SLIP FORMWORK

GUIDED BYProf. VRK MURTHY

SUBMITTED BYVikas B. More (73036)

Aniruddha S. Namojwar(73038)

Definition

The slip form process can be defined as an execution process for the construction of such reinforced concrete structures which are exceptionally high. It involves operations of highly sophisticated nature and round the clock concreting work.

The slip form primarily consists of shuttering panels which envelop the structure along its designed shape and then are moved upwards continuously leaving below the structure in its final form.

Advantages of Slip form• Reduction in construction time period.• An average progress of 3.0 to 4.0 m height per day

can be easily achieved with slip form.• The construction joints get eliminated as the slip

form process is a round the clock process.• The surface finish of the concrete is of very high

order.• Full dimensional i.e. shape, size etc,. is achieved in

slip form work.

Area Of ApplicationIt is best suitable for:• Vertical and tapered chimneys• Walls and columns of greater heights• Silos• Cooling towers• Square or rectangular buildings with uniform plan for

the full height to be slip formed.• Bridge piers• Water tanks• Storage bins• Any other shaft type buildings

Components of Slip form

• Shuttering/Form panels• Walers• Yokes• Working Decks• Hanging Scaffolds• Lifting equipments i.e. jacks and jack rods• Other miscellaneous equipments.

Outside yoke leg main

yoke

Distance bar

Outside hanging scaffold

Beam for bracing of main yoke

Outside yoke leg with U

normal

• Shuttering Form panels of MS plates 8mm thick and size 1m x 2m

are normally used.Use of timber, particle board or plastic form panels are

avoided due to a higher frictional drag.The shuttering should be able to carry the loads coming

on it during vibration of concrete, sliding or erection for which steel form panels prove better.

All the laps and joints in the shuttering should be vertical. Inclined joints or overlaps may cause a drag component in horizontal direction which will cause torsional effects on slip form assembly.

• Walers Stiffen the slip form panels and carry the loads to the

yokes. Made strong enough to take the lateral pressure of the

fresh concrete laid inside the form panels.The walers transfer the weight of form panels, the

loads from hanging scaffolds and working decks to the yokes.

The walers may be made of timber or steel.If the yoke – panel is more than 3.0m in span, the

walers are to be braced suitably.

• YokesConsist of yoke legs and yoke beamsAll the loads from working deck, hanging scaffolds,

form panels and the concrete pressure get transferred to the jacks through yokes only.

A yoke consists of one outer yoke leg, one inner yoke leg, essentially one yoke beam on which the jack is installed and mostly another yoke beam.

• Working decksThe working decks are required for complete operation

of slip form equipment and bringing up all type of materials, equipment, concrete, staff and workers.

Deck is provided to bring in concrete, reinforcement steel and other required materials.

An additional working deck is provided for the work of tying of reinforcement steel, compaction of concrete and operation of slip form.

The working decks are made of steel components placed at suitable spacing covered with timber planking.

The number of main trusses and spider beam may vary depending upon the number of yokes to be used which further depends upon the diameter of the structure. The sliding working deck is also to carry loads to carry due to movement of staff, vibrators for compaction of concrete and operation of slip form equipment.To bear the service loads, the steel components of top deck should preferably be of structural steel.

• Hanging ScaffoldsInner and outer hanging scaffolds, either both or any of

the two, as the structure demands, are provided to finish the concrete surfaces.

Hanging scaffolds normally consists of steel stirrups suspended from the yokes and horizontal space between stirrups is covered with timber planks.

The hanging scaffolds run along the entire area below the working decks. The maximum distance of the hanging scaffold from the wall should be limited to 200mm.

• Lifting equipmentsjacking system.lifts the slip form equipment assembly as a whole

including all the structural frame work, yokes, walers, hanging scaffolds, all the decks, all the live loads and service loads.

It comprises of three components:• Jacks• Jack rods or pipes• Pumping station in case of hydraulically operated

jacks.

• Other Miscellaneous EquipmentsBracingsScrews: Radius and wall thickness screwsStretching screws Safety netsExtraction jacksGrouting pumpThe number of items required for a complete slip form

assembly may vary for different type of structures with respect to their structural and dimensional requirements.

Erection of slipform EquipmentThe erection of slip form equipment and ancillaries

should be followed as per the documents given by the slip form supplier.

The operation of the slip form, the accuracy of the parameters and the quality of the slip formed structure depends upon the exactness in erection of slip form equipment.

Sequence of erection in general:• Marking layout on ground level, Erection of

temporary staging, laying truss members and spider beams, connect all truss members and spider beams with bolt connections.

