12 Difference Between One-Way And Two-Way Slab (With Comparison Chart)

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The slab is typically the horizontal structural element of any building/house which is used to construct floors, ceilings and roofs. Generally, slabs are made of reinforced concrete. They can be simply supported, continuous or cantilever.  Usually, the thickness of slabs is considerably less than their other dimensions. Slab can also be described as an element of the building which transfers the different types of floor load to the beams.

Slabs may have different shapes and support conditions. Depending upon their load carrying behavior, they are classified as one-way or two-way slabs. Other classifications include:

  • Precast
  • Pre-stressed
  • Cast in situ
  • Flat plates
  • Flat slabs
  • Waffle slabs
  • Ribbed (joist) slabs

What Is One Way Slab?

One way slab is a slab which is supported by parallel walls or beams on the two opposite sides to carry the load along one direction. A one-way slab because of its geometry, it is design for the spanning direction alone as it bends in only one direction. A span is the shorter side of slab in which load is transferred.

The main tension reinforcing bars therefore run parallel (spaced uniformly) to the shorter span and are usually placed at the bottom of slab. The thickness of one-way slab varies between 100mm to 150mm or even more depending upon the span and based on the deflection considerations. The one-way slabs are economical up to the span of 3.6m.

There are three main types of designs for one way slab. They include:

  • One-way Solid Slab with beams
  • One-way Ribbed Slab with beams
  • One-way Ribbed Slab with integral beams

What You Need To Know About One Way Slab

  1.  One way slabs are supported by the beams on the two opposite sides.
  2. Main reinforcement is provided on shorter span due to bending.
  3. Loads are carried along one direction in one way slab.
  4. Main reinforcement is provided in only one direction for one way slabs.
  5. One way slab is supported by parallel walls or beams whose length to breadth ratio is equal to or greater than two (L/B≥2).
  6. Deflected shape of one way slab is cylindrical in shape.
  7. One way slab bends or deflects in a direction perpendicular to the supporting edges while transferring the loads to the opposite supporting walls or beams.
  8. The thickness of one-way slab varies between 100 mm to 150mm based on the deflection consideration and span.
  9. The one way slab is economical up to a span of 3.6 meters.
  10. In one way slab, quantity of steel is less when compared to quantity of steel in two way slab.
  11. While designing one way slabs, less steel is employed hence the depth of the slab increases.
  12. Examples of one way slabs are Chajja and Varandha slabs.

What Is Two-Way Slab?

The two-way slab is a slab which 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 direction while transferring the loads to the walls or beams.

The two-way slab will deflect in a dish or saucer-like form under the action of loads. Corners of the two-way slab lift up if the slab is not cast monolithically with the supports (walls/beams). In two-way slabs, the main bars are provided in both directions and they are perpendicular to each other.

Usually, the thickness of two-way slabs varies between 100mm to 200mm depending upon span. The two-way slab is suitable and economical for the panel sizes up to 6m x 6m.

There are three main types of designs for two way slab. That is:

  • Two-way Solid slab with beams
  • Two-way Waffle Slab with beams
  • Two-way Waffle Slab with integral beams

What You Need To Know About Two Way Slab

  1. Two way slabs are supported by beams on all the four sides.
  2. Main reinforcement is provided in both sides due to bending that occurs on both sides.
  3. Loads are carried along both the directions in two way slabs.
  4. Main reinforcement is provided along both the directions in two way slabs.
  5. Two way slab is generally supported on all sides of the walls or beams or even 3 sides on beam, whose length to breadth ration is less than two (L/B<2).
  6. The deflected shape of two way slabs is dish or a saucer-like shape.
  7. Two way slab bend or deflect in both directions while transferring the loads to the walls or beams.
  8. The thickness of two way slabs is in the range of 100mm to 200mm depending upon span and deflection consideration.
  9. Two-way slab is economical for the panel sizes up to 6m x 6m.
  10. In two way slab, quantity of steel is more when compared to one way slab.
  11. While designing two way slabs, more steel is used hence the depth of the slab decreases.
  12. Example of two way slabs is Slabs used in the floor construction of multi-storey buildings.

Also Read: Difference Between Beam And Column

Difference Between One-Way And Two-Way Slab In Tabular Form

BASIS OF COMPARISON ONE-WAY SLAB TWO-WAY SLAB
Description One way slabs are supported by the beams on the two opposite sides.   Two way slabs are supported by beams on all the four sides.  
Main Reinforcement Main reinforcement is provided on shorter span due to bending.   Main reinforcement is provided in both sides due to bending that occurs on both sides.  
Loads Loads are carried along one direction in one way slab.   Loads are carried along both the directions in two way slabs.  
Reinforcement Main reinforcement is provided in only one direction for one way slabs.   Main reinforcement is provided along both the directions in two way slabs.  
Support One way slab is supported by parallel walls or beams whose length to breadth ratio is equal to or greater than two (L/B≥2).   Two way slab is generally supported on all sides of the walls or beams or even 3 sides on beam, whose length to breadth ration is less than two (L/B<2).  
Deflected Shape Deflected shape of one way slab is cylindrical in shape.   The deflected shape of two way slabs is dish or a saucer-like shape.  
Bending One way slab bends or deflects in a direction perpendicular to the supporting edges while transferring the loads to the opposite supporting walls or beams.   Two way slab bend or deflect in both directions while transferring the loads to the walls or beams.  
Thickness The thickness of one-way slab varies between 100 mm to 150mm based on the deflection consideration and span.   The thickness of two way slabs is in the range of 100mm to 200mm depending upon span and deflection consideration.  
Span The one way slab is economical up to a span of 3.6 meters.   Two-way slab is economical for the panel sizes up to 6m x 6m.  
Quantity Of Steel In one way slab, quantity of steel is less when compared to quantity of steel in two way slab.   In two way slab, quantity of steel is more when compared to one way slab.  
Designing While designing one way slabs, less steel is employed hence the depth of the slab increases.   While designing two way slabs, more steel is used hence the depth of the slab decreases.  
Examples Examples of one way slabs are Chajja and Varandha slabs.   Example of two way slabs is Slabs used in the floor construction of multi-storey buildings.  

Also Read: Difference Between I-Beam And H-Beam

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