# One way slab and two way slab differences and reinforcement

One-way and two-way slabs differ in their structural behavior and the distribution of loads.

1. One-way slab: It is supported on two opposite sides only and primarily bends in one direction. The reinforcement is placed in the direction perpendicular to the shorter span. Commonly used when the ratio of longer span to shorter span is greater than 2.

2. Two-way slab: It is supported on all four sides and bends in both directions. Reinforcement is provided in both directions to resist bending moments. This type is suitable when the ratio of longer span to shorter span is less than or equal to 2.

One way slab and two way slab differences and reinforcement details, hi guys in this topic we know about one way slab vs two way slab and what is difference between one way slab and two way slab and also know about reinforcement details.

Slab of floors and roof of building mostly integrated with supporting beams carry distribution load primarily by bending. Slab are either of single span or continuous having different support condition lile fixed, hinged or free along the edges.

Normally slabs are horizontal, inclined slabs are also used in ramps, staircase and inclined roofs. While square or rectangular plan forms are normally used,triangular circular and other plan forms are also needed for different functional requirement.

In this topic we take up horizontal and rectangular square slab of building supported by beams in one or both direction and subjected to informally distributed vertical loadings.

One way slab is a slab which is supported by beams at least two opposite sides to carry the load along One Direction, in one way slab the ratio of longer span to shorter span is equal or greater than 2.

It Does not means that one way slab is only supported by two beams in opposite direction, four beam may be possible, but why it is one way slab? because only condition is that load is carry in only longer is span direction in opposite side. So must be cared about it four supported beam may be possible in one way slab but load is carrying only in longer span direction in opposite sides.

Two way slab is a slab which is supported by four beams and load is uniformly distributed in all for sides of wall beam. in two way slab the ratio of longer span to shorter span is less than 2.

Majors discipline in two way slab is presence of all four beams in both opposite direction and second one is load is uniformly distributed in all four sides of wall beam vertically.

Main difference between one way and two way slab is that in one way slab load is carried in longer span of both opposite sides but in two way slab load is uniformly distributed in all four sides of wall beam vertically.

## What is one way slab?

One way slab is a slab which is supported by at least two beams in opposite sides to carry the load along One Direction, in one way slab the ratio of longer span to shorter span is equal or greater than 2.

In cross-section suppose longer span is ly and shorter span is lx, then ratio of longer span and Shorter span ( longer span/shorter span = ly/lx ≥ 2.

in cross section suppose longer span is 5000mm and shorter span is 2000mm then ly/lx = 5000/2000 = 2.5, hance 2.5 > 2, hance it will be one way slab.

Major point in one way slab:-

● 1) one way slab supported by at least two beams, also four beams may be possible but load is acting only in the longer span direction in opposite sides,not in shorter span direction.

● 2) in one way slab load is acting vertically and carried in one direction of longer span of opposite sides. General load is acting in one direction.

● 3) in one way slab the ratio of longer span to shorter span is equal or greater than 2,ly/lx ≥ 2.

● 4) it will provide main reinforcement or crank bar in shorter Span direction only and distribution bar is provided in longer span transversely to main bar.

● 5) generally thickness of one way slab is Greater as compared to two way slab to maintain strength of concrete slab which minimising strong tension zone in developed in one direction.

● 6) generally design of one way slab is less economical (costlier) as compare to two way slab.

## What is two way slab?

Two way slab is a slab which is supported by at least four beams in all sides to carry the load uniformly distributed in all four Direction, in two way slab the ratio of longer span to shorter span is less than 2.

In cross-section suppose longer span is ly and shorter span is lx, then ratio of longer span and Shorter span ( longer span/shorter span = ly/lx < 2

in cross section suppose longer span is 3000mm and shorter span is 2000mm then ly/lx = 3000/2000 = 1.5, hance 1.5 < 2, hance it will be two way slab.

Major point in two way slab:-

● 1) two way slab supported by at least four beams, roof slab containing two beam support, it will not be two way slab. So major requirement in two way slab is presence of at least four Beams.

● 2) in two way slab load is acting vertically and carried uniformly distributed all four sides of wall beam, it will distributed in both longer span and shorter span all sides, so tension in all members are equal.

● 3) in two way slab the ratio of longer span to shorter span is less than 2, ly/lx < 2

● 4) it will provide main reinforcement or crank bar in both direction longer span as well as shorter Span and distribution bar is provided in longer span transversely to main bar.

● 5) generally thickness of two way slab is less as compared to one way slab because it has enough strength to minimise tension developed in all four sides.

● 6) generally design of two way slab is more economical (cheaper) as compare to one way slab.

## Difference between one way slab and two way slab.

As You understand what is one way slab and two way slab, now try to find out major difference between one way slab and two way slab and one way slab vs two way slab.

### One way slab vs two way slab

● 1) one way slab supported by at least two beams, also four beams may be possible but load is acting only in the longer span direction in opposite sides,not in shorter span direction.

But two way slab supported by at least four beams, roof slab containing two beam support, it will not be two way slab. So major requirement in two way slab is presence of at least four Beams.

● 2) in one way slab load is acting vertically and carried in one direction of longer span of opposite sides. General load is acting in one direction.

But in two way slab load is acting vertically and carried uniformly distributed all four sides of wall beam, it will distributed in both longer span and shorter span all sides, so tension in all members are equal.

● 3) ) in one way slab the ratio of longer span to shorter span is equal or greater than 2,ly/lx ≥ 2.

But in two way slab the ratio of longer span to shorter span is less than 2, ly/lx < 2

● 4) one way slab will provide main reinforcement or crank bar in shorter Span direction only and distribution bar is provided in longer span transversely to main bar

But in two way slab will provide main reinforcement or crank bar in both direction longer span as well as shorter Span and distribution bar is provided in longer span transversely to main bar.

● 5) generally thickness of one way slab is Greater as compared to two way slab to maintain strength of concrete slab which minimising strong tension zone in developed in one direction.

● 6) generally design of one way slab is less economical (costlier) as compare to two way slab.

You should also visits:-

1)what is concrete and its types and properties

2) concrete quantity calculation for staircase and its formula