# Difference Between One Way Slab And Two Way Slab | What is Slab

In this civil experience article, we explain the difference between **one way slab** and **two way slab** (One way slabs vs Two way slabs) in detail also provide one way slab and two way slab design excel sheet so read and share with friends and join us for more important learning

Before going on a particular type of slab take an eye on what is slab so you can better understand

## What is Slab?

A **slab** is a structural member to provide **flat horizontal surfaces** in luxury building floors, roofs, bridges, and other types of structures.

Difference Between One Way Slab And Two Way Slab |

The slab rest on walls, by reinforced concrete beams normally **cast monolithically** with the slab, by structural steel beams, either by columns or from the ground.

A slab thickness and it is supported by other structural elements like RCC columns, RCC beams, walls, or the ground surface.

The cement concrete slab with top and bottom surfaces are parallel. The depth of a **concrete slab** is very small compared to its span or length.

In the building component, there are two major **types of slabs** used in building construction one-way slabs and two-way slabs. In this article, we will discuss **what is the Difference Between One Way Slab and Two Way Slab**

**Type of Slabs Based on Support Conditions**

- One Way Slab
- Two Way Slab
- Flat Slab Resting Direction on a Column Without Beam
- Grid Slabs or Waffle Slab
- Circular Slab and Other Shapes

## What is a One Way Slab?

According to **Indian Standard Code** IS 456:2000, The ratio of longer span (l) to shorter span (b) which is known as (L/B) ratio greater than 2 is known as One way slab.

In practice, **One way slab** is supported by only two parallel beams or walls. Normally we don’t use one-way slabs often.

One Way Slab |

A one way slab is defined as a flexural member with thickness small relative to other slab dimensions, gravity loads applied normal to and directly above **slab surface**, a span in one direction between parallel supports and fortified for flexure in this direction only.

If the slab is supported on **two opposite sides**, it is called a **one way spanning slab**. In this **type of slab**, loads are transferred on two opposite as per the above figure A

If the slab is supported at **four sides**, and if Ly/Lx ≥ 2 one way spanning slab.

When any slab has Ly = Lx condition, the slab has a tendency to bend in both directions. With an increase of Ly, the tendency of bending along Ly is reduced and that on Lx is increased.

When Ly/Lx ≥ 2, the slab bends only in X directions

When Ly/Lx ≥ 2, the slab is called a one way slab. (One way slab formula)

In one way slab, the main reinforcement is provided along with Lx ( Short Span)

### One Way Slab Definition

When Ly/Lx ≥ 2, the slab is called a one way slab.

The **one-way slab** is a slab, which is supported by parallel walls or beams, and whose **length to breadth ratio is equal to or greater than two** and it bends in only one direction (spanning direction) while it is transferring the loads to the two supporting walls or beams, because of its geometry. Simply stating it spans and bends in only one direction.

### One Way Slab Reinforcement Details

Commonly a One-Way Slab, as one side is greater than the other one, the utmost load will be transmitted by the larger side. Accordingly, it is necessary to contribute sufficient support to the larger side.

To provide sufficient support to the extended side, the main reinforcement bars are placed parallel to the shorter side and the distribution bars are placed on the longer side which does not support transmitting the load.

So, a one-way slab is chosen where main bars or cranked bars are provided on the shorter side of the slab due to bending. Distribution bars (straight bars) provided on the longest side as shown in the figure.

### One Way Slab Design

One way slab design example calculation manually is long but shorter than two way slab design so according to expert engineers use of software like Microsoft excel for one way slab reinforcement detail design with all cross check for safety such as Download from below

## What is a Two Way Slab?

A **two way slab** is a street which allows the load to travel in both directions.

The design considerations of wall supported **two way slabs** are similar to one way slabs.

Two Way Slab |

The thickness of the slab is generally based on deflection control criteria, and the reinforcements in the two orthogonal directions are designed to resist the calculated maximum bending moments in the respective directions at the critical sections.

Additional reinforcement may be required at the corners of two way slabs in some cases, as explained later.

The **slab thickness** should be sufficient against shear, although shear is usually not a **problem in two way slabs** subjected to uniformly distributed loads.

If the slab is supported at all four edges and if Ly/Lx < 2, (two way slab formula)

The tendency of the slab is to bend in both directions. Such slab is called **two way slab** as per above figure c

In two way slabs, main reinforcement is provided along with Lx as well as Ly direction

### Two Way Slab Reinforcement Details

In the 2 way slab, as the loads are acting in both the direction i.e. longer and shorter direction.

In this type of slab, the main reinforcement bars are laid in both directions. The loads held up by two sides in this type of slabs are equal.

You can recognize the main bars are placed on both sides. The **RCC slab** is held up by beams on every four sides and the loads are upheld by **structural components** such as beams along with both directions.

Slab with reinforcement steel in both directions is more practicable and supportive than one-way reinforcement slabs.

Download Excel spreadsheet for design Two Way Slab Reinforcement Details easily with high accuracy in less time

### Types of Two-Way Slab

I'm sure that not every civil engineer is not aware of all slab design types of two-way slab but in the construction xls sheet we cover each and every major and minor type of two-way slab to serve the best experience

- Interior panel
- One short edge discontinuous
- One long edge discontinuous
- Two adjacent edges discontinuous
- Two short edges discontinuous
- Two long edges discontinuous
- Three edges discontinuous(one long edge continuous)
- Three edges discontinuous(one Short edge continuous)
- Four edges discontinuous

## What is Grid Slab?

When the slab is supported on beams with column only on the periphery of the hall, the slab is called grid slab. Sometimes, in large halls, public places, marriage halls, auditoriums, etc. a large column free area is required.

In these cases, large deep beams may be permitted, but the columns are permitted only on the periphery.

