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SLIP FORMWORKGUIDED BY Prof. VRK MURTHY SUBMITTED BY Vikas B. More (73036) Aniruddha S. Namojwar(73038)

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DefinitionThe 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.

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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.

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Outside yoke leg main yoke

Distance bar

Outside yoke leg with U normal

Beam for bracing of main yoke

Outside hanging scaffold

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ShutteringForm 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 jointsor overlaps may cause a drag component in horizontal direction which will causetorsional effects on slip form assembly.

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WalersStiffen 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. Ifthe yoke panel is more than 3.0m in span, the walers are to be braced suitably.

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YokesConsist of yoke legs and yoke beams All 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.

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Working decksThe working decks are required for complete operation of slip form equipment andbringing up all type of materials, equipment, concrete, staff and workers. Deckis 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.

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The number of main trusses and spider beam may vary depending upon the number ofyokes to be used which further depends upon the diameter of the structure. Thesliding 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.

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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.

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Lifting equipmentsjacking system. lifts the slip form equipment assembly as a whole including allthe structural frame work, yokes, walers, hanging scaffolds, all the decks, allthe live loads and service loads. It comprises of three components: Jacks Jack rods or pipes Pumping station in case of hydraulically operated jacks.

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Other Miscellaneous EquipmentsBracings Screws: Radius and wall thickness screws Stretching screws Safety netsExtraction jacks Grouting pump The number of items required for a complete slipform assembly may vary for different type of structures with respect to their structural and dimensional requirements.

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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, theaccuracy of the parameters and the quality of the slip formed structure dependsupon the exactness in erection of slip form equipment. Sequence of erection ingeneral: 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.

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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.

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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 curingarrangements. 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.

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Operations1st lift: The temporary stools or bracings on which the yoke legs and shutteringframework 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 before1st lift may lie between 4 to 8 hrs depending on the weather conditions. Reinforcement Steel. Openings and inserts Concrete

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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

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Tolerance limits a) 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 per15 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 tolerancelimits 1. Variation in verticality: 1 in 1000 (so that it shall be 15mm per 15 mheight) 2. Variation in wall thickness: -5mm to +25mm 3. Variation in diameter:+75mm

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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 openingand blockouts Top level: 0 to +15mm Bottom level: -15mm to 0.0mm Sides: 25mm butopening width not less than that given in drawing 5. Twist in plan: Nil 6. Tilt: Nil

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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 usedto maximum possible extent. In general the following sequence should be adopted: 1. After completion of work and free lifting of form panels, the shuttering isto be supported with timber props removing shuttering plates at support pointsso that walers and structural system of the shuttering could be supported properly. A temporary platform to support the working deck should be made. The weightof the whole of slip form assembly is transferred from jack rods to the finishedstructure, either through props or through bolts inserted through holes left inthe walls below the walers. 2. Next, the hanging scaffolds should be removed and lowered to ground.

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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.

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