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.
A singly beam has reinforcement added to only one side of the concrete. This reinforcement is typically added to the bottom of the beam, where the tension forces are the greatest. The reinforcement is added to counteract the tensile stresses in the concrete that are generated when the beam is loaded.
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.
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.
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
Calculate the value of N by the given formula:
N= (mc)/(t+mc)
Where N = Critical Neutral AxixConstant.
Using this below method for Find the value of J.
J. =1- (N/3)
Where J is known as Lever arm constant
For Determine the moment of resistance coefficient
R=(1/2)JNc
Select appropriate breadth (b) and compare the bending moment and moment of resistance with the sufficient depth of that section.
d= sq root ([BM]/[Rb])
Calculate the value of At by the given formula
At = (BM)/(t.J.d)
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 a 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 reinforcements 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 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.
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.
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]
Or
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.
Mu – Mu 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
FAQs on Singly and Doubly Reinforced Beams
What Is a Singly Reinforced Beam?
A singly reinforced beam is a type of beam where reinforcement is provided only in the tension zone. The compressive forces are handled by the concrete section of the beam.
What Is a Doubly Reinforced Beam?
A doubly reinforced beam has reinforcement in both the tension and compression zones. This type of beam is used when architectural or structural constraints limit the depth of the beam.
When Should I Use a Singly Reinforced Beam?
Singly reinforced beams are typically used when the primary concern is to counteract tensile stresses due to bending. They are most effective when the beam’s depth is sufficient to handle the expected loads without additional reinforcement in the compression zone.
When Should I Use a Doubly Reinforced Beam?
Doubly reinforced beams are necessary when the depth of the beam is restricted and cannot be increased, and when higher moment of resistance is required. They are also used in situations where the beam is subject to alternating tension and compression or eccentric loading.
What Are the Main Differences Between Singly and Doubly Reinforced Beams?
The main difference lies in the placement of reinforcement. Singly reinforced beams have reinforcement only in the tension zone, while doubly reinforced beams have reinforcement in both tension and compression zones. This difference affects the beam’s ability to handle bending moments and shear stresses.
How Do I Calculate the Moment of Resistance for a Singly Reinforced Beam?
The moment of resistance for a singly reinforced beam can be calculated using the formula:
Moment of Resistance(MR)=0.87×fy×As×d(1−ad)\text{Moment of Resistance} (M_R) = 0.87 \times f_y \times A_s \times d \left(1 – \frac{a}{d}\right)
where fyf_y is the yield strength of steel, AsA_s is the area of tensile steel, dd is the effective depth, and aa is the depth of the neutral axis.
How Do I Calculate the Moment of Resistance for a Doubly Reinforced Beam?
For a doubly reinforced beam, the moment of resistance is the sum of the moments of resistance of the compression and tension zones. It can be calculated using:
Mu=Mu(lim)+Mu(extra)M_u = M_u(\text{lim}) + M_u(\text{extra})
where Mu(lim)M_u(\text{lim}) is the limiting moment of resistance for the singly reinforced section and Mu(extra)M_u(\text{extra}) is the additional moment due to the compression reinforcement.
What Are the Advantages of Using a Doubly Reinforced Beam?
Doubly reinforced beams allow for greater moment resistance without increasing the depth of the beam, making them suitable for scenarios with architectural or headroom constraints. They also provide additional strength to handle alternating or eccentric loads.
Why Is It Necessary to Place Two Reinforcement Bars in the Compression Zone of a Singly Reinforced Beam?
While singly reinforced beams primarily require reinforcement in the tension zone, two reinforcement bars are placed in the compression zone to hold the stirrups in position. These bars do not carry significant loads but ensure proper placement and stability of the stirrups.
Can Singly Reinforced Beams Handle Torsional Loads?
Singly reinforced beams are not typically designed to handle significant torsional loads. If torsion is a concern, additional longitudinal and shear reinforcement is necessary, often leading to the use of doubly reinforced beams.
What Are the Typical Applications of Singly Reinforced Beams?
Singly reinforced beams are commonly used in residential buildings, light commercial structures, and other scenarios where the primary load is vertical and the beam’s depth is sufficient to handle the loads without additional reinforcement.
What Are the Typical Applications of Doubly Reinforced Beams?
Doubly reinforced beams are used in structures with headroom constraints, such as basements or floors with limited ceiling height, and in scenarios where the beam is subject to high bending moments, eccentric loads, or alternating tension and compression forces.
