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

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.