One way slab One way Ribbed Slab(Joist Slab) Two way Slab Two way Waffle Slab (Grid) Two Way Flat Slab
In Situ Cast Reinforced Concrete Slabs Reinforced concrete floors have a better resistance to damage by fire and can safely support greater superimposed loads than timber floors of similar depth. The types of reinforced concrete slabs that are used for buildings are monolithic in situ cast slabs, waffled grid slabs, self-centering “T” beams and infill blocks, hollow beams and.
The word centering is used to describe the temporary platform on which in situ cast concrete floors are constructed and supported until the concrete has sufficient strength to be self supporting.The term self- centering is used to define those precast concrete floor systems that require no temporary support.
Monolithic Reinforced Concrete Slabs The word monolithic is used to describe one unbroken mass of any material. A monolithic reinforced concrete floor is one unbroken solid mass between 100 and 300 mm thick, of in situ cast concrete, reinforced with mild steel reinforcing bars. To support the concrete while it is still wet and plastic, and for 7 days after it has been placed, temporary centering has to be used. This takes the form of rough timber boarding, plywood, block board or steel sheets, supported on timber or steel beams and post.
The steel reinforcement is laid out on top of the centering and raised 20 mm or more above the centering by means of small blocks of fine concrete which are tied to the reinforcing bars with wire or by plastic spacers. The wet concrete is then placed and spread on the centering and it is compacted and levelled of.
Waffle Grid Slabs If the column grid is increased from about 6.0 about 12.0 square or near square it becomes economical to use a floor with intermediate cross beams supporting thin floor slabs. The intermediate cross beams are cast on a regular square grid that gives the underside of the floor the appearance of a waffle, hence the name.
The advantage of the intermediate beams of the waffle is that they support a thin floor slab and so reduce the dead weight of the floor as compared to a flush slab of a similar span. The economic span of floor slabs between intermediate beams lies between 900 and 3.5. The waffle grid form of the floor may be cast around plastic or metal formers laid on timber centering.
Reinforced Concrete and Clay Block Slabs The particular advantage of this type of floor is its good resistance to damage by fire. To keep the death weight of the floor as low as possible, compatible with strength, it is constructed on in situ reinforced concrete beams with hollow terra cotta infilling blocks cast in between the beams. The words terra cotta mean “earth burnt”.
This type of floor has to be given temporary support with timber or steel centering. The terra cotta blocks and the reinforcement are set out on the centering and the pieces of clay tile are placed underneath the reinforcing bars. Concrete is then placed and compacted between the terra cotta blocks and spread 50 mm thick over the top of the block.
Precast “T” Beam and Infill Block Slabs This type of reinforced concrete floor is much used for comparatively small spans and loads. The great advantage of this floor system is that, the small units can be handled by two men without the need for lifting gear. Solid reinforced concrete beams usually shaped like an inverted T in section are precast in manufacturer’s yard to the required length. The depth of the beams is from 130 to 250 mm and 20 mm wide at the bottom. The beams are made in lengths of up to 6 meter.
The “T” beams are reinforced with mild steel reinforcing bars. Hollow precast light weight concrete infill blocks are made to fit between and bear on the “T” beams. These blocks are hollow and made for lightness in handling and to minimize the weight of the floor. The blocks are placed in position and floor completed with a layer of constructional concrete toping, 50 mm thick spread and levelled ready for a screed. The under side or soft feet of the floor is covered with plaster or will provide support for a suspended ceiling.
Hollow Beam Slab Units Hollow, reinforced concrete beams are precast around inflatable formers to produce the hollow cross section. The beams are rectangular in section with the steel reinforcement cast in the lower angles of the beam. The sides of the beams are indented to provide a key for the concrete toping.