There is no doubt that during the lifetime of a structure the requirements of a tenant may alter with time or the tenant may change several times. Each new tenant will have his own requirements for mechanical, hydraulic, and electrical services, as well as loading arrangements and general layout. Therefore, for a building to remain readily, it must have the flexibility to accommodate openings for stairs, services or lifts, and the possibility for changes in loading patterns.
Holes through pre-stressed slabs can be accommodated easily if they are identified at the design stage. Small holes (less than 300 mm x 300 mm) can generally be positioned anywhere on the slab, between tendons, without any special requirements. Larger holes are accommodated by locally displacing the continuous tendons around the hole.
It is good detailing practice to overlap any stopped off (or ‘dead-ended’) tendons towards the corners of the holes in order to eliminate any cracking at the corners In ribbed slabs, holes can be readily incorporated between ribs or, for larger holes, by amending rib spacing or by stopping-off ribs and transferring forces to the adjoining ribs.