Hollowcore Slabs

Hollowcore Slabs

One of the most advanced precast products. Millions of square meters of hollowcore slabs are used every year in the building constructions all over the world (villas, multistorey buildings, car parks, schools and shopping malls, etc.) where high quality control and safety standards are guaranteed at the Precast Plant.

Hollowcore slabs are used mainly for flooring and roofing, but can also be used for wall purposes.

Hollowcore slabs give the following advan-tages :a.) Lighter compared to equivalent cast in situ solid slab,thus material savings in design of all structural componentsb.) Provide excellent fire resistance and sound resistancec.) Smooth and excellent soffits for painting worksd.) Fast erection, thus savings in time and manpowere.) Designed according to ACI, PCI and CPCI international codesf.) Overall savings in Time, Labor, Shutter ing, Scaffolding & Building Materials

Bina standard slab types are 150mm, 200mm, 265mm, 320mm, 400mm and 500mm deep with 1200mm width

Openings

Holes in the Hollowcore slabs are made as indicated in the cross section drawing.Small holes are limited to the width of the voids. Small holes are usually made on the erection site. Big openings are made to the fresh concrete during production process.

Large Openings

The size of large openings depends on the span and the load required. Location of the holes are indicated in the drawing.

Large openings, which are larger than the slab are supported by steel headers.

Penetrations and block-outs in slab should not cut through the strand unless these have been allowed for in the design (Figure A). Any coring on site should be restricted to defined parts of members. Where large penetrations are required, full width head-ers (Figure B) may be used to support the end of a slab and transfer the load to the adjacent slabs. These slabs must be designed for the additional load.

PLAN FULL WIDTH OPENING

Figure (A) Penetrations Positions

Figure (B) Typical Header Arrangement

j = Center of Gravity of Strand Group The CG of the strand group relative to the top of the plank shall be within ± 6mm of the nominal strand group CG. The position of any individual strand shall be within ± 12mm of nominal vertical position and the ± 18mm of the nominal horizonta position and shall have a min cover 18mm.k = Position of Plates ……………….. ± 50mml = Tipping and Flushing of Plates ……. ± 6mmm = Local Smoothness …………. ± 6mm in 3m (does not apply to top deck surface left rough to receive a Plank weight) Plank Weight Excess concrete material in the plank internal features is within tolerance as long as the measured weight of the individual plank does not exceed 110% of the nominal published unit weight used in the load capacity calculation.n = Applications requiring close control of differential camber between adjacent members of the same design should be discussed in detail with the producer to determine applicable tolerances.

Transport and Erection

Clear access for delivery trucks and mobile crane is necessary for the erection of Hollowcore slabs. Erection procedure is executed in accord-ance with the design layout to ensure an uninterrupted continuous operation.Hollowcore slabs are placed directly on their places with shims for leveling and grouting purposes.

Hollowcore slabs are lifted with specially designed clamps hanging on a steel spreader.

As specified in ACI 318M-08 16.6.2.2-(a) Each member and its supporting system shall have design dimensions selected so that after consideration of tolerances, the distance from the edge of the support to the end of the precast member in the direction of the span is at least Ln/180 but not less than;

Cross Section Profiles Bearing Length

Fig. R16.6.2 - Bearing Length on SupportAC1318M - 08

Hollowcore Slab

Ln / 180 >/= 50mm ( slabs)

Ln /180 >/= 75mm ( beams)

bearing length

For Solid or Hollowcore Slabs.............. 50 mmFor Beams or Stemmed Members ....... 75 mm

Hollowcore Slab Load Table/ in excess slab weight (kN/m2)

The nominal Length of simply supported Hollowcore floor units is given in the table.