• Bring the truss in the true level by checking it in a water level and by adjusting the temporary staging supports below the truss.

• Mark the position of yokes. . Fix inner and outer yoke legs at the marked positions. Complete the yokes by fixing yoke beams to yoke legs. So each spider beam has now been provided with a yoke.

• Fixing shuttering form panels. For tapered structures form panels will overlap. Fix wall thickness screws and radius screws to all the yokes.

• Fix hanging frame for hydraulic pump to the working deck, place the hydraulic pump in position.

• Installation of perimeter jacks, their hydraulic connection with pumps. All perimeter jacks will be inter connected.

• Fix stretching screws, fix vertical steel holders in position.

• Place jack rods in position and should be truly vertical.

• Complete hydraulic connections.• Adjust the slope of the form panels as per the design

requirements.• Erect the water level system. All water tubes should

be interconnected. Mark the position of water level in the tube when the system is perfectly level.

• A leak tight jacking system shall be ensured.• Complete calibration of spider beams with respect to

reduction in radius at different elevations.• Erect all frames and pulleys on the deck for concrete

hoists, material hoists and passenger hoist.• Complete top deck, working deck, inner and outer

hanging scaffold lighting arrangement. Provide safety mesh on inner and outer hanging scaffolds.

• Complete curing arrangements. Finally check all connections.

• All arrangements of concrete mixing, transportation, placing of concrete, vibration, curing, materials transportation, movement of personnel and workers, power supply, water supply, lighting, lighting protection, signal and telecommunication systems, opening and blockouts, inserts, precision instruments for checking parameters, fire fighting, drinking water, concrete testing shall be made side y side so that all of these arrangements are completed by the time the slip form equipment has been fully erected.

Operations• 1st lift: The temporary stools or bracings on which the

yoke legs and shuttering framework has been supported are removed just before the concrete pouring is started.

1st lift to form panels is to be given only when the concrete poured in the forms have gained sufficient strength. The time to be allowed to lapse before 1st lift may lie between 4 to 8 hrs depending on the weather conditions.

• Reinforcement Steel.• Openings and inserts• Concrete

• Finishing smooth surfaces.• Control over parameters: Wall thickness Radius, length or breadth Verticality – tilt, twist Levels Slope of yoke legs Reference markings Extension of jack rods

• Tolerance limitsa) I.S.I. – so far no guidelines on slip forming or tolerance

limits in slip forming have been provided by I.S.I.b) A.C.I. 347-1978 specifies the permitted tolerances

which are as below: 1. Variation in verticality: 25mm per 15 m height

subject to max. of 75mm. 2. Variation in wall thickness: -10mm to +25mm 3. Variation in diameter: +25mm or +12mm per 3m dia.

whichever is more subject to max. of 75mm.c) NTPC has laid down the following construction

tolerance limits 1. Variation in verticality: 1 in 1000 (so that it shall be

15mm per 15 m height) 2. Variation in wall thickness: -5mm to +25mm 3. Variation in diameter: +75mm

d) Other organisations in India, generally allow following construction tolerances.

1. Variation in verticality: 25mm per 15 m height subject to max. of 70mm.

2. Variation in wall thickness: -5mm to +25mm 3. Variation in diameter: ±25mm or ±12mm per 3m dia.

whichever is more subject to max. of 70mm. 4. Variation in opening and blockouts Top level: 0 to +15mm Bottom level: -15mm to 0.0mm Sides: ±25mm but opening width not less than that

given in drawing 5. Twist in plan: Nil 6. Tilt: Nil

Dismantling of Slip formDismantling of slip form requires planning a dismantling sequence

minutely and implementation of plan under an expert eye.For dismantling cranes should be used to maximum possible

extent.In general the following sequence should be adopted:• 1. After completion of work and free lifting of form panels, the

shuttering is to be supported with timber props removing shuttering plates at support points so that walers and structural system of the shuttering could be supported properly. A temporary platform to support the working deck should be made. The weight of the whole of slip form assembly is transferred from jack rods to the finished structure, either through props or through bolts inserted through holes left in the walls below the walers.

• 2. Next, the hanging scaffolds should be removed and lowered to ground.

• 3. Next, the jack rods should be withdrawn.• 4. The jacks and hydraulic system should now be

dismantled.• 5. The electrical should next be removed.• 6. Next, the reinforcement holders and water level system

should be removed.• 7. The curing arrangements should next be removed.• 8. Now the external walers and form panels should be

removed.• 9. Working deck should next be removed.• 10. The internal form panels should now be removed.• 11. The jack rod holes should now be grouted.• 12. The structural system should now be removed.