## Difference Between One Way Slab And Two Way Slab

Hello Friends,

In this article, we will discuss the differences between the one-way slab and two-way slab.

Let’s start

## What is Slab

Slabs are mostly used as Roof covering and floors in various shapes such as square, rectangular, circular, and triangular in buildings, tanks & bridges.

In a structural system, slab forms the floor system which resists generally gravity loads (dead loads and live loads) acting on it and transmits these to the vertical framing system like columns. Slabs are frequently used as floors and roofs in building, decks in bridges, top & bottom of tanks, slabs on grade (grade slab)staircases, etc.

Slabs impart a very large volume of concrete in the building and hence the mass of the slabs attracts large lateral forces during the earthquake.

The floor/roof slabs and footing impart the maximum volume of concrete in the structure, and hence, the slightest reduction in design depth (as per codal provision) leads to a considerable economy.

Slabs can be solid, ribbed, and waffle types. Depending on their load-carrying behavior they are classified as one-way slab and two-way slab.

In practice, the choice of one-way slabs and two-way slab for a particular structure will largely depend upon the economy, build-ability, loading condition, and the length of the span. Here are the differences between a one-way slab and a two-way slab.

**Difference Between One Way Slab And Two Way Slab**

**What is a One-way Slab?**

As per IS Code 456: 2000 in the case of one way slab the ratio of longer span to shorter span is equal or greater than 2. that is

Longer span(I)/shorter span(b) > 2.( greater than 2).

**Lets Example of one-way slab**

Consider the slab of 6 m x 2 m in which 6 mtr is the longer span(I) and 2 mtr is the shorter span(b).

So, 6/2 = 3 > 2

Which is greater than 2, Hence it is called the one-way slab.

Examples:- the chajjas and the veranda are the practical example of a one-way slab.

**Related Video**

**What is Two-way Slab**

Whereas in the case of the two-way slab the ratio of longer span to shorter span is less than 2.that is

Longer span(I)/shorter span(b) < 2. ( less than 2).

**Let’s take the example of two-way slab**

Consider the slab of 3 m x 2 m in which 3 mtr is the longer span and 2 mtr is the shorter span.

L/W < 2

So, 3/2 = 1.5 which is less than 2 hence we can call the slab as a two-way slab.

Two-way slabs are used to constructed floors of multi-storied buildings.

**Difference Between One Way Slab And Two Way Slab**

**1). Bending Moment**

In the case of **one way slab** the slab bend in only one direction that is in the direction along the shorter span.

Whereas, In the case of the **two-way slab** the slabs bend in both directions.

**2). Deflection Shape**

The deflected shape of the **one-way slab** is cylindrical whereas the deflected shape of the **two-way slab** is dish or saucer shape.

**3). Supports**

In **one way slab**, the slabs are supported by the parallel beams or walls on two opposite sides whereas,

in **two-way slabs**, the slabs are supported by parallel beams on all the four sides.

**4). Load Carrying Direction**

In **one way slabs**, the loads are carried along one direction.

Whereas,

In **two-way slabs**, loads are carried along with both directions.

**5). Reinforcement**

In **one way slab** the slabs bends in one direction and to counter the bending of main steel that is crank bars are provided on shorter sides of the slabs or you can say that the main bars are provided in one direction only. The main diameter should be not less than 12 mm and the distribution bars should be not less than 8 mm.

**Two-way slabs,** the slabs bend in both direction hence main steel that is crank bars are provided on both sides of the slabs to counter this bending. or you can say that the main bars is provided in both directions. The main diameter should be not less than 12 mm and the distribution bars should be not less than 8 mm.

**6). Slab Thickness**

While designing a **one-way slab** we provide less steel hence the depth of slabs increases, as a result, the thickness of the one-way slab is more as compared to the two-way slab.The thickness of the one-way slab varies between 100 mm to 150 mm based on the deflection consideration and span.

Whereas, While designing the **two-way slab** we provide ore steel hence the depth of the slab decreases, as a result, the thickness of the two-way slab is less compared to the one-way slab.The usual thickness of two-way slabs is in the range of 100 mm to 200 mm depending upon span and deflection consideration.

**7).Types of Slabs**

There are mainly three types of design for one-way slab

a). One way solid slabs with beams.

b). One way ribbed slab with beams.

c). One way ribbed slab with integral beams.

**On the other hand**

There are mainly three types of design for two way slab

a). Two way solid slabs with beams.

b). Two-way waffle slab with beams.

c). One way Waffle slab with integral beams.

**8). Use**

For rectangular types of the plot having a width less than 12 feet or up to a span of 3.6 meters One-way slab can be economical.

Whereas, For Square types of the plot having width more than 12 feet or for the panel size up to 6 m x 6 m. A two-way slab can be less economical as compared to a one-way slab. In Practices, the choice of one way slab for a particular structure largely depends upon the

Economy.

Build-ability.

Loading Condition.

So, these are the differences between **One-way slab and Two-way slab**. I hope this article will be very useful for you all.

Thanks for your great attention to reading this post carefully.

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Good-Bye

Happy Learning 😆