Formwork for beam and slab (column)

Formwork (shuttering) is the temporary mould into which wet concrete is poured and kept until it gains enough strength to support itself. It is made of timber, plywood, steel or aluminium.

Formwork for beam

• Beam bottom (soffit) plank: a 25-40 mm thick board, as wide as the beam, supported on head trees/props at 0.6-1.2 m spacing, standing on sole plates and wedges.
• Beam sides (cheeks): vertical boards fixed on both sides with cleats and struts at 0.6-0.9 m spacing, to hold the sides in place.
• The props are braced to each other horizontally and diagonally.

Formwork for slab

• Sheathing/decking: plywood or boards (18-25 mm).
• Joists (75 x 50 mm at 400-500 mm c/c) under the sheathing, supported on runners (ledgers) and props (vertical posts of steel or ballies) at 1-1.2 m, with a sole plate and wedges for easy removal.
• The edges are closed by a side form (stop board).

Formwork for column

• Sheathing: four side panels of boards (about 40 mm) or plywood (18 mm), stiffened by battens.
• Yokes/clamps: timber yokes or steel column clamps around the panels, placed closer at the bottom (where the concrete pressure is greatest) and wider apart at the top.
• Props: inclined props on two faces keep the column plumb; a cleaning hole is left at the foot.

 Beam & slab form (section)
   ___slab sheathing_________
   ___joists |  |  |  |  ___
        |cheek| beam |cheek|
        |     |soffit|     |
        |    head tree     |
        |      prop        |
        |_____ sole plate__|

Striking time (IS 456, OPC): vertical faces of beams, columns and walls 16-24 hours; slab soffits 3 days (props refixed); beam soffits 7 days (props refixed); props to slabs 7 days up to 4.5 m span and 14 days over 4.5 m; props to beams 14 days up to 6 m span and 21 days over 6 m. Surfaces should be oiled for easy removal.