Information for the Designer

Slipform Notes A

  1. Depending on the plan shape and the re-usability of the shuttering, the economy of the slipform system begins at a height of 5 m.
  2. The wall thickness should amount to at least 12 cm. Rectangular or acute-angled corners of the building are bevelled.
  3. The concrete base for assembly of the slipform system must be horizontal. The reinforcing rods should project into the rising concrete by more than the customary transfer length, due to the fact that the concrete strength is still low when sliding commences.
  4. The same grade of reinforcing steel should be used wherever possible and spaced at uniform intervals. If small amounts of reinforcing rods are involved, it is better to reduce their diameter than increase the intervals between them.
  5. The projecting reinforcing .rods of the floors are bent sideways and horizontally into the slipform system. They must therefore be of Grade I reinforcing steel (tensile strength 48,348 - 71,100 psi) and feature a diameter of not more than 12 mm. The projecting re¬inforcements for the final floor must not obstruct the shuttering when the latter is slid clear of the concrete.
  6. The normal length of the vertical reinforcements should not exceed the following maxi¬mum values for the different round reinforcing rod diameters: 8 mm dia. - 3.00 m; 10 mm dia. - 3.50 m; 14 mm dia. - 4.00 m; 16 mm dia. - 5.00 m; 18 mm dia. and above - 6.00 m. The lengths are staggered for the bottom layer and uniform for the other layers. The intervals between the vertical reinforcements are adapted to the respective wall thickness, but must never exceed 40 cm. In the case of thin walls, they should be two times of the wall thickness at the maximum. In the case of reinforcement on one side only, stirrups must be provided at minimum intervals of 50 cm in the jacking rod zone, in order to prevent buck¬ling of these rods.
  7. Depending on the concreting lift, the interval of the horizontal reinforcements should be 20 cm or 25 cm or a corresponding fractional amount hereof.
  8. The overall number of reinforcements and their intervals should be selected to obtain as closely-knit and as strong a mesh as possible. A strong mesh helps to prevent patches of concrete from being torn off due to friction between the concrete and the shuttering.
  9. In order to facilitate placing of the covering concrete, the horizontal rods should be positioned as far on the outside as possible.
  10. The concreting stages and the site facilities should be selected so as to guarantee a placing rate of at least 15 cm per hour.
  11. The use of round gravel with a maximum grain diameter of 30 mm prevents the shuttering from tearing off individual particles or patches of concrete, thus disturbing the exposed surface of the concrete or its structure. If possible, manufactured sand should not be used.
  12. The concrete should be homogeneous throughout and "easy to work"; its granulometric composition, consistency and cement content correspond roughly to those of exposed concrete or watertight concrete. The W/C ratio should lie between 0.55 and 0.70 (0.60 is preferable). This corresponds to a plastic concrete which does not segregate during pouring. Omitted-size grain mixes have proved satisfactory here. Depending on the top size of aggregate and cement content, a certain quantity of 0-0.2 mm grain (siliceous dust, trass or the like) must be added. The correct batching, mixing and placing of the concrete is the task of the general contractor, for which we do not assume any responsibility whatsoever.
  13. Standard cements of known origin and qualities should be used wherever possible. When necessary, the pouring rate must be coordinated with the setting rate of the cement. The use of Portland cement 275 is normally recommended, while Portland cement 375 is advis¬able during cold weather as well as for tall structures and high pouring speeds.