In any reinforcement detailing there are two sizes of bars used in the slab. That is main reinforcement bars and distribution bars. In this article, we will discuss the difference between main bar and distribution bar.
To understand properly we need to know the bending moment on slab.
Let’s take an example.
When load is applied to a slab the bottom of the slab will experience positive moment (Sagging) and the supports will experience negative moments (Hogging). The bottom part, as well as the top part of the slab, will experience high tension at the same time.
The deflection will be very high in shorter span and low in longer span. High amount of tension will be acting in the support which is near than the other one.
Function Of 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.
1. Main reinforcement bar is provided at the bottom of the slab at the shorter direction.
2. 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.
Function Of Distribution 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.
Difference Between Main Bars And Distribution Bars:
- Main reinforcement bar is normally used at the bottom of the slab.
Distribution bars are placed on the top of the main bar.
- Main bar is used in shorter direction but distribution bar is used in longer span.
- Higher dimension bar is used as main reinforcement bar.
Lower dimension bar is used as distribution bars.
- Main reinforcement bar is used to transfer the bending moment to beams.
Distribution bars are used to resist the shear stress, and cracks developed at the top of the slab.