This post provides a quick overview about construction of service cores of tall buildings using slipform construction technique.
Slipform construction technique has been gaining a lot of popularity over the years in the construction of mid to high-rise buildings because of the many advantages it has to offer, especially for buildings having about ten storeys or more. For low-rises however, this approach is economically not viable. In previous posts, use of this technique for other tall structures like chimneys, silos, cooling towers etc. was briefly discussed. In case of these structures a non-stop concrete pouring schedule is normally adopted in order to impart monolithic attributes to the structures by keeping joints, voids, discontinuities etc. in the structures to the bare minimum. The same is however not a basic necessity for buildings and hence around the clock concreting too is not a must in the case of slipform construction method for highrises. A day-time-only kind of construction schedule is not uncommon in such projects. Nevertheless, if situation permits, an around-the-clock schedule would always result not only in higher progress but also in higher economy. Quality of the product is also quite superior.
There are several reasons of slipform construction being economical for tall buildings or structures. The key reason is the repetitive nature of the method itself. Once installed, the formwork need not be dismantled and reinstalled again for further use. The same setting continues till the job, in this case the core structure of a high-rise, is complete. Even in the case of a very tall building where the core is sometimes reduced abruptly at certain elevations for various reasons, change in settings of the slipform structure need to be done only at those few particular elevations. This results in saving a great deal of time, manpower as well as materials and thus becomes more economic than conventional methods. The method of construction requires a much smaller group of highly skilled workers as compared to other usual methods including jump-form method. It also needs lesser quantity of forms.
Slipform construction technique is normally adopted for the centrally located service core of a highrise. The service core or simply core of a high-rise building is normally located at the central portion of the building which hosts facilities not meant for dwelling or renting purposes but for common uses of all the occupants or users of the building and are integral parts of any such building. These include the elevator shafts, public restrooms or toilets, ventillation & electrical shafts, stairwells etc.
The foundation of the building core along with starter walls of height 1.5m to 2m are constructed precisely as per drawings to start with. The starter walls, meant for commencing installation of slipforms, must have all the necessary embedments/provisions including the jack-rods on which the entire slipform unit would climb up. The walls also must have all the vertical reinforcing steel bars with adequate projections.
Contd. in Part-II….