What is difference between main bar and distribution bar

What is difference between main bar and distribution bar,What is main bar and distribution bar, when we need to design reinforcement details of slab we have 2 size of reinforcement Steel used in design of slab that is main bar and distribution bar for every civil engineer know about it. In this topic we know about what is difference between main bar and distribution bar.

"What

what is main rebar ?

the reinforcement having stronger dimension provided at the the bottom of slab in shorter direction to maintain the compressive stress developed by positive bending moment that is sagging and negative bending moment that is Hogging by transferring it into beam.

what is sagging

sagging describes the shape of beam when load is applied on it by middle of slab in downward direction and sagging describes a beam which curves downward due to positive bending moment.

Positive bending moment sagging

Positive bending moment sagging

what is hogging 

hogging describes the shape of beam when load is applied on it by middle of slab and it describes a beam which curves upward due to negative bending moment.

Negative bending moment that is hogging

Negative bending moment that is hogging

Let us discuss load applied on slab and their bending moment

Load is applied on middle of slab it transfer to to simply supported beam. When load is applied to slab then bottom of slab with experience positive bending moment in downward direction that is sagging and simply supported beam will experience negative bending moment that is hogging in upward direction. so the bottom and top part of slab experience very high Tension at the same time.

So the deflection will be very high in shorter span of main bar and low deflection in in longer span of distribution bar.

so main function of main bar is to transfer compressive stress or bending load developed at the bottom of slab developed by sagging and hogging to the beam. That’s why is stronger dimension of Steel required in main bar.

Bending moment when load is applied on slab

Bending moment when load is applied on slab

what is distribution bar?

the reinforcement having lesser dimension provided at the the top of slab in longer direction to resist the shear stress and cracks develop in longer span.

characteristics of distribution bar

1) distribution bar is provided perpendicular to main bar on top of slab in longer direction to resist the shear stress and cracks developed in longer Spain

2) lesser dimension of steel is used for the distribution bar in reinforcement design of slab

3) distribution bar is used in longer direction that’s why it is also known as longer span bar

4) it is perpendicular to the main bar that’s why it is also known as cross bar

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5) ultimate load carrying capacity of column

characteristics of main bar

1) main bar is provided at the bottom of slab

2) main bar is provided in shorter direction of slab

3) higher dimension of Steel used for main bar in reinforcement design of slab

4) main bar transfer bending moment load to the beam

"What

What is difference between main bar and distribution bar

1) main bar is provided at the bottom of slab but distribution bar is provided at the top of slab

2) main bar is used in shorter direction of slab that’s why it is called as shortest bar but distribution bar is used in longer direction of slab that’s why it is also known as longer span bar

3) high dimension of Steel used for main bar in reinforcement design of slab but lesser dimension of Steel used for distribution bar in reinforcement design of slab

4) the main purpose of providing main bar is to transfer the bending load developed due to sagging and hogging at the bottom of slab to the beam but main purpose of providing distribution bar is to rasist the shear stress and Crack develop in longer span.

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