What Is Singly Beam & Doubly Beam

What Is Singly Beam?

A singly beam is the beam which is provided with longitudinal reinforcement in the tension zone. Compressive forces are handled by the concrete section in the beam.

What Is Doubly Beam?

The beams reinforced with steel in compression and tension zones are known as doubly reinforced beams. This kind of beam will be found essential when headroom consideration or architectural concern the depth of the beam is restricted.

The beam with its restricted depth, if reinforced provided on the tension side only, it may not have sufficient moment of resistance to resist the bending moment.

By raising the quantity of steel in the tension zone, the moment of resistance cannot be increased indefinitely. Generally, the moment of resistance can be increased by not more than 25% beyond the balance moment of resistance by making the beam reinforced on the tension face.

Hence, to additional increase, the moment of resistance of a beam section of unlimited dimensions, a doubly reinforced beam is provided.

Also, read: What is Plum Concrete | Application | Mix Design | Methodology

Based on Implanted Reinforcement

Singly Reinforced Beam

Reinforcements are provided to oppose tensile stresses due to shear and bending in beams for singly reinforced beam sections. Practically, for singly reinforced beams, two additional bars are supplied in the compression face of the beam so that stirrups can be tied with bars easily. These extra reinforcements are of the nominal diameter of 8mm or 10mm.

Doubly Reinforced Beam

When the depth of the section is restricted due to reasons like, such as architectural reasons or basement floors, the beam section is designed as a doubly reinforced concrete beam.

These bars shall withstand in compressive stresses and are provided with reinforcement in compression face.
Beams, when subjected to in torsion, are provided additional longitudinal and shear reinforcement to resist bending, and shear stresses developed due to torsion.

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Singly Reinforced Beam:

The beam, which is longitudinally reinforced only in the tension zone, is known as a singly reinforced beam. In Such beams, the decisive bending moment and tension due to that bending are carried by the reinforcement, while the concrete concedes the compression.

We take it Practically; it is not possible to make available reinforcement only in the tension zone, due to we need to tie the stirrups with it. Therefore, at that place, two rebars are utilized in the compression zone to fasten the stirrups, and the rebars work as false members just for the stirrups holder.34

The loads Handel by a beam are transferred to walls, columns, or girders, which then transfer the force to adjoining structural compression members.

Procedure of Singly Reinforced Beam Design

1.Calculate the value of N by the given formula:

[Where N = Critical Neutral AxixConstant.]

2. using this below method for Find the value of J.

Where J is known as Lever arm constant

3. for Determine the moment of resistance coefficient

4. Select appropriate breadth (b) and compare the bending moment and moment of resistance with the sufficient depth of that section.

5. Calculate the value of At by the given formula

Where At = Area of tensile steel.

T = Allowable tensile stress in steel.

For a particular Beam section, It is necessary to give Reinforcement(Steel Bars) in the Compression and Tension zone. If the reinforcement is only in tension zone, then it is called Singly Reinforcement Beam, and on another hand, if the reinforcement is in both the Tension and Compression zone, then it is called Doubly reinforced Beam.

In both cases, there will be load in tension and compression zone. This is because; it is not possible to figure a Beam structure without stirrups.

To hold the stirrups in its standing position, it is necessary to place two reinforcement in the compression zone of singly reinforced Beam. However, those two will never carry or pass loads in its body, and it is just fake.

In a Beam, the topmost section is called the Compression zone, and the bottom part is called the Tension zone.

Rcc Beams Info:

RCC beams are built-in cement concrete reinforced with using the reinforced bars. Where Beams resist tensile and compression adds stiffness to the structure.

Beams generally manage vertical gravitational forces, but it can also be used to handle horizontal loads (i.e., loads placed due to wind and an earthquake ). The loads carry by the beam are moveable to walls, columns, or girders, which then transfer the force to adjoining structural compression members. In light-frame construction, the joists rest on the beam.

Also, read: What Is Cover in Concrete | Clear Cover in Beams, Slab, Column, Footing

Doubly Reinforced Beam:

This article intends to discuss types of beam construction and RCC design of supported reinforced beam.
This doubly beam is also used in the following given situations;

⦁ The outsider live loads may alternate, I .e.it may occur on both faces of the member.
For example:

⦁ A pile maybe pull up in that manner, the tension and compression zones may alternate in all case.

⦁ The loading types may be eccentric, and the eccentricity of the load may be changeable from one side of the axis to the other side of the axis.

⦁ The member may be intended to a shock or impact or accidental lateral thrust.

Also, read: Concrete Mix Ratio | What Is Concrete Mix Ratio | Type of Concrete Mix Ratio

Procedure for the Doubly Reinforced Beam Is Given Below;

Step 1

calculate the moment of resistance(limiting) for the given cross-section (Mu lim) using the formula for singly reinforced beam

Mu lim = 0.87.fy.Ast1.d [1 – 0.42Xumax]
for Balanced section in a beam

Ast1 = (0.36Xumax.fck.b)/(0.87fy)

step 2

factored moment Mu > Mu lim, then a doubly reinforced beam is necessary to be designed for an extra moment.
MuMu lim = fsc.Asc (d – d’) [fsc value from code page no. 70]

Step 3

Additional area of tension steel Ast2

Ast2 =Asc.fsc/0.87fy

Step 4

Total tension steel Ast, Ast = Ast1 + Ast2

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Krunal Rajput: Hey, I am Krunal Rajput. The Man Behind CivilJungle. I started this site to spread knowledge about Civil/Mechanical/Electrical Engineering. I am a Degree Holder in Civil Engineering.