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# Differences between One Way Slab and Two Way Slab

## What are the Differences between One Way Slab and Two Way Slab?

Most civil engineering students’ gets confused when asked about the questions related to the differences between one way slab & two way slab. If you want to know about their differences, this article explains it in detail with definitions and comparison chart.

Before going into the list of differences between one way & two-way slab, we are going to discuss what Slab is & what the types of slab are & what differentiates them from each other.

### SLAB:

Slab is the horizontal member of structure the top and bottom surfaces of slab is parallel to each other. The depth of slab is very small compared to its span. slab is constructed on the top of walls, beams or columns of the structure. In multi-story building the top slab is called roof slab & in the lower slab are called floor slab. Slab may be constructed from different materials such as steel, concrete, bricks etc. it creates flat horizontal surfaces like floors, roof decks and ceilings. Usually the depth of slab is slightly thick and supported by beams, columns, walls, or the ground.

Slabs are classified into two types:

• One Way Slab
• Two Way Slab

#### One Way Slab

According to IS 456:2000 the slab in which the ratio between longer span (L) and shorter span (B) is equal or greater than 2 is called one way slab. In case of one way slab the load is carried in one direction & on that direction main bars are designed & on the other direction thin bars are used compered to main bars which are called distribution bars.

One way slab = Longer span / shorter span > 2

Verandah is the best example of one way slab.

Figure of One way slab

#### Two Way Slab

The slab in which the ratio between the longer span (L) & the shorter span (B) is less than 2 is called two way slabs. In case of two way slab loads are distributed in both direction and it is supported from all sides which is why the load can be distributed on both direction in square shape area the main bars can be used on the either side but the main bars will always beneath the distribution bars but if the shape of area is in rectangular shape then the main bars should be used in the shorter direction & distribution bars should be used in the longer direction.

Two way slab = Longer span / shorter span < 2

Figure of Two way Slab

### Differences between One Way Slab & Two Way Slab:

The difference between One Way Slab & Two Way Slab are shown in the table which is given below:

 S. No One Way Slab Two Way Slab 1 The length of the longer span is two times equal or greater than the length of the shorter span The length of the longer span is equal or less than two times length of shorter span. 2 In IS code 456:2000, The ratio of longer span (L) to shorter span(b) which is (L/B) greater than 2 is known as One way slab In two way slab, the ratio of longer span to shorter span is less than 2. 3 Based on the deflection and considering the span the thickness of slab may vary from 4 inch to 6 inch(100mm to 150mm) Based on the deflection and considering the span the thickness of the slab may vary from 4 inch to 8 inch (100mm to 200mm) 4 One way slab is reinforced by beams on the 2 shortest sides to transmit the load along one direction. Two way slab is reinforced by beams on all the 4 sides and the loads are transmitted by the supports along both directions, 5 One way slab curves, deflect or bend in a direction vertical to the supporting ends Two way slab curves, deflect or bend in both directions. 6 Bent shape of one way slab is cylindrical. Bent shape of two way slab is dish-shaped. 7 One way slab has strength in shortest direction. These types of slab are used for verandah and terrace. Two way slab has strength in both direction. These types of slabs are mostly used in the floor of multistory buildings. 8 Main reinforcement is provided on shorter direction due to the bending. Main reinforcement is provided in both directions due to bending happens on both sides. 9 One way slab is economical as compared to two way slab It’s more expensive compared to one way slab because steel bars are used more in it. 10 In one way slab the load is carried on one direction In two way slab the load is carried  on both direction 11 Beams  supported the One way slabs on two sides Beams  supported the two way slabs on four sides 12 Mostly the shape of one way slab is rectangular Mostly the shape of two way slab is square. 13 The design of one way slab is totally different from two way slab. Design of two way slab there equations, steps of methods everything is different from one way slab. 14 In one way slab the extra bar or crank bar are provided on one direction or on two sides In two way slab the extra bar or crank bar are provided on both direction or on four sides 15 The Deflection of one way slab looks like cylindrical. The deflection of two way slab looks like bowl

#### Conclusion:

The main objective of this article “Differences between One Way Slab & Two Way Slab” is that the ratio between longer span to shorter span will be greater than two (2) in one way slab and carried the load on only one direction while in two way slab the ratio between longer span to shorter span will be less than two (2) and carried the load on both direction.