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FLAT SLAB FLOORS

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					       FLAT SLAB FLOORS
• It is made up of R.C.C slab.
• In this the thickness of slab is
   uniform.
• Directly supported on
  columns.
• They are generally thicker
  than beam.
• Economical in heavy loads.
• Column spacing ranges between 5-8 meters.
 ADVANTAGES OF FLAT SLAB
        FLOORS
• Formwork required for this is very simple
  and cheap.
• It gives a good appearance.
• It gives better lighting facilities.
• It is specially suited for the heavy live
  loads.
• It also affords the convenience of hanging
  pipes which is added advantage in
  factories.
      ESSENTIAL FEATURE OF
    CONSTRUCTION OF FLAT SLAB
             FLOOR

•   Economy in construction cost.
•   No false ceiling is required.
•   Construction technique is simple.
•   More clear headroom is available.
   SPECIALLY USED UNDER
    CERTAIN CONDITIONS
• Where large clear spaces are used.
• The end spans should not be more than the
  interior spans.
• Where head room is limited.
• The ratio of length to breadth of panels
  should not be more than 4:3.
• Where heavy loads are to be carried.
• Generally used for buildings such as
  factories, mills, theatres, public buildings
  etc.
 REINFORCEMENT IN FLAT
      SLAB FLOORS
1. Two-way system: In this reinforcement
   is carried from column to column and at
   right angles to one another.
2. Four-way system: In this reinforcement
   is placed in four directions. Consists of
   two bands of main steel from column to
   column and other two bands placed
   diagonally across the panel from column
   to column.
TWO-WAY SLABS
   FLAT SLAB
REINFORCEMENT
    DROP BEAM AND SLAB
•   THIS FLOOR CONSTRUCTION CONSISTS OF A FLOOR
    SLAB WHICH IS THICKENED BETWEEN COLUMNS IN
    THE FORM OF A SHALLOW BUT WIDE BEAM.
•   A DROP SLAB FLOOR IS OF ABOUT THE SAME DEAD
    WEIGHT AND COST AS A COMPARABLE SLAB AND
    BEAM FLOOR.
•   IT WILL HAVE UP TO HALF THE DEPTH OF FLOOR
    CONSTRUCTION FROM TOP OF SLAB TO SOFFIT OF
    BEAMS.
•   THIS DIFFERENCE WOULD CAUSE A SIGNIFICANT
    REDUCTION IN OVERALL HEIGHT OF
    CONSTRUCTION OF A MULTI-STOREY BUILDING
    WITH APPRECIABLE SAVING IN COST.
DROP BEAM AND SLAB

         •   DROP SLAB FOOR HAS UP
             TO HALF THE DEPTH OF
             FLOOR CONSTRUCTION
             FROM TOP OF SLAB TO
             SOFFIT OF BEAMS.

         •   FOR e.g.- ON A 12.0 SQUARE
             COLUMN GRID THE
             OVERALL DEPTH OF A SLAB
             AND BEAM FLOOR BE
             ABOUT 1.2 WHERE THE
             DEPTH OF A DROP SLAB
             FLOOR WOULD BE ABOUT
             600.
DROP BEAM AND SLAB

