Why must compression reinforcement in a doubly reinforced beam be enclosed by stirrups?

Question

Question

This question was previously asked in

RRB JE CE 22 Apr 2025 Shift 1 CBT 2 Official Paper

Answer 1

Explanation:

In a doubly reinforced beam, the compression reinforcement is subjected to compressive forces.
Stirrups (transverse reinforcement) hold the compression bars in place, prevent lateral buckling, and contribute to concrete confinement, enhancing ductility and structural integrity.

Additional Information Doubly reinforced beams

Doubly reinforced beams are used when the depth of the beam is restricted or when higher moment resistance is needed than what a singly reinforced beam can provide.
In such beams, compression reinforcement is added in addition to tension reinforcement.
To ensure the stability of the compression bars, especially under heavy loads, they must be enclosed by stirrups.
Stirrups serve multiple purposes: they resist shear, hold longitudinal bars in place, and prevent buckling of compression steel.
Confinement of concrete by stirrups also improves the ductility and energy absorption capacity of the beam, which is especially important in seismic zones.