This precast floor system comprises prestressed planks spanningbetween load-bearing walls. Where voids, stairs and other features prevent the slabs from spanning between walls, slabs spanning perpendicularly are provided, supported by the adjacent planks.The merits of this system are as follows:• Floor beams are eliminated, resulting in simpler components and reduced services coordination problems.• Stepping of building line at front and rear are easily accommodated.• Full height window and other facade features can be designed• Can accommodate irregular layouts, with less requirement for false ceilingsIn this system, the following factors need to be considered:• At roof level, any significant RC gutters will prevent slabs from spanning between walls.• For some floor layouts, alignment of stair openings and voids can prevent slabs from spanning between walls.• The volume of concrete for this system is likely to be 0 ~ 20% higher than conventional RC beam and slab.

A cast-in-place concrete system is constructed by pouring concrete in forms at site . this system utilizes one way and two wayThe advantages and dis advantages of this system compared to precast are as follows

monolithic construction post tensioning compressive force reduces cracking in slabs. Perception of higher ceiling and more openness. Lower maintenance cost Construction can be performed by local sub contractorsusing local labour.

Whilst it is possible to adopt precast construction at first storey, it is consideredunlikely that this will be cost effective or provide significant buildability advantagesover conventional beam and slab for first storey construction. This is based on the

considerations that the formwork cost for construction on grade is negligible, and theextent of in-ground services will, in general, be substantial.Adopting conventional construction for the first storey has the additional advantage ofproviding more lead time for the production of the precast components. However, it isalso possible and sometimes advantageous to use a precast system for the groundbeams and slab.

Precast, pre-stressed concrete beams are widely used in construction projects where speed and ease of erection are important. A number of different bridge beam sections are available, reflecting the range of applications for which they are intended.

1. set reference line and offset line to determine the position of the precast elements to be installed.

Level th precast beam elements during installation.

Put up temporary props to support the precast beam elements

2provede level pads or shim plates for setting the level of the elements . set the level pads in position using non-ink mortar

3. for precast external wall/column ,fix the compressible form or backed rod on the outer perimeters of wall

4. lift and rid the panel to its designed location with the use of wire ropes.

5. adjust the panel to position and secure it with diagonal props.

6. for components with cast in-situ joints , place and lap the rebars as required.,

7. Set up the formwork for the casting of the joints

8. Carry out conctrete casting.

9. Remove forms after sufficient concrete strength has been achived.

Construction within a precast yard generally yields improved quality and higher rates of production since materials, equipment and staff are all close by, and the work tends to be highly repetitive. The precast yard can be either:

• A precast supplier’s yard, in which case it is a permanent facility; or

• A temporary precast yard established on site, where all materials and equipment are close at hand.

By its very nature, precast yards can produce components at a very rapid rate. For example, several precast parapets can be cast each day. Quality control is therefore very important. The precast yard

operator must have a quality system in place whereby each stage of the operation is inspected by the operator and signed off before moving to the next stage.