                REINFORCED
                CONCRETE
                COLUMNS




               REINFORCED
               CONCRETE SLAB
               DROPPED BETWEEN
               COLUMNS TO FORM
               SHALLOW WIDE
               BEAMS
     DROP BEAM AND SLAB
    FROM ACI 318 BUILDING CODE
•   FOR MONOLITHIC OR FULLY COMPOSITE CONSTRUCTION, A
    BEAM INCLUDES THAT PORTION OF SLAB ON EACH SIDE OF
    THE BEAM EXTENDING A DISTANCE EQUAL TO THE
    PROJECTION OF THE BEAM ABOVE OR BELOW THE SLAB’
    WHICHEVER IS GREATER, BUT NOT GREATER THAN FOUR
    TIMES THE SLAB THICKNESS.
•   WHEN USED TO REDUCE THE AMOUNT OF NEGATIVE
    MOMENT REINFORCEMENT OVER A COLUMN OR MINIMUM
    REQUIRE SLAB THICKNESS, A DROP PANEL SHALL PROJECT
    BELOW THE SLAB AT LEAST ONE-QUARTER OF THE SLAB
    THICKNESS BEYOND THE DROP AND EXTENT IN EACH
    DIRECTION FROM THE CENTER LINE OF SUPPORT A
    DISTANCE NOT LESS THAN ONE-SIXTH THE SPAN LENGTH
    MEASURED FROM CENTER-TO-CENTER OF SUPPORTS IN
    THAT DIRECTION.
WAFFLE SLABS
• A Waffle slab is a two-way
concrete slab reinforced by ribs in
two directions.
• In this type of slab intermediate
beams are cast on a regular
square grid that gives the
underside of the floor appearance
of waffle , hence it is named as
waffle slab.
• Waffle slab construction is used
for ceilings and floor
constructions.
Benefits of Waffle Slab System
•Dead weight of the slab is reduced as
compared to flush slab of similar span
, as the intermediate beams of waffle
supports the thin slab above it.
   In these systems Bulk of cement
concrete below the neutral axis is
removed , as concrete below the
neutral axis is considered as having no
tensile value, except to resist shear
stresses . Hence certain portion of the
concrete is removed , leaving a
sufficient number of ribs or concrete
joists at short intervals carrying
reinforcement to take care of shear
stresses.
•Waffle slabs are able to carry heavier loads and span longer distan
than flat slabs as these systems are light in weight.
•Suitable for spans of 7m – 16m ; longer spans may be possible wit
posttensioning.
•It is also economical as the amount of concrete and steel is reduc
compared to flush slabs. Saving 15% concrete and 10% steel as com
to traditional T beams.
•These systems are light in weight and hence considerable saving i
ensured in the framework as light framework is required.
•Coffered underside is usually left exposed..
 Demerits of Waffle Slab System
•Construction requires strict supervision and skilled labour.
•The casting forms or moulds required for pre-cast units are very co
hence only economical when large scale production of similar units
desired.
•Headroom is reduced , hence increased storey height.
•Due to waffle ceiling , it creates problem in lighting facilities and h
pipes or ducts.
Details of Waffle Slab System


                      •Square metal or fiberglass dome form
                      available in 485mm and 760mm width
                      form 205mm to 510 mm depth in 51
                      increment. Larger size are also availab
                      •485mm dome with 125mm ribs create
                      610mm module and 760mm domes wi
                      rib creates 915mm module.
                      •Slab depth is usually taken between 7
                      115mm but by the thump rule it is take
                      span/24.
                      •Tapered sides allow for easier remova
                      •It is suitable for span 7m – 16m.
•For greater shear strength and
moment –resisting capacity , solid
heads at the column supports are
formed by omitting dome forms ; size
depends on the span on the load
conditions.
•For maximum efficiency , bays
should be square or nearly square as
possible.
•Waffle slab can be cantilevered in
two direction up to 1/3 of the main
span.
•The waffle grid form is cast around
plastic or metal formers laid on the
timber centering , these formers are
screwed to the centering , so that
smooth finish of the soffit is left
exposed.
Waffle Slab System Floor Construction
This type of floor is useful where
a widely spaced column grid is
necessary and the floor supports
heavy load because of the use of
intermediate cross beams.

•Ensure building site is level and all
plumbing pipes are fixed in place as
per plan.

•Spread a layer of sand or metal dust
approximately 50 mm thick over
building area . Place plastic sheeting
and tape laps.
• Set up formwork, set
  out Waffle Raft Pods in
  a grid pattern using
  multispacers provided
  which form all beams.




• Cut the Waffle Raft
  Pods to fit around
  plumbing pipes etc.
  using sharp handsaw
  or power saw. Place
  reinforcing bars in
  multispacers
  positioned between
• Place steel mesh on top of
  Waffle Pods and in the
  ribs



• Pour concrete, part fill the
  ribs to hold the Waffle Raft
  Pod in position before
  pouring 85 mm thick slab
  with 25 mm minimum
  cover over reinforcing
  mesh
             Benefits of the Waffle Slab System floor
              over conventional slab floor system

1.     Reduced building costs on sites containing :
            reactive soils ,sand ,rock ,water tables
 2.   Less use of concrete .
 3.   Greater strength and stiffness over conventional slab systems
 4.    Savings in construction time over conventional slab systems.
5.    Insulation benefits .
6.    Effective termite protection.

				
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posted:11/15/2012
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