LIFT SLAB

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					                          LIFT SLAB
                        CONSTRUCTION
•   IT IS THE SYSTEM OF CONSTRUCTION IN WHICH THE FLOOR SLAB AND THE
    FLAT ROOF ARE CAST ONE OVER THE OTHER AT GROUND LEVEL AT AROUND
    COLUMNS OR IN SITU CAST SERVICE , STAIRS AND LIFT CORES.
•   JACKS OPERATING FROM THE COLUMNS OR CORES PULL THE ROOF AND
    FLOOR SLABS UP INTO POSITION.
•   THE CONSECUTIVE SLABS ARE SEPARATED THROUGH A MEDIUM LIKE- WAX
    DISSOLVED IN VOLATILE SPIRIT OR POLYTHENE SHEETS OR BULIDING
    PAPER.
•   THE SLABS ARE CAST MONOLITHICALY AND CAN BE DESIGNED TO SPAN
    CONTINUOUSLY BETWEEN AND ACROSS POINTS OF SUPPORT AND SO
    EMPLOY LEAST THICKNESS OF SLAB.
•   BALCONIES AND OTHER EXTENSIONS CAN BE EXTENDED BEYOND THE EDGE
    COLUMNS AS PART OF THE SLAB.
STAGES IN CONSTRUCTION
                  STAGES IN CONSTRUCTION
•   THE STEEL AND CONCRETE COLUMNS ARE FIRST FIXED IN POSITION AND
    RIGIDLY CONNECTED TO THE FOUNDATION AND THE GROUND FLOOR SLAB IS
    THEN CAST.
•   WHEN IT HAS MATURED IT IS SPRAYED WITH TWO OR THREE COATS OF A
    SEPARATING MEDIUM CONSISTING OF WAX DISSOLVED IN A VOLATILE
    SPIRIT.
•   POLYTHENE SHEET OR BUILDING PAPER MAY ALSO BE USED AS AN
    ALTERNATIVE.
•   THE FIRST FLOOR SLAB IS CAST INSIDE EDGE FORMWORK ON TOP OF THE
    GROUND FLOOR SLAB AND WHEN IT IS MATURE IT IS IN TURN COATED OR
    COVERED WITH THE SEPARATING MEDIUM AND NEXT FLOOR SLAB IN CAST
    ON TOP OF IT.
•   THE CASTING OF SUCCESIVE SLAB CONTINUES UNTIL ALL THE FLOORS AND
    ROOF HAVE BEEN CAST ONE ON THE OTHER ON THE GROUND.
•   LIFTING COLLARS ARE CAST INTO EACH SLAB AROUND EACH COLUMN.

•   THE SLAB ARE LIFTED BY JACKS , OPERATING ON THE TOP OF EACH
    COLUMN,WHICH LIFT A PAIR OF STEEL RODS ATTACHED TO EACH LIFTING
    COLLAR IN THE SLAB BEING RAISED.
•   A CENTRAL CONTROL SYNCRONISES THE PROCESS FOR A UNIFORM LIFT FROM
    ALL DIRECTIONS.
LIFTING STAGES IN A 3 STOREY BUILDING




             LIFTING COLLAR
•   THE SEQUENCE OF LIFTING SLABS IN DEPENDS UPON:
          WEIGHT OF THE SLABS
          HEIGHT OF THE BUILDING
          LIFTING CAPACITY OF JACKS
          CROSS SECTIONAL AREA OF COLUMNS DURING INITIAL LIFTING

•   THE BASE OF THE COLUMNS ARE RIGIDLY FIXED TO THE FOUNDATIONS SO
    THAT DURING LIFTING THEY ACT AS VERTICAL CANTILEVERS.
•   THE LOADS THAT THE COLUMN CAN SUPPORT AT THE BEGININNG OF THE LIFT
    LIMITS THE LENGTH OF THE LOWER COLUMN HEIGHT AND NO. OF SLABS
    THAT CAN BE RAISED ONE AT A TIME.
•   AS THE SLABS ARE RAISED THEY SERVE AS HORIZONTAL PROPS TO VERTICAL
    CANTILEVERS AND SO INCREASINGLY STIFFENING THEM.

LIFTING COLLARS

   THEY ARE CAST INTO EACH SLAB AROUND EACH COLUMN PROVIDING A MEANS
    TO LIFT THE SLAB AND ALSO PROVIDING SHEAR REINFORCEMENT
   THEY ARE FIXED TO COLUMNS BY WELDING SHEAR BLOCKS TO PLATES WELDED
    B/W COLUMN FLANGES AND TO THE COLLAR AFTER THE SLAB HAS BEEN RAISED
    IN POSITION.
•   THE CONNECTIONS TO CONCRETE COLUMNS ARE MADE BY WELDING SHEAR
    BLOCKS TO END OF STEEL CHANNELS CAST INTO THE COLUMN AND BY
    WELDING THE COLLAR TO THE WEDGES.
•   CONCRETE IS CAST AROUND STEEL WEDGES FOR FIRE PROTECTION.

•   THE CONNECTIONS OF EXTENSION COLUMNS ARE MADE BY WELDING,
    BOLTING OR RIVETING SPLICE PLATES TO THE FLANGES OF COLUMNS AT THEIR
    JUNCTIONS.




ADVANTAGES OF THE SYSTEM
•   CAN BE AN ADVANTAGEOUS AYSTEM IN BUILDINGS WITH SIMILAR FLOOR
    PLANS THROUGHTOUT THE HEIGHT OF THE BUILDING AND WHERE FLUSH SLAB
    MAY BE DESIRED.
•   ELIMINATES NEED FOR REDUNDANT FORMWORK AS ONLY SHUTTERING
    REQUIRED ON THE EDGES- HENCE SIMPLICITY IN CASTING.
•   MAY ALSO BE EMPLOYED TO GIVE WAFFLE GRID HOWEVER COMPRIMISING ON
    THE EASE OF CASTING.
                          DROP SLAB

•   HIS FLOOR CONSTRUCTION CONSISITS OFA FLOOR SLAB WHICH IS
    THICKENED B/W COLUMNS IN THE FORM OF ASHALLOW BUT WIDE BEAM
•   A DROP SLAB FLOOR IS OF ABOUT THE SAME DEAD WEIGHT AND COST
    AS A COMPARABLE SLAB AND BEAM FLOOR AND WILL HAVE UPTO HALF
    THE DEPTH OF FLOOR CONSTRUCTION FROM TOP OF SLAB TO SOFIT OF
    BEAMS.
•   FOR EXAMPLE ON A TWELVE SQUARE COLUMN GRID THE OVER ALL DEPTH
    OF THE SLAB AND THE BEAM FLOOR WOULD BE ABOUT 1.2 WHERE THE
    DEPTH OF A DROP SLAB FLOOR WOULD BE ABOUT 600.
•   CONSEQUENTLY THIS DIFFERENCE WOULD CAUSE A SIGNIFIGANT
    REDUCTION ION OVER ALL HEIGHT OF CONSTRUCTION OF A MULTI
    STORY BUILDING WITH APPRECIABLE SAVINGS AND COST.

				
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posted:11/15/2012
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