Slip forming is a construction method for continuous concrete placing. Slip forming is normally applied for high structures like chimneys, silos, king posts, bridges, towers. This article features one case of using slip form for a clinker silo construction.
1. Objective
Objective of this procedure is to provide a guideline for sequence of operations pertaining to Slip form Works for Silo Construction, so as to ensure that the works are carried out in a systematic manner and to ensure that the works conform to the Owner’s specification and drawings.
2. Scope
This procedure is applicable for Construction of Clinker Silo.
3. Reference
This Procedure is based on the requirements of the Owner’s Technical Specification for Civil/Structural works for Silo package works and Simplex Experience in Construction of Silo by Slip form.
4. Resource Deployment
The Contractor shall deploy any or all of the following resources as dictated by the volume and nature of work.
a) Tools & tackles
Objective of this procedure is to provide a guideline for sequence of operations pertaining to Slip form Works for Silo Construction, so as to ensure that the works are carried out in a systematic manner and to ensure that the works conform to the Owner’s specification and drawings.
2. Scope
This procedure is applicable for Construction of Clinker Silo.
3. Reference
This Procedure is based on the requirements of the Owner’s Technical Specification for Civil/Structural works for Silo package works and Simplex Experience in Construction of Silo by Slip form.
4. Resource Deployment
The Contractor shall deploy any or all of the following resources as dictated by the volume and nature of work.
a) Tools & tackles
- Spade.
- Shovel
- Basket
- Wheel Barrow
- Steel Wire Rope
b) Plant & Machinery
- Batching Plant.
- Transit Mixer.
- Concrete Pump with pipeline.
- Builder Hoist Winch.
- Vibrator with nozzle.
- High lift curing pump.
- Boom Placer.
In addition to the above, the Contractor shall deploy a specialist agency for slip forming having experience for carrying out such work.
5. Slipform Technique:
We propose that we shall erect the slipform shuttering right from -2.0 m E.L. of R.C.C. Shell of Outer Wall. The shuttering plates and other various components of Interform type slipform equipment shall be erected as per line and level required for Clinker Silo.
The jack rod for 6.5 T Hydraulic Jacks shall rest on steel shoe placed at the top of already cast shell.
5.1 Yokes:
A set of yoke leg placed at required alignment and connected by means of yoke
beams at the top wherein climbing jack mounted, provides key members for fixing the Form Panel for inner and outer faces. Requirements of total number of yoke sets depend on the sizes of the structure and the capacity of hydraulic jack. Spacing of the jack would be around 2.0 m. for this Clinker Silo.
5.2 Slipform Hydraulic Jacks:
We shall be using 75 nos. 6.5 T capacities “Interform” type hydraulic jacks which climbs on bright steel rod of 32 mm dia and operates with two sets of ball grip. Jacks can only move upward direction when hydraulic pressure is applied. The upper movement of the slipform will be as per set criteria provided by the manufacturers of the Jacks or minimum of 100 mm / 150 mm per hour.
5.3 Consoles:
Consoles shall be provided on to the yokes meant for support of the working platform both inside and outside. This working platform shall be used for concreting, reinforcement binding and operation of the hydraulic pumps. Consoles will be fabricated members in combination with structural angles and tubular pipes/ reinforcement rod.
5.4 Hanging Scaffolding:
These members are suspended from consoles both inside and outside for the purpose of inspection and finishing work of the exposed concrete after slipping. These hanging scaffolds will be of rigid frame structural members.
5.5 Waler:
These member spans within the two yokes and provide support for the Form Panel against Lateral Force due to green concrete.
6. Support For Reinforcement Steel:
Arrangements made from the top of yoke beams with reinforcement guide, supports reinforcement to maintain its aligned position.
7. Guard Railings:
For the safety arrangement guard railings with post placed at the working platform both inside and outside and reinforcement type rails also provided for the hanging scaffolds.
8. High Pressure Hydraulic Pumps Pipelines & Fittings:
Circuit oil lines of high-pressure rubber hoses inter-connect all vertical jacks and plug in unit with one or more centrally positioned electrically powered high-pressure pump. Connections to the jacks and pump are carried out through valves and male and female fittings ‘as required’.
