed to include the cost of form work. 4. 2. 6. 6 No deductions from the shuttering due to the openings/ obstructions shall be made if the area of such openings/obstructions does not exceed 0. 1 square metre. Nothing extra shall be paid forming such openings.

4. 2. 7 Rate The rate of the form work includes the cost of labour and materials required for all the operations described above.

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