Difference Between One Way Slab and Two Way Slab | What Is Slab? | What Is One-Way Slab? | What Is  Two Way Slab? | What Is Flat Slab? | What Is Grid Slab?

Difference Between One Way Slab and Two Way Slab

Table of Contents

What Is Slab?

In the structural system of buildings, slabs are an important element of the floor system. Slabs usually transfer loads such as gravity loads, dead loads, and live loads to a vertical framing system such as columns. Slabs are used as floor and ceiling in various buildings.

Slabs cover a large area of concrete in a building. So during an earthquake, various external forces are attracted to the surface of the slab.

Slabs are represented by different designs in different types of compositions. Such as to obtain flat surfaces in a particular building and as a deck slab of a bridge. The slab is usually formed by the structure of a reinforced concrete beam.

The two main types of slabs used in the construction of a building are widely used as one-way slabs and two-way slabs. This article provides information about the difference between a one-way slab and a two-way slab.

Also Read: Difference Between Dead Load Vs Live Load | Environmental Load

Function of Slab

Depending on the Design as Per the Requirement of the Structure, Some of the Main Functions of the Slab Are Shown Below:

  1. The slab provides a platform to work on the structure.
  2. The one-way slab or two-way slab method is properly used to transfer the load on the slab.
  3. The slab provides a flat surface to work with easily.
  4. The design of the multi-story building has been made possible by slabs.
  5. The slab can be used as a sound, heat as well as a fire insulator.
  6. The slab helps to keep the room private.

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

1. One-Way Slab

One-Way Slab

A one-way slab is designed in such a way that the load on the beam carries in one direction. The one-way slab is usually used for a short span.

According to IS 456: 2000, the ratio of long span (L) to short span (B) in one way slab is greater than 2.

Mathematically;

Longer Span / Shorter Span ≥ 2.

One-way slabs can be constructed only on two parallel beams or walls in building construction. One-way slabs are commonly used for short spans in a building.

The main reinforcement arranges reinforcement for one-way slabs in a short span and distribution reinforcement in a long span.

Also Read: What Is a Beam Bridge | Types of Beam Bridges | How Does a Beam Bridge Works | Advantage of Beam Bridge

Some examples of one-way slabs include cantilever slabs, chajja, and verandas.

  1. The supported slab on each of the two walls is always supported by one slab.
  2. A slab supported by less than four sides in a slab Structure in a building can be designed as a one-way slab.
  3. All cantilever slabs are simple examples of a one-way slabs.

2. Two Way Slab

Two Way Slab

Two-way slabs are supported from all four sides. The load is transferred in both directions through this slab. The main reinforcement for the structure of a two-way slab is given in both directions.

A two-way slab is designed when the ratio of a long span to a short span is less than two. This type of slab carries the load in two directions.

The thickness of the two-away slab depends on the deflection control criteria. In this type of slab, the reinforcement in the directions is designed to resist the bending moments.

Two-way slabs are commonly used to suit the needs of multi-story and commercial buildings.

3. Flat Slab

Flat Slab

A flat slab is a type of reinforced concrete slab. There are no beams and girders as support for the formation of a flat slab. In this type of flat slab, the load is transferred directly to the concrete columns.

Flat slabs are used by engineers for the construction of the building as required in different situations.

Some of the Advantages of the Flat Slab Are as Follows:

  1. The flat slab can be properly planned for partition walls.
  2. Using a flat slab for a building can give the owner the opportunity to choose a room layout as needed.
  3. Using a flat slab in a building eliminates the need for false ceilings.
  4. The floor height can be increased as no beams are used in the flat slab.

4. Grid Slab

Grid Slab

For a large room slab, a slab is formed over a number of beams on the column at the corner end. This type of slab structure is called a grid slab.

Sometimes grid slabs are designed for large column-free areas in large halls, public places, auditoriums, marriage halls, etc. For the formation of this type of slab, deep depth may be allowed for the column-to-column main beam.