9. Illumination:
Illumination is essentially required as the work normally carried out 24 hours a day nonstop. Accordingly both on working platform, at the hanging scaffolds, stairways and working areas are illuminated properly.
10. Operation:
For smooth operation of slipform, jack readings and plumb readings are to be monitored once in every two hours.
11. Access Tower:
Tubular access tower is to be installed for concrete lifting and climbing of personnel through temporary stairs, made of reinforcement rod and fixed with tower.
12. Special Arrangements:
1. Minimum 10% extra jacks are required as standby. Adequate jack rods should also be available at site.
2. 75 nos jack of 6.5T capacity each to be put on the job i.e. with a spacing of around 2m c/c.
3. Slow and uniform concrete pouring is to be maintained. Empty height of shutters should be maintained 150-200mm from top/ deck level. Lifting of the shutters should be limited to 10mm –15mm per lift i.e. in 10minutes interval, (60-90 mm per hour) to avoid bulging of concrete surfaces, rate of slippages will also depend on the concrete quality (i.e. on setting time)
4. To maintain verticality of shell wall, 12 nos plumb bobs (minimum) are to be hanged at equal intervals at outer side of shell wall from deck through the gap between shutter and masons’ platform (hanging platform), however the plumb points should be avoided in front of openings. Verticality shall be checked at least 2 times in every shift jointly. On the entire jack rod horizontal level is to be marked at 300mm height from top of the jack by means of water level tube and Jack rod rings are to be put at this level on the entire jack rod. During lifting when the entire jack touches the ring then horizontality of the system will be ensured. At this time dia & plumb checking will be done and readings are to be noted in a register. If any discrepancy is found that is to be brought to the knowledge of the Owner’s Site In-charge immediately for necessary remedial measures. Same procedure will continue till successful completion of slip form concreting of shell wall.
5. All axis to be marked on the deck slab by means of triangular shaped GI sheet /Ply.
6. One standby hydraulic pump of same capacity in OK condition must the there on the deck slab.
7. Curvature of the walers should be proper to get accurate inner & outer diameter of the shell wall when shutters are fixed in position. Curvature of all walers must be checked before fixing.
8. It should be ensure that the quality of concrete as is required for slip forming work and the desired speed as recommended for slip form work is achieved. The quality of construction of the silo is ensured and the silo is executed within permissible tolerances.
9. Concreting & other related job shall be continued round the clock till completion of slip form.
10. Continuous /intermittent curing shall be done by means of high lift pumps and perforated Circular water pipe line fixed 500mm above masons’ platform both inner and outer side of silo wall.
11. Simultaneous finishing of concrete surfaces shall be done by masons working at mason’s platform.
12. For the jack rods, in opening portions, dummy concrete columns are to be made, which are to be dismantled later on after completion of the job.
5. Slipform Technique:
We propose that we shall erect the slipform shuttering right from -2.0 m E.L. of R.C.C. Shell of Outer Wall. The shuttering plates and other various components of Interform type slipform equipment shall be erected as per line and level required for Clinker Silo.
The jack rod for 6.5 T Hydraulic Jacks shall rest on steel shoe placed at the top of already cast shell.
5.1 Yokes:
A set of yoke leg placed at required alignment and connected by means of yoke
beams at the top wherein climbing jack mounted, provides key members for fixing the Form Panel for inner and outer faces. Requirements of total number of yoke sets depend on the sizes of the structure and the capacity of hydraulic jack. Spacing of the jack would be around 2.0 m. for this Clinker Silo.
5.2 Slipform Hydraulic Jacks:
We shall be using 75 nos. 6.5 T capacities “Interform” type hydraulic jacks which climbs on bright steel rod of 32 mm dia and operates with two sets of ball grip. Jacks can only move upward direction when hydraulic pressure is applied. The upper movement of the slipform will be as per set criteria provided by the manufacturers of the Jacks or minimum of 100 mm / 150 mm per hour.
5.3 Consoles:
Consoles shall be provided on to the yokes meant for support of the working platform both inside and outside. This working platform shall be used for concreting, reinforcement binding and operation of the hydraulic pumps. Consoles will be fabricated members in combination with structural angles and tubular pipes/ reinforcement rod.
5.4 Hanging Scaffolding:
These members are suspended from consoles both inside and outside for the purpose of inspection and finishing work of the exposed concrete after slipping. These hanging scaffolds will be of rigid frame structural members.
