In which condition doubly reinforced beam is used?

Doubly reinforced beam is generally adopted in following conditions: When the size of the beam is confined. When the section of the beam is subjected to inversion stress. When the beam is nonstop more than a few backings.

Why are over reinforced beams not allowed by the code?

If over-reinforced beam is designed and loaded to full capacity then the steel in tension zone will not yield much before the concrete reaches its ultimate strain of 0.0035. This type of design is not recommended in practice of beam design.

What is the assumption in the steel beam theory of doubly reinforced beams?

In this theory, we assume concrete is weak in compression also then we get same amount of steel in both tension & compression, hence all the moment will be resisted by steel only and concrete will be of no use.

Why we use doubly reinforced beam?

Doubly reinforced beam is provided to increase the moment of resistance of a beam having limited dimensions. Minimum compression reinforcement is provided to hold the Shear Reinforcement (stirrups) in position and for increasing the ductility of beam.

Why is not preferred to design over reinforced section?

Why over-reinforced sections shall be avoided while designing the sections using limit state method? A section having percentage of tension steel greater than the critical percentage is known as over-reinforced section. Hence, this type of failure is usually avoided in ultimate strength design.

Why is doubly reinforced beam necessary?

Why doubly reinforced beam is preferred over singly reinforced beam?

If a beam with limited depth is reinforced only on the tension side, it may not be strong enough to withstand the bending moment. In order to increase the load capacity of the section moment. A doubly reinforced beam is provided to increase the strength of a beam with limited dimensions.