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What is the Difference between main bars and distribution bars in slab

What is the Difference between main bars and distribution bars in slab

Let us go through some of the FAQs to understand the main bars & distribution bars in a slab.

1. What are the main bars in a slab .?

The reinforcement bars that are placed in the tension zone of the slab to resist the bending moment & to transfer the superimposed loads to the supports that are provided for the slab are called main bars.

Main bars are always placed at the bottom part of the slab reinforcement and distribution bars rest over the main bar as shown in the above drawing.

The diameter of the main bar should not be less than 8mm for the HYSD bar and 10mm for plain bars.

2. What are the distribution bars in a slab .?

The reinforcement bars that are placed above the main bar in a one-way slab, to distribute the superimposed load to the main bar are called distribution bars.

As you can observe in the above drawing, distribution bars are provided in the longer span of the one-way slab & main bars are placed along the shorter span of the slab.

The distribution bar helps to firmly hold the main bars in their assigned position. They also act against shrinkage stresses due to temperature variations.

3. Is distribution bars provided in a two-way slab .?

The term distribution bar is sometimes used for the top reinforcement of all types of slabs. But in actuality, it is not correct in the case of a two-way slab as the load is transferred in both directions. So in the two-way slabs, the reinforcement provided in both the Lx & Ly directions should be called main bars.

4. What are the different functions of main bars in concrete .?

1. To transfer the superimposed loads to the supports.

2. To resist the bending moments.

3. To withstand shear stress in the tension zone.

4. To encounter shrinkage cracks due to temperature variation.

5. What are the different functions of distribution bars in concrete .?

1. To distribute the superimposed load to the main bar.

2. To firmly hold the main bars in their given position.

3. To form a mesh with the main bar in concrete for better bonding strength.

4. To resist shrinkage stress due to climatic variation.

5. To resist the development of cracks due to external factors.

2. How to calculate the cutting length of reinforcement bars in circular R.C.C slab

6. What are the differences between main bars & distribution bars in a slab?

 No. Main bar Distribution bar 1. Used in shorter direction. Used in longer direction of one-way slab.
 2 Placed in bottom part of slab reinforcement. Placed over the top of the main bar.

 3 Higher diameterÂ Â  bars are used. Lower diameter bars are used.

 4 Designed to resist bendingÂ  Â  Â  moment. Not designed to resist bending moment.

 5 Transfers super imposed load toÂ Â  the supports Distributes super imposed load to the main bar.

 6 Resists shear stress at the tension zone. Resists shrinkage stress due to climatic variation.