5.5 Waler:
These member spans within the two yokes and provide support for the Form Panel against Lateral Force due to green concrete.
6. Support For Reinforcement Steel:
Arrangements made from the top of yoke beams with reinforcement guide, supports reinforcement to maintain its aligned position.
7. Guard Railings:
For the safety arrangement guard railings with post placed at the working platform both inside and outside and reinforcement type rails also provided for the hanging scaffolds.
8. High Pressure Hydraulic Pumps Pipelines & Fittings:
Circuit oil lines of high-pressure rubber hoses inter-connect all vertical jacks and plug in unit with one or more centrally positioned electrically powered high-pressure pump. Connections to the jacks and pump are carried out through valves and male and female fittings ‘as required’.
9. Illumination:
Illumination is essentially required as the work normally carried out 24 hours a day nonstop. Accordingly both on working platform, at the hanging scaffolds, stairways and working areas are illuminated properly.
10. Operation:
For smooth operation of slipform, jack readings and plumb readings are to be monitored once in every two hours.
11. Access Tower:
Tubular access tower is to be installed for concrete lifting and climbing of personnel through temporary stairs, made of reinforcement rod and fixed with tower.
12. Special Arrangements:
1. Minimum 10% extra jacks are required as standby. Adequate jack rods should also be available at site.
2. 75 nos jack of 6.5T capacity each to be put on the job i.e. with a spacing of around 2m c/c.
3. Slow and uniform concrete pouring is to be maintained. Empty height of shutters should be maintained 150-200mm from top/ deck level. Lifting of the shutters should be limited to 10mm –15mm per lift i.e. in 10minutes interval, (60-90 mm per hour) to avoid bulging of concrete surfaces, rate of slippages will also depend on the concrete quality (i.e. on setting time)
4. To maintain verticality of shell wall, 12 nos plumb bobs (minimum) are to be hanged at equal intervals at outer side of shell wall from deck through the gap between shutter and masons’ platform (hanging platform), however the plumb points should be avoided in front of openings. Verticality shall be checked at least 2 times in every shift jointly. On the entire jack rod horizontal level is to be marked at 300mm height from top of the jack by means of water level tube and Jack rod rings are to be put at this level on the entire jack rod. During lifting when the entire jack touches the ring then horizontality of the system will be ensured. At this time dia & plumb checking will be done and readings are to be noted in a register. If any discrepancy is found that is to be brought to the knowledge of the Owner’s Site In-charge immediately for necessary remedial measures. Same procedure will continue till successful completion of slip form concreting of shell wall.
5. All axis to be marked on the deck slab by means of triangular shaped GI sheet /Ply.
6. One standby hydraulic pump of same capacity in OK condition must the there on the deck slab.
7. Curvature of the walers should be proper to get accurate inner & outer diameter of the shell wall when shutters are fixed in position. Curvature of all walers must be checked before fixing.
8. It should be ensure that the quality of concrete as is required for slip forming work and the desired speed as recommended for slip form work is achieved. The quality of construction of the silo is ensured and the silo is executed within permissible tolerances.
9. Concreting & other related job shall be continued round the clock till completion of slip form.
10. Continuous /intermittent curing shall be done by means of high lift pumps and perforated Circular water pipe line fixed 500mm above masons’ platform both inner and outer side of silo wall.
11. Simultaneous finishing of concrete surfaces shall be done by masons working at mason’s platform.
12. For the jack rods, in opening portions, dummy concrete columns are to be made, which are to be dismantled later on after completion of the job.
13. Spokes will be placed at the middle portion of two consecutive yokes alternatively.
14. Proper illumination should be there at top of deck as well as at mason’s platform. Area lighting inside/outside also should be proper as during nighttime also plumb readings to be checked.
15. After completion of slip form activity the Jack rods are to be recovered and the holes are to be grouted as per mix specified in contract/ as decided by Engineer in charge.
14. Proper illumination should be there at top of deck as well as at mason’s platform. Area lighting inside/outside also should be proper as during nighttime also plumb readings to be checked.
15. After completion of slip form activity the Jack rods are to be recovered and the holes are to be grouted as per mix specified in contract/ as decided by Engineer in charge.
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