In this article today we will discuss about what is main bar and distribution bars in the slab. and also different b/w main bars and distribution bars, but for main bars and distribution bars there is two things one is Bending moment and Shear Stress. So after reading this article you will be able that what is main bar and distribution bars in slab and also their different with bending moment and shear stress.

## Function of Main Bars

Main bars are placed at the shorter span direction to transfer the bending moment (B.M) developed at the bottom of the slab to the beam.

also read: What is Admixture in Concrete

1: Main bars (M.B) are placed at the shorter span direction in the slab.

2: Main bars (M.B) are used at the bottom of the slab.

3: For Main bars (M.B) we select the high dimension of steel in the slab.

4: in one way slab the slab is supported at one direction or one side, so therefore we should be placed the main bar at the shorter span.

read more : Download Full House Drawing in AutoCAD

## Function of Distribution Bars

Distribution bars (D.B) are used in the slab to resist the shear stress. Because the cracks are developed to share stress on the top of the . and it should be placed at the longer span of the slab.

1: Distribution bars (D.B) are placed at the longer span direction in the slab.

2: Distribution bars (D.B) are used at the Top of the slab.

3: Distribution bars (D.B) we have to select the lesser dimensions of steel, because it just use to resist the shear stress in the slab.

### What is Bending Moment?

Bending moment is the force which can normally measure in a force X length (kNm.) it doesn’t have unit. So bending moment is basically force that causes something to bend in the structure. And bending moment can calculate from different section of the beam or slab. ** OR **Bending moment is the rotational force which acts on the beam. Girder , slab or column sections. It usually refer normal force which is Sigma =My/I . Where M= Moments , Y = Distance form one point to the center of the member and I = Moment of Inertia.

### What is Shear Stress?

also read: How to Select Size of Septic Tank?

Simply we can define that shear stress is the external force which acting on an object or any surface parallel to the slop plane. And shear stress is the force tending to bring the deformation in the materials by slippage along plane of the object parallel to the imposed stress. And the resulted shear force is the movement of the materials and to earthquakes. And bending moment and shear force both can be occur in one time in the beam or slab etc.

written by: Engr Sami Ullah Stanikzai

Fore more detail watch the given video:

Read more: Download Advanced Steel Structures Notes for free

also read: Standards Dimension for Stairs

## Comments

## Dennis

What if the slab is square…all the spans are equal…how can u determine which one is main and which is distribution bar…?

## zacharia

thank u for being creat this page