What is the Main Bar and Distribution Bar

These two terms are generally used as the reinforcements of a slab.

Slab supported on two sides and bending takes place predominantly in one direction only is called One Way Slab. On the other hand, when slab is supported on all four sides and bending take place in two directions are said to be Two Way Slab.

The slabs having ratio of longer length to its shorter length (Ly/Lx) greater than 2 is called one way slab otherwise as two way slab. In one way slab main reinforcement is parallel to shorter direction and the reinforcement parallel to longer direction is called distribution steel.

In two way slab main reinforcement is provided along both direction.

Main Reinforcement Bars

Main reinforcement bar is provided at the shorter span direction in order to transfer the bending moment developed at the bottom of the slab. The purpose of providing main bar is to transfer the bending load developed at the bottom of the slab to the beams.

• Main reinforcement bar is provided at the bottom of the slab at the shorter direction.
• Stronger dimension bar is used as main bar.

In one way slab, the slab is supported by beams on the two opposite sides where main reinforcement bar is provided.

In two way slab, the slab is supported by beams on all four sides. So there will be no difference in bar size because each side will have to transfer equal amount of stress evenly.

Distribution Reinforcement Bars

• Distribution bars are provided to resist the shear stress, cracks developed in the longer span.
• Distribution bars are provided perpendicularly with the top of the main bar.
• Lesser dimension bars are used.
• Distribution bars are provided in the longer span direction.