Timber and concrete upper floors

6.4

6.4.7Precast concrete

Precast concrete upper floors shall be erected in accordance with the design.

Precast concrete flooring systems should be in accordance with BS EN 1992-1-1 or Technical Requirement R3.

For precast concrete systems:

  • details of manufacturer’s assembly instructions and any independent certification should be available on site and followed
  • beams, planks or infill blocks that are damaged should not be used
  • adequate support should be provided until design strength is reached
  • joints should be grouted in accordance with the manufacturer’s recommendations.

Bearings should be:

  • solid and level
  • 90mm minimum on masonry (open frogs in brickwork should be filled)
  • 75mm minimum on steelwork.

The setting out of beam and block floors should:

  • ensure correct spacing between beams, using infill blocks as spacers
  • be in accordance with the design
  • allow for additional beams where required to support concentrated loads such as partitions.

Infill blocks should:

  • be omitted or cut where necessary to allow for services
  • be cut carefully and neatly without damage (not using a hammer and bolster).

Where floors rely on structural topping or in-situ make-up sections, propping may be needed until the in-situ concrete has reached design strength.

Trimmed openings

Where voids in precast concrete floors are to be trimmed:

  • specifications and drawings should be followed
  • steel trimmer shoes may be used.

Double beams, common around trimmed openings, should be adequately supported until all voids have been solidly concreted and the concrete has reached its design strength.

Restraint straps and ties

Straps:

  • should be shown in the design
  • are generally required where beams run parallel with the wall