One-Way Slab

As per is 456-2000, in case of one-way slab the ratio of longer span to shorter span is equal or greater than 2.

That is – L/W ≥ 2


Example:

Consider is a slab of 8m X 3m
(8m is the longer span & 3m is the shorter span).

So, 7m / 3m = 2.666m
؞ 2.666m ˃ 2

This is called a one-way slab.


Bending Moment:

In the case of a one-way slab, the slab bends in only one direction. That is in the direction along its shorter span.



Deflected Shape:

The deflected shape of a one-way slab is cylindrical.


Support:

In a one-way slab, the slab is supported by the beams on two opposite sides.
                          
Example: Chajja, Veranda



Load Carrying Direction:

In one way slab the loads are carried along one direction.


Reinforcement:

In a one-way slab, slab bends in one direction. And it’s to counter on the bending in main steel, cranked bar or extra bar are provided in the shorter direction.
                       





Slab Thickness:

When designing a one-way slab, we provided less steel. Hence the depth of slab increases. As a result, the thickness of the one-way slab is more as compact as a two-way slab.


Use:

The one-way slab can be economical up to a span of 3.6m.



Two-Way Slab

As per IS 456-2000, in the case of the two-way slab the ratio of longer span to shorter span is less than 2.

That is - L/W < 2

Example:

Consider is a slab of 5m X 5m
(5m is the longer span & 5m is the shorter span).

So, 5m / 5m = 1.0m
؞ 1.0m < 2

This is called a two-way slab.


Bending Moment:

In the case of a two-way slab, the slab bends in both directions.



Deflected Shape:

The deflected shape of the two-way slab is a dish.


Support:

In a two-way slab, the slab is supported by the beams on all four sides.

Example: The two-way slab is used in the floor of a multi-story building.



Load Carrying Direction:

In two way slab the loads are carried along with both directions.


Reinforcement:

In a two-way slab, slab bends in both directions. And the main steel cranked bar or extra bar is provided on both directions to counter this bending.




                          
Slab Thickness:

When designing a two-way slab, we provided more steel. Hence the depth of slab decreases. As a result, the thickness of the two-way slab is less as compact to a two-way slab.


Use:

The two-way slab can be economical for the panel sizes up to 6m X 6m.