## Difference Between One Way Slab And Two Way Slab

One Way Slab | Two Way Slab |

The one way slab is supported by a beam on two opposite side only. |
The two way slab is supported by the beam on all four sides. |

The utmost load is carried by the larger side. |
The loadings are imposed and held up in both directions i.e. longer and shorter directions. |

Ly/Lx ≥ 2 one way slab spanning. | Ly/Lx < 2 two way slab spanning |

One way slab design using Excel Sheet Download one way slab excel |
Two way slab design using Excel Sheet Download Two way slab excel |

In one way slab, the load is carried in one direction perpendicular to the supporting beam. | In two way slab, the load is carried in both directions. |

If L/b the ratio is greater than or equal to 2 or then it is considered a one-way slab. |
If L/b the ratio is less than 2 then it is considered a two-way slab. |

One way slab two opposite side support beam /wall | Two Way Slab four side mins all side supported beam /wall |

One way slab is bending only in one spanning side direction while load transfer | In two-way slab, the crank is provided in four directions. |

One way slab is bent only in one spanning side direction while load transfer | Two way slab is bent both spanning side directions while load transfer |

In one-way slab, the load is carried in one direction perpendicular to the supporting beam. | In two-way slab, the load is carried in both directions. |

Chajja and Varandha are practical examples of the one way slab. | Whereas two-way slabs are used in constructive floors of the Multistorey building. |

The deflected shape of the one-way slab is cylindrical. |
Whereas the deflected shape of the two-way slab is a dish or saucer-like shape. |

In one-way slab quantity of steel is less. | In two-way slab quantity of steel is more as compared to the one-way slab. |

Main Reinforcement is in provide short span due to banding. |
Main Reinforcement is in provide short span due to banding |

One way slab near about 100mm to 150mm based on the deflection. | Two way slabs are in the range of 100mm to 200mm depending upon |

One way slab economical near about 3.5 m. | Two way slab may be economical for the panel sizes near about 6m x 6m. |

## Mechanism of Load Transfer In Slab

The forces transfer from slab to beam occur in one way or two ways. The whole system completely depends on the geometrical dimensions of the slab.

If slabs may be supported by columns only, in this case, two-way action will prevail.

If the ratio of long side / short side > 2 it is considered as one-way slab, and if longer side to shorter side ratio < 2 then it is considered as a two-way slab.

The load transfer mechanism from concrete slab floor to supporting elements for one-way slab and two-way slab is shown in the figure.

## Reinforcement Details In Slab

Reinforcement arrangement in a slab is the main parameter to understand the system of forces and safely distribute the loads coming on the slab.

## FAQ1: What is Slab?

In civil engineering concrete slab is a common structural member of modern buildings construction, consisting of a flat, horizontal surface made of cast concrete. Steel reinforced slabs, typically between 100 and 500 mm thick, are most often used to construct floors and ceilings, while thinner mud slabs may be used for exterior paving.

## FAQ2: One Way Slab and Two Way Slab

The one–way slab is supported by a beam on two opposite sides only. On the hand The two–way slab is supported by the beam on all four sides. In one–way slab, the load is carried in one direction perpendicular to the supporting beam but In two–way slab, the load is carried in both directions.

## FAQ3: One Way Slab

One way slab is a slab that is supported by beams on the two opposite sides to carry the load in one direction only. The ratio of longer span (l) to shorter span (b) is equal or greater than 2, considered as One-way slab because this slab will bend in one direction i.e in the direction along its shorter span

## FAQ4: One Way Slab Design

One way slab design example calculation manually is long but shorter than two-way slab design so according to expert engineers use of software like Microsoft excel for one way slab reinforcement detail design with all cross-check for safety such as Download from Civil Experience

## FAQ5: One Way Slab Reinforcement Details

Commonly a One-Way Slab, as one side is greater than the other one, the utmost load will be transmitted by the larger side. Accordingly, it is necessary to contribute sufficient support to the larger side. To provide sufficient support to the extended side, the main reinforcement bars are placed parallel to the shorter side and the distribution bars are placed on the longer side which does not support transmitting the load. So, a one-way slab is chosen where main bars or cranked bars are provided on the shorter side of the slab due to bending. Distribution bars (straight bars) provided on the longest side as shown in the figure.

## FAQ6: One Way Vs Two Way Slab

In one–way slab, the load is transferred in one direction perpendicular to the supporting beam. In two–way slab, the load is transferred in both directions. The deflected shape of the one–way slab is cylindrical. Whereas the deflected shape of the two–way slab is a dish or saucer-like shape.

## FAQ7: What is a Two Way Slab?

Two–way means moving or working in two opposite directions or allowing something to move or work in two opposite directions. The bridge is now open to two–way traffic.

## FAQ8: What is Difference Between One Way Slab and Two Way Slab?/summary>
In one way slab, the load is transferred in one direction perpendicular to the supporting beam. In two–way slab, the load is transferred in both directions.
The deflected shape of the one–way slab is cylindrical and on another side, the deflected shape of the two–way slab is a dish or saucer-like shape.

In one way slab, the load is transferred in one direction perpendicular to the supporting beam. In two–way slab, the load is transferred in both directions. The deflected shape of the one–way slab is cylindrical and on another side, the deflected shape of the two–way slab is a dish or saucer-like shape.

## FAQ9: How many Types of Two-Way Slab?

1. Interior panel 2. One short edge discontinuous 3. One long edge discontinuous 4. Two adjacent edges discontinuous 5. Two short edges discontinuous 6. Two long edges discontinuous 7. Three edges discontinuous(one long edge continuous) 8. Three edges discontinuous(one Short edge continuous) 9. Four edges discontinuous