# Necessity of Doubly Reinforced Section | Why do we provide doubly reinforced beam

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Table of Contents

## Why Do We Provide Doubly Reinforced Beam?

In This today The Civil Experiences article We Briefly explain What has doubly reinforced beam is, Why we provide doubly reinforced beam is provided (adopted) and the Necessity of the Doubly Reinforced Section

### Beam

The beam can be defined as a structural element that transfers structural load and resists bending. Its mode of deflection is primarily by bending.

### Concrete Beam

If Concrete plays a role in making a beam then it’s called a Concrete beam

### Reinforced Concrete beam

If Concrete and reinforcement play a role in making a beam then it’s called a Reinforced Concrete beam or RCC beam

## Types of Reinforced Beam

By Using of reinforcement position Reinforced Beam are further divided into two types of beam

Also Read: Types of Beam Mechanics

1. Singly Reinforced Beam
2. Doubly Reinforced Beam

### What is Doubly Reinforced Beam?

When steel reinforcements are provided in both of beam section tension zone and also in compression zone that type of beam is called a doubly reinforced beam / RCC beam

### What is the necessity of doubly R.C. Beam?

When the applied moment on the beam is more than the moment of resistance (M.R.) of the beam then the structural designer has the following kind of option
• To increase the depth of the beam
• To use a higher grade of concrete, to improve M.R.
• To provide reinforcements in the compression zone of the beam, to increase M.R.

Also Read: What is Hidden Beam and why used?

### Doubly R.C. Beam DEFINITION

When the applied moment on the beam element is more than the M.R. (moment of resistance) Of singly R.C. Beam the M.R. Of beam is increased by providing reinforcements in the compression zone. This type of beam is called doubly R.C. Beam

## Necessity of Doubly Reinforced Section

Doubly R.C. Beam is necessary for the following situation:-
1. when it is not possible or dimensions (breadth x depth) of the beam are restricted to increase the depth of beam due to architectural purpose
2. To get more headway in the rooms
3. When the beam is subjected to reversal of stresses
4. When subjected to an external load may cause tension on both faces of the member
5. When subjected to sudden load like in case of earthquakes
6. For pre-cast beams
7. When subjected to eccentric loading

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## Difference between singly and doubly reinforced beam

### Singly R.C. beam

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### Doubly R.C. beam

Ast = Area of steel in tension zone
Asc = Area of steel in compression zone

In the tension zone, Ast is provided

In the tension zone, Ast is provided

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In the compression zone, Acs is provided

In the compression zone, 2 – 10 Φ anchor bars are provided. The anchor bars are not designed to carry any compressive force

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In the compression zone, Asc is provided to resist compressive force

When Mu < Mu lim, the beam is designed as a singly R.C. beam

When Mu > Mu lim, the beam is designed as a doubly R.C. beam

Its M.R. is less

Its M.R. is more

Ductility is less

Ductility is more due to Asc in the compression zone

Not suitable where there are chances of a reversal of stresses

Suitable where there are chances of a reversal of stress ( for example During earth quack )

For the what is a beam, reinforced beam, Doubly beam and Necessity of Doubly Reinforced Section
Please read another post also you should read those important articles.

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