IS 10505-1983 covers the detailed standard specifications, dimensions, sampling procedure and testing methods. It contains 15 sub divisions. They are
It gives the details about the content of the standard.
- Shape and Size:
The prefabricated elements are in the shape of square, round, rectangle, triangle or any other shape. The outer surface of the elements having outward slope is allowed. Hence the maximum inclination 3º is essential. Remove the element from the mould. Size of units, depth and lateral dimensions of the units shall be as per structural design and it will vary according to the loads and spans. The minimum thickness of the flange and wed of the element should be 25mm.
The materials used in the prefabricated structure should confirm to IS 456-1978.
- Structural design:
Load acting on the element should be analyzed by using any one method of analysis. The pre cast units have adequate strength during the following stages 1.Demoulding, 2.Handling.
- Transporting and placing:
The factor of safety should be minimum of 1.5 taken to account for finding design load.
The mould used in the PFB manufacturing should consist of at least two parts. The mould can be made up of timber, steel, concrete, FRB, plastics or any other materials acceptable to engineer in charge. When using concrete or masonry moulds, its surfaces should be finished to the required accuracy.
- Reinforcement in pre cast unit:
Reinforcements should be provided according to the structural requirement. Any mesh type or welded bar type reinforcement should be placed within the mould with the minimum spacing of 100mm from either side.
The concrete used in PFB should be minimum grade of M20.
- Casting and curing:
Mechanical vibration of mould or table is essential to ensure the proper completion. Needle vibrations are used on the important surfaces of the element. Curing must be done in accordance with IS 456-1978.If necessary strain curing may be provided to get the early stripping.
Tolerance of ±5mm for length and breadth, ±2mm for thickness of precast. Dimensional variations can be accepted.
- Sampling and testing:
Sampling size taken for testing is based on the production lot size. For a lot size of 100 the number of samples tested is 5. For a lot size 101-300 samples of 8 must be tested. Load tests of floor and roof must be carried out in accordance with IS 456-1978.
- Transportation and erections:
Lifting hooks are provided during casting to facilitate demoulding, loading, unloading and erection period. After erection, the hooks can be either cut or bent down inside the element. For transporting and placing, the ropes should be tied near the ends 1/5th of the length from either end. In case of units are transported in trolleys, the overhanging of units from the trolley should not be more than the 1/5th of length. The units placed must be started from one end of the building.
- Curing of joints:
The joints of the PFB units should be cured for a minimum period of 7 days in accordance with IS 456-1978. The load of the cement slurry can be applied to the joints to seal the gap.
Designers should give the provisions for fixtures like fan hooks, electrical members, plumbing work etc. If necessary, separate conduits may be placed within the PFB unit. Holes, openings required are to be provided within the precast unit. Avoiding drilling of holes, cutting of edges is necessary unless permitted by engineer in charge.
- Floor finish:
In case of floor slab, the floor finish must be done accordance with related indian standard IS 10505-1983. The floor thickness at any place should not be less than 75mm.
- Roof treatment:
Adequate water proofing and thermal insulation to suit the local climatic condition must be ensured. The roof/floor span length 6m having ribs width not less than 100mm, spaced at a distance of 750mm apart. If the roof/floor span length is more than 6m, minimum rib of width not less than 150mm must be provided and spaced at a distance of 500mm.