2. What is Slab?
“A flat piece of concrete, typically used as a
walking surface, but may also serve as a load
bearing device as in slab homes.”
Used for covering spaces in the form of roof or
floor .
Slab may be supported on walls or beams or
Columns.
3. FUNCTION OF SLAB
Provide a flat surface.
To support load.
Sound, heat and fire insulator.
Act as a divider (privacy) for the occupants.
Upper slab became the ceiling for the
storey below.
Space between slab and false ceiling can be
used to place services of building.
7. ONE WAY SLAB
• One-way slabs are those slabs with an aspect ratio in
plan of 2:1 or greater, in which bending is primarily
about the long axis. So, the slab is one way where
L/B ≥ 2.
• The Slab supported on two opposite side only in
which the structural action of the slab is essentially
one way.
• Direction of load carried by the slab is perpendicular
to the supporting beams.
• Slab depths are usually 4-10 inches (100-150mm).
• Uneconomical on spans of more than 20’(6000mm) .
9. Provides useful flat surface
One way slab may be used when
there is architectural limitations
It is the simplest form of slab
design
Main reinforcement placing is
one way, so there is a little
congestion than two way slab
APPLICATION OF ONE WAY SLAB
10. Two-way slab
There may be beams on all
four side , so two way slab
action is obtained.
Two-way slabs carry load in
two directions.
“Generally, two way floor
systems are more
economical than one-way
systems in buildings where
columns can be spaced in
bays that are square or
nearly square in proportion”
12. • In slab the corners may be held down by restraints or may be allowed to
lift up
• Additional torsion reinforcement is required at corners when it is
restrained against uplifting as shown .
13. Solid Flat Slab System.
• Floor systems can made without beams. Instead,
“the slab is reinforced in such a way that the varying
stresses in the different zones of the slab are
accommodated within a uniform thickness of
concrete”
• Slab depth =250 MM
• Suitable span 6 to 9m
Advantages
– Low cost formwork
– Exposed flat ceilings
– Fast
14. Disadvantages
•Due to continuous pressure at point (less surface area), it
create punching shear cracks at joints.
•Require more form work for panels and Capitals.
17. • “In more lightly loaded buildings, such as hotels,,
dormitories, and apartment buildings, the slab need
not be thickened at all over the columns.”
• Slab depth =.
• Suitable span 4.5m to 6.0m
Advantages
– Low cost formwork
– Exposed flat ceilings
– Fast
Disadvantages
– Low shear capacity
– Low Stiffness (notable deflection)
Flat Plate System
28. • Thickness of the slab is decided based on
span to depth ratio for mild steel bars.
• The maximum diameter of bar used in slab
should not exceed 1/8 of the total thickness
of slab
• Maximum spacing of main bar is restricted to
3 times effective depth or 300 mm which
ever is less
• For distribution bars the maximum spacing is
specified as 5 times the effective depth or
450 mm which ever is less
DESIGN CRITERIA FOR REINFORCEMENT
29. TYPES OF SLAB PROBLEM
Cracking Of The Slab
Damp Or Wet
Floor Slab
30. CRACKING OF THE SLAB : CAUSES
Inadequate structural strength of concrete
Improper placement of reinforcing & mesh
Poor construction
techniques and
practices
Differential / Uneven
settlement
31. Damp or Wet Floor Slab : Causes
Moisture migration through the slab
Poor site drainage
