Precast Hollowcore & solid floors

Bearings can be taken from brickwork, blockwork, steel beam flanges or shelf angles and concrete. Longitudinal joints: the sides of the slabs are cast with a shear key profile which when filled with C25/30 grade concrete distributes loads to adjacent units.

The nominal bearing for: Masonry: 100mm Steel: 75mm Concrete: 75mm

Slabs are usually manufactured to have 100mm bearing onto a 100mm wide wall. However, where slabs share an intermediate wall, the wall must have a minimum thickness of 190mm.

To provide effective lateral restraint, slabs are built into parallel spanning walls with a continuous bed of mortar between slab and wall. This not only seals the joint but ensures wall loads are transferred through the slab.

Where high wall line loads are present, the outer core can be filled solid to further enhance load transfer capacity of the slab.

For walls narrower than 190mm, slabs must be tied together to allow for construction and manufacturing tolerances. Typically, two cores per 1200mm-wide slab are formed open so that a reinforcement bar can be inserted across the slabs.

The cores are then filled in-situ with concrete to form the tie detail. The cores on opposing slabs must line up to facilitate this detail.

Slabs can be formed with either reduced ends or a notched end to allow the slab to sit on the shelf angle.

The void between the unit and the steel beam is then filled with C25/30 grade concrete by the main contractor to tie the components together. The nominal bearing length is 75mm on steel work.

To provide lateral restraint to the steel beam and to meet sound/fire requirements, it is necessary to fill the void between the hollowcore unit and the steel beam with C25/30 grade concrete.

Standard units can be provided for class 1 and 2A buildings with a nominal bearing of 75mm.

Where the nominal bearing is less than 75mm, the same detail as used for masonry walls less than 190mm is required.

Should continuity be required, then the same detail as for masonry walls less than 190mm can be used. Note that the cores on opposing slabs need to line up to facilitate this detail.

To comply with ‘disproportionate collapse requirement’, open cores can be provided to allow the slabs to be tied to shear studs. This requires close co-operation to ensure that the setting out of the cores and shear studs align.

To accommodate service voids and column notches, the hollowcore can be pre-formed to individual requirements. Large openings may require steel trimming supports. It is recommended that holes of less than 100mm diameter are drilled on site, on the centreline of cores.

A number of ceiling finishing options are suitable for hollowcore units: soffits can be plastered using a suitable bonding agent. Proprietary suspended ceiling systems can be hung from supports located between units. Counter battens can be screw-fixed to the soffit for a plasterboard finish.

Bison Precast is able to offer several solutions to incorporate balconies within a floor layout: additional reinforcement can be incorporated into hollowcore slabs to accept bolt-on steel balconies. 100mm-thick solid prestressed slabs can be used as permanent formwork for a cast in-situ balcony. We have 150mm-thick solid prestressed slabs that incorporate top reinforcement to form the balcony and backspan slab as a single unit. Alternatively we can supply RC units cast with integrated thermal breaks.

Where hollowcore or solid flooring units bear onto structural steel work, significant economies can be achieved by designing the steel beam to act compositely with the precast units. This enables the possibility of a reduction in composite steel beam sizes and section weights of the steel frame, and the overall supporting structure. Shear studs are welded onto the top flange of the steel beams and reinforced in-situ concrete enable the precast and the steel work to act in unison. Composite steel beam design technical guidance – download here

Our precast hollowcore composite combines hollowcore slab with a composite structural concrete topping. Ideal for applications where enhanced structural performance and lateral load distribution is required, such as in industrial buildings, and multi-storey buildings and car parks.

Our solid composite floors combine solid prestressed units with a composite structural concrete topping that is applied after the solid slabs have been installed. Solid prestressed units are manufactured in 100mm depths and are suitable for many commercial applications.