Also Read: What Is Plum Concrete? | Plum Concrete Meaning | Plum Concrete Ratio

Analysis of Slab

The structural design of the slab is the same as that of the beam. The slab is analyzed as follows,

1. Elastic Analysis

The 1 m wide strips of the slab is analyzed as a base. The load on this base is calculated. Thus, a 1 m strip of the slab is analyzed by assuming a dummy beam as 1 m.

2. Code Coefficients:

The slab is analyzed by yield line theory. The analysis of the slab can be directly relied on as a coefficient, as shown in the code.

The calculation of redistribution of moments is not taken into account for slab analysis.

3. Yield Line Theory

Yield line theory is a method of analysis based on the final bending moment for the edge of a fall for a slab.

At collapse loads, the slab starts to crack because the slab is usually under-reinforced.

Reinforcement Details In Slab

The design of reinforcement in the slab is used to safely distribute the forces coming on the slab to the column.

1. One Way Slab Reinforcement Details

  • In a one-way slab, the load is transferred from one side to the other. In this type of slab, the maximum load will be transmitted over a long span. Therefore it is necessary to give proper reinforcement on the long-span side.
  • So in a one-way slab to provide adequate support to the long-span side, the main reinforcement is placed parallel to the short span by proper spacing, and the distribution reinforcement is placed on the long side according to the correct spacing.
  • Therefore, one-way slabs are preferred over the short span of the slab. Where main reinforcement is given on long-span due to bending. Reinforcement of one Way Slab is given as shown in the figure.

2. Two Way Slab Reinforcement Details

  • In a two-way slab, the applied external load is transferred to both sides in a long span and short span.
  • In two way slab, the main reinforcement is laid on both sides. In this type of slab, the load on both sides is evenly distributed.
  • In RCC two Way slab, each of the four sides is held on the beam by main reinforcement. A load of a two-way slab is transferred through structural elements such as beams.

Types of Loads Acting on Slab

There Are Different Loads on the Slab. This Is Shown as Follows:

  • Wind load
  • Live load
  • The dead load of the slab
  • Earthquake loads
  • Snow load

Difference Between One Way Slab and Two Way Slab

1. One Way Slab Vs Two Way Slab: Definition

  • In a one-way slab, the length of the long span is greater than the ratio of the short span to two.
  • In a two-way slab, the length of the long span is less than or equal to the ratio of the short span.

2. One Way Slab Vs Two Way Slab: Support

  • One-way slab Only two opposite sides are supported by a beam or wall.
  • The two-way slab is supported from all four sides.

3. One Way Slab Vs Two Way Slab: Transfer load

  • One Way Slab, the utmost load is transmitted by long span.
  • In Two Way, Slab load is transferred in both spans (long span and short span).

4. One Way Slab Vs Two Way Slab: Require Reinforcement

  • A one-way slab requires less reinforcement than a two-way slab.
  • Two-way slabs require more reinforcement than one-way slabs.

5. One Way Slab Vs Two Way Slab: Bending Moment

  • In one way slab, a bending moment occurs in a short span in only one direction one-way slab, a bending moment occurs in a short span in only one direction.
  • The bending moment in a two-way slab occurs in both directions, a longer span and a shorter span.

6. One Way Slab Vs Two Way Slab: Shape

  • The shape of a one-way slab is usually rectangular.
  • The shape of a two-way slab is usually square.

7. One Way Slab Vs Two Way Slab: Direction of Load Transfer

  • In one way slab, the load is transferred in one direction.
  • In a two-way slab, the load is transferred in both directions.

8. One Way Slab Vs Two Way Slab: Cost

  • One-way slabs are economically less expensive than two-way slabs.
  • Two-way slabs are economically more expensive than one-way slabs.

9. One Way Slab Vs Two Way Slab: Deflection

  • Deflection in a one-way slab gives it a cylindrical shape.
  • Deflection in a two-way slab makes it look like a bowl.

10. One Way Slab Vs Two Way Slab: Thickness

  • One-way slab thickness can be designed from 4 inches to 6 inches (100 mm to 150 mm) depending on deflection and span.
  • The thickness of the two-way slab can be designed from 4 inches to 8 inches (100 mm to 200 mm) depending on the deflection and span.

11. One Way Slab Vs Two Way Slab: Reinforcement Placing

  • In one way slab, main reinforcement is placed in a short span, and distributions reinforcement is placed in a long span.
  • In two way slab, the main reinforcement is placed in a short span and a long span.

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Frequently Asked Questions

Difference Between One Way Slab and Two Way Slab

In a one-way slab, the main source of load transmission is the longer direction. On the other hand, in the two-way slab, the shorter and larger sides are the main source for the transmission of load. In a one-way slab, the bending moment occurs in a singular direction, while in a two-way slab, it occurs in both directions.

What Is Slab?

A slab is a flat, two-dimensional planar structural component of the building having a very small thickness compared to its other two dimensions. Reinforced concrete slabs are used in roofs, floors, ceilings, and as the decks of bridges.

What Is 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.

What Is Two Way Slab?

The Building Structural Standard defines a two-way slab system as a concrete slab system in which two rebars are arranged in two directions regardless of the presence or absence of a beam that transmits a load to a column.

What Is Flat Slab?

A flat slab is a two-way reinforced concrete slab that usually does not have beams and girders, and the loads are transferred directly to the supporting concrete columns. The flat plate is a two-way reinforced concrete framing system utilizing a slab of uniform thickness, the simplest of structural shapes.

What Is Grid Slab?

Grid slab consists of ribs spaced at regular intervals in perpendicular directions, which are monolithic with the slab. These grid slabs are generally used for architectural purposes for large spans, such as public assembly halls, showrooms, and auditoriums, to avoid internal columns in the structure.

How to Design Two Way Slab?

  1. Step 1: Check the Type of Slab.
  2. Step 2: Preliminary dimensioning.
  3. Step 3: Load calculation.
  4. Step 4: Moment Calculation.
  5. Step 5: Check for Depth.
  6. Step 6: Reinforcement Calculation.
  7. Step 7: Check for shear stress.
  8. Step 8: Check for deflection.

How to Design Flat Slab?

2 Equivalent frame method Slab system is assumed as a rigid continuous frame. The direction of the offset notwithstanding the provision in (b), d) The successive span lengths in each direction shall not differ by more than one-third of the longer span.

Type of Slabs

  1. One-Way Flat Slab.
  2. Two-Way Flat Slab.
  3. Kitchen Slab.
  4. Sun Shade Slab.
  5. Lintel.
  6. Sunken Slab.
  7. Cable Suspension Slab.
  8. Pre-Tension Slab.

Flat Slab Construction

The flat slab construction is a reinforced concrete slab supported by the concrete columns directly without the support of the beams. So, we can say that a flat slab is a one-sided or two-sided system with a sheer load targeting the square slab or supporting columns.

Types of Flat Slab

Types of Flat Slab Construction

  1. Simple flat slab.
  2. Flat slab with drop panels.
  3. Flat slab with column heads.
  4. Flat slab with both drop panels and column heads.

Different Types of Slabs

The major types of concrete slabs used in construction are one-way joist slabs, flat slabs, flat plates, waffle slabs, hollow core slabs, precast slabs, slabs on grade, hardy slabs, and composite slabs.

Types of Slabs in Construction

What Are the 16 Different Types of Slabs in Construction?

  1. One-Way Flat Slab.
  2. Two-Way Flat Slab.
  3. Kitchen Slab.
  4. Sun Shade Slab.
  5. Lintel.
  6. Sunken Slab.
  7. Cable Suspension Slab.
  8. Pre-Tension Slab.

One Way Slab

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.

Two Way Slab

Two Way Slab
The two-way slab is a slab that is generally supported on all sides of walls or beams and whose length-to-breadth ratio is less than two, and it twists or bends in both directions while transferring the loads to the walls or beams.

Two Way Slab Reinforcement

Two Way Slab Reinforcement
In two way slab, main reinforcement is provided along both directions. Slabs could be simply supported, continuous, or cantilevered. In two way slab, the corners may be held down by restraints or may be allowed to lift up.

Function of Slab

Functions of Slab:
To provide a flat surface. To act as sound, heat, and fire insulators. It provides a covering shelter or working flat surface in buildings. Its primary function is to transfer the load by bending in one or two directions.

How to Make a Concrete Slab?

A concrete mix of 1 part cement: 2 parts sand: and four parts coarse aggregate should be used for a concrete slab. Concrete must be placed within half an hour of mixing. Place your concrete into your formwork; work the concrete into awkward places and corners using a shovel or trowel.

How to Make Expansion Joints in Concrete Slabs?

Space joints (in feet) are no more than 2-3 times the slab thickness (in inches). A 4″ slab should have joints 8-12 feet apart. When arranging joints, skilled contractors will often use them to create an attractive diamond pattern.

How to Do a Concrete Slab?

  1. Determining the Proper Depth. First and foremost, you have to identify and prepare the site where you plan to put down the slab.
  2. Dampening the Earth. Next, you need to dampen the soil.
  3. Laying Down the Base.
  4. Compacting Each Layer of the Base.
  5. Building Up the Concrete Formwork.

How to Make a Small Concrete Slab?

Standard concrete floor slab thickness in residential construction is 4 inches. Five to six inches is recommended if the concrete will receive occasional heavy loads, such as motor homes or garbage trucks.

How to Square a Concrete Slab?

To get a perfectly square corner, you want to aim for a measurement ratio of 3:4:5. In other words; you want a three-foot length on your straight line, a four-foot length on your perpendicular line, and a five-foot length across. If all three measurements are correct, you’ll have a perfectly square corner.

Reinforcement Details in Slab

Reinforcement detailing of a slab is done based on its support conditions. Slabs may be supported on walls or beams, or columns. Slabs supported directly by columns is called a flat slab. A slab supported on two sides and bending that takes place predominantly in one direction only is called One Way Slab.

What Is Waffle Slab?

A waffle slab or two-way joist slab is a concrete slab made of reinforced concrete with concrete ribs running in two directions on its underside. The name waffle comes from the grid pattern created by the reinforcing ribs.

What Is Ribbed Slab?

Ribbed slabs could also be called joist slabs or beam and joist slabs. These slabs have narrow concrete beams (joists) that span between larger, traditional concrete beams in the column lines. The joists are often 2′ to 3′ in the center.

What Is a Waffle Pod Slab?

Waffle slabs are reinforced concrete footing and slab systems constructed on the ground. They consist of a perimeter footing (edge beam) and a series of narrow internal beams (strip footings) at 1.2-meter nominal centers running each way through the slab.

What Is a Waffle Slab Foundation?

The Wafflemat foundation system, also called a waffle slab foundation, is an above-ground mat foundation used to provide load-bearing capacity on expansive, rocky, compressible, or hydro-collapsible soils.

Waffle Slab

Waffle pod slabs are effective for public buildings that carry a lot of weight due to their efficiency in vibration control. They have a two-directional reinforcement. This offers better vibration control capacity. It means the structure can stand the vibration created by crowd movements.

Ribbed Slab

Ribbed slabs are made up of wide band beams running between columns with narrow ribs spanning the orthogonal direction. Normally the ribs and the beams are the same depth. A thin topping slab completes the system. Waffle slabs tend to be deeper than the equivalent ribbed slab.

Waffle Pod Slab

The waffle pod system allows more accurate specification of concrete quantities, reduces waste, and boosts building site efficiency. Compared to another method of forming a slab, waffle pods create a more consistent, predictable foundation for your home.

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