The execution of slipform job requires a complete and detailed preparation as many simultaneous and successive operations are involved. The method of construction, preparation of scheme drawings, calculating the requirement of slipform materials, equipment’s, tools & tackles, consumable, manpower etc needs thorough planning.

It also involves mix design, admixtures to be added for the concrete, reinforcement around openings and planning for other related works on the slip formed structure.

On large site with several structures built with the same slipform, planning includes

• Work below slipform level
• Detailed programme for the wall
• Work involved in intermediate floors, if any.
• Embedment/pockets and other installations during slipform

The number of yokes for each silo is calculated based on the diameter of the silo. The yoke to yoke distance is normally kept between 1.25 and 1.35 m.Once the number of yokes required is calculated the list of materials can be prepared from the master list. The requirement of jack rods depends on the height of the structure. Always keep 5% extra material as spare.

The length of yoke beams = Wall thickness + 1000 mm.

Normally 2 Nos. Yoke beams at the bottom and 1 at the top are fixed. Wherever yokes are used for supporting some lifting arrangements, there the top yoke beams also shall be 2 no back to back.

The capacity of Jacks to be deployed depends on the following loads:

Deadweight of yokes,

Deadweight of Concrete lifting arrangements

Weight of Platform with 40 thk plank

Weight of wooden Runners 125 X 75mm

Total Dead Load = X

Live load over platform @ 200kg/sqm

Weight of Concrete 0.5 cum

Weight of Steel (reinforcement, jack rod stacked on the platform)

Total Live load – Y

Frictional forces @0.173kg/m (length along the wall sides) – Z

Total Load on Slipform, L = (X+Y+Z) * t

Required Jacking Capacity (W) should be with 1.4 factor

Note:- Jack shall not be loaded more than 80% of its capacity.

The quantity of concrete required per meter height should be calculated first. The slipping speed can be assumed based on the quantity of concrete, reinforcement, pre-stressing and other related items. Rate of rising depends on the above and setting time of concrete. Once the slipping speed is assumed the concrete requirement per shift can be calculated. Once the quantity per shift is known, with 25% spare capacity, the size and number of mixing and lifting equipment shall be decided.

The standard list of consumable is given along with the master material list. The number of electrodes, gas, grease, oil etc. can be given approximately. The wire rope required for hoisting to be calculated separately based on the height of the structure.

The requirement of timber is for the following areas.

1.Working platform

2. Mason’s platform

3.Runners for supports

4.Planks for the bracket platform if the assembly is taken up from higher elevation

Timber platform consisting of four parts

a) Supporting runners 5”x 3”x 7’ long & 6’ long

b) Wooden planks 6” x 1½” x 6’ long.

c) Toeboard size: 4” x 1½” x 6’ long

The requirement of labour for various activities can be calculated based on the productivity norms, site conditions and type of structure. It is preferable to engage one single agency for the entire slipform works in a project to have better control over productivity and also optimum use of workmen with multi-skill.

I hope you find this information useful. If there is something that I have missed or I do not know, you can comment and tell me which I will try to rectify as soon as possible.

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