SLAB:
Slabs are structural elements, made of concrete, which are
used to form floors, roofs, and ceilings in buildings. Slab carry uniform loads
which are distributed through beams, columns, walls on which it is supported.
Slabs may have a solid uniform thickness or with ribs running
from one or two directions.
Slabs differentiate as per the method of support used. They
are as given below:
Oneway slab: Spanning one way between the support walls or
beams.
Twoway slab: Spanning two way between the support walls or
beams.
Types of Slabs:
ONEWAY SLAB:
This type of slab has to support
on two opposite sides, therefore, the action i.e load is only in one direction
which also means the load transfer direction is perpendicular to the support beams.
The thumb rule to identify oneway slab is as follow:
If a slab is supported on all the 4 aspects but
the ratio of longer span (l) to shorten span (b) is more than 2, then the slab may be
considered as a oneway slab. Because due to the huge difference in lengths, the load
isn't transferred to the shorter beams. The main reinforcement is furnished in the handiest one path for oneway slabs.
One way slab is further differentiated into the following type:
TWOWAY SLAB:
Twoway slabs are the slabs that can be supported on four aspects and the ratio of longer span (l) to shorter span (b) is less than 2. In twomanner slabs, the load might be carried in each the guidelines. So, predominant reinforcement is supplied in both paths for 2way slabs.
Twoway slabs are of the following types:
LOAD TRANSFER ON ONEWAY & TWOWAY SLAB:
Reinforcement details of One way Slab:
Ribbed Slabs:
It is a system that consists of a chain of
parallel reinforced concrete T beams framing into reinforced concrete girders.
The slab is the flange of the beam and the extended part is the web. This
prolonged component is known as ribs. It is economical for medium spans with
small to medium loads.TWOWAY SLAB:
Twoway slabs are the slabs that can be supported on four aspects and the ratio of longer span (l) to shorter span (b) is less than 2. In twomanner slabs, the load might be carried in each the guidelines. So, predominant reinforcement is supplied in both paths for 2way slabs.
Twoway slabs are of the following types:
Waffle Slabs:
It's a twoway slab reinforced by using ribs
in two dimensions. Able to hold heavier loads and span longer than ribbed
slabs.
Flat slabs:
Slabs of uniform thickness which are bend and
reinforced in two directions and are supported directly by columns without
beams.
Also read: Thumb Rules for Civil EngineersFlat slabs with drop panel:
Drop panel is a region in the flat slab which is
provided to avoid a shear punch in the slab which generally occurs in and around
the area of the column. It is generally suitable
for heavily loaded span.
Difference
between Oneway slab and twoway slab:
S.No

Oneway Slab

Twoway Slab

1

If L/b the ratio is greater than or equal 2 or then it is
considered a oneway slab.

If L/b the ratio is less than 2 then it is considered a
twoway slab.

2

In a oneway slab, the crank is provided in two directions.

In a twoway slab, the crank is provided in four directions.

3

In a oneway slab, the main reinforcement is provided in a short span and distribution reinforcement is provided in a long span.

In a twoway slab, the main reinforcement is provided in both directions.

4

In oneway slab, the load is carried in one direction perpendicular
to the supporting beam.

In a twoway slab, the load is carried in both directions.

5

The oneway slab is supported by a beam on two opposite side
only.

The twoway slab is supported by the beam on all four sides.

6

The deflected shape of the oneway slab is cylindrical.

Whereas the deflected shape of the twoway slab is a dish or saucerlike shape.

7

While designing oneway slab we provide less steel hence
the depth of the slab increases, as a result, the thickness of the oneway
slab is more as compared to the twoway slab.

While designing twoway slab we provide more steel hence the
depth of slab decreases, as a result, the thickness of twoway slab is less
as compared to the oneway slab.

8

The oneway slab is economical up to a span of 3.6 meters.

Whereas the twoway slab is economical for the panel sizes up to 6m × 6m.

9

In oneway slab, bending is only in one direction i.e. in a
shorter span.

In a twoway slab, bending is in both directions.

10

In a oneway slab quantity of steel is less.

In twoway slab quantity of steel is more as compared to the
oneway slab.

11

Terrace and Varandha are practical examples of oneway slab

Whereas twoway slabs are used in constructive floors of the Multistory
building.

In practices, the choice
of the oneway slab and twoway slab for a particular structure will largely
depend upon the
 Economy
 Buildability
 Loading condition
 Length of span
Reinforcement details of One way Slab:
Here L/B = 10/4 = 2.5 ≥ 2
From the above drawing
it is clear that L/B is greater then 2, hence it is a oneway slab. So the main
bar or cranked bars are provided in shorter span and distribution bars are
provided in the longer span.
Reinforcement details of Two way Slab:
Here L/B = 6/6 = 1 < 2
From the above drawing, it is clear that the L/B ratio is less than
2, hence it is a twoway slab, that’s why main bars or cranked bars are
provided at a longer span as well as shorter